instrument_scripts/nksp/01_nksp.html

<html>
  <head>
    <meta name="author" content="Christian Schoenebeck">
    <title>NKSP Language</title>
    <meta name="description" content="Introduction to the NKSP real-time instrument script language.">
  </head>
  <body>
    <p>
      This document intends to give you a compact introduction and overview to
      the NKSP real-time instrument script language, so you can start writing
      your own instrument scripts in short time. It concentrates on describing
      the script language. If you rather want to learn how to modify and
      attach scripts to your sounds, then please refer to the gigedit manual for
      <a href="gigedit_scripts.html">how to manage instrument scripts with gigedit</a>
      for Gigasampler/GigaStudio format sounds, or refer to the SFZ opcode
      <code lang="sfz">script</code> for attaching NKSP scripts with
      SFZ format sounds.
    </p>

    <h3>At a Glance</h3>
    <p>
      <img src="nksp_file.png" style="height:111px; margin-right:12px;">
      NKSP stands for "is <b>N</b>ot <b>KSP</b>", which denotes its distinction
      to an existing proprietary language called <i>KSP</i>.
      NSKP is a script language specifically designed to write real-time capable
      software extensions to LinuxSampler's sampler engines that can be bundled
      individually with sounds by sound designers themselves.

      Instead of defining a completely new script language, NKSP is leaned on
      that mentioned properiatary script language. The biggest advantage is that
      sound designers and musicians can leverage the huge amount of existing KSP
      scripts which are already available for various purposes on the Internet,
      instead of being forced to write all scripts from scratch in a completely
      different language.
    </p>
    <p>
      That also means however that there are some differences between those two
      languages. Some extensions have been added to the NKSP core language to
      make it a bit more convenient and less error prone to write scripts, and
      various new functions had to be added due to the large difference of the
      sampler engines and their underlying sampler format. Efforts have been
      made though to make NKSP as much compatible to KSP as possible.
      The NKSP documentation will emphasize individual differences in
      the two languages and function implementations wherever they may occur, to
      give you immediate hints where you need to take care of regarding
      compatibility issues when writing scripts that should be spawned on both
      platforms.
    </p>
    <p>
      Please note that the current focus of NKSP is the sound controlling aspect
      of sounds. At this point there is no support for the graphical user
      interface function set of KSP in NKSP.
    </p>

    <h2>Event Handlers</h2>
    <p>
      NKSP is an event-driven language. That means you are writing so called
      <i>event handlers</i> which define what the sampler shall do on individual
      events that occur, while using the sound the script was bundled with.
      An event handler in general looks like this:
    </p>
    <code lang="nksp">
on ??event-name??

  ??statements??

end on
    </code>
    <p>
      There are currently six events available:
    </p>
      <table>
        <tr>
          <th>Event Type</th> <th>Description</th>
        </tr>
        <tr>
          <td><code>on note</code></td> <td>This event handler is executed when a new note was triggered, i.e. when hitting a key on a MIDI keyboard.</td>
        </tr>
        <tr>
          <td><code>on release</code></td> <td>This event handler is executed when a note was released, i.e. when releasing a key on a MIDI keyboard.</td>
        </tr>
        <tr>
          <td><code>on controller</code></td> <td>This event handler is executed when a MIDI control change event occurred. For instance when turning the modulation wheel at a MIDI keyboard.</td>
        </tr>
        <tr>
          <td><code>on rpn</code></td> <td>This event handler is executed when a MIDI <i>RPN</i> event occurred.</td>
        </tr>
        <tr>
          <td><code>on nrpn</code></td> <td>This event handler is executed when a MIDI <i>NRPN</i> event occurred.</td>
        </tr>
        <tr>
          <td><code>on init</code></td> <td>Executed only once, as very first event handler, right after the script had been loaded. This code block is usually used to initialize variables in your script with some initial, useful data.</td>
        </tr>
      </table>
    <p>
      You are free to decide for which ones of those event types you are going to
      write an event handler for. You can write an event handler for only one
      event type or write event handlers for all of those event types. Also
      dependent on the respective event type, there are certain things you can
      do and things which you can't do. But more on that later.
    </p>
    
    <h3>Note Events</h3>
    <p>
      As a first example, the following tiny script will print a message to your
      terminal whenever you trigger a new note with your MIDI keyboard.
    </p>
    <code>
on note
  message("A new note was triggered!")
end on
    </code>
    <p>
      Probably you are also interested to see which note you triggered exactly.
      The sampler provides you a so called
      <i title="A script variable which is provided by the sampler and which has a very specific purpose which you cannot override for other purposes.">
        built-in variable
      </i>
      called <code>$EVENT_NOTE</code> which reflects the note number
      (as value between 0 and 127) of the note that has just been triggered. Additionally
      the built-in variable <code>$EVENT_VELOCITY</code> provides you the
      velocity value (also between 0 and 127) of the note event.
    </p>
    <code>
on note
  message("Note " & $EVENT_NOTE & " was triggered with velocity " & $EVENT_VELOCITY)
end on
    </code>
    <p>
      The <code>&</code> character concatenates text strings with each other.
      In this case it is also automatically converting the note number into a
      text string.
    </p>
    <note class="important">
      The message() function is not appropriate for being used with your final
      production sounds, since it can lead to audio dropouts.
      You should only use the message() function to try out things, and to spot
      and debug problems with your scripts.
    </note>
    
    <h3>Release Events</h3>
    <p>
      As counter part to the <code>note</code> event handler, there is also the
      <code>release</code> event handler, which is executed when a note was
      released. This event handler can be used similarly:
    </p>
    <code>
on release
  message("Note " & $EVENT_NOTE & " was released with release velocity " & $EVENT_VELOCITY)
end on
    </code>
    <p>
      Please note that you can hardly find MIDI keyboards which support release
      velocity. So with most keyboards this value will be 127.
    </p>

    <h3>Controller Events</h3>
    <p>  
      Now let's extend the first script to not only show note-on and note-off
      events, but also to show a message whenever
      you use a MIDI controller (i.e. modulation wheel, sustain pedal, etc.).
    </p>
    <code>
on note
  message("Note " & $EVENT_NOTE & " was triggered with velocity " & $EVENT_VELOCITY)
end on

on release
  message("Note " & $EVENT_NOTE & " was released with release velocity " & $EVENT_VELOCITY)
end on

on controller
  message("MIDI Controller " & $CC_NUM " changed its value to " & %CC[$CC_NUM])
end on
    </code>
    <p>
      It looks very similar to the note event handlers. <code>$CC_NUM</code>
      reflects the MIDI controller number of the MIDI controller that had been
      changed and <code>%CC</code> is a so called <i>array variable</i>, which not only
      contains a single number value, but instead it contains several values at
      the same time. The built-in <code>%CC</code> array variable contains the current
      controller values of all 127 MIDI controllers. So <code>%CC[1]</code> for
      example would give you the current controller value of the modulation
      wheel, and therefore <code>%CC[$CC_NUM]</code> reflects the new controller
      value of the controller that just had been changed.
    </p>
    <p>
      There is some special aspect you need to be aware about: in contrast to the MIDI standard,
      monophonic aftertouch (a.k.a. channel pressure) and pitch bend wheel are
      handled by NKSP as if they were regular MIDI controllers. So a value change
      of one of those two triggers a regular <code>controller</code> event handler
      to be executed. To obtain the current aftertouch value you can use
      <code>%CC[$VCC_MONO_AT]</code>, and to get the current pitch bend wheel
      value use <code>%CC[$VCC_PITCH_BEND]</code>.
    </p>

    <h3>RPN / NRPN Events</h3>
    <p>
      There are also dedicated event handlers for
      MIDI <i title="Registered Parameter Number">RPN</i> and
      <i title="Non-Registered Parameter Number">NRPN</i>
      events:
    </p>
    <code>
on rpn
  message("RPN address msb=" & msb($RPN_ADDRESS) & ",lsb=" & lsb($RPN_ADDRESS) &
          "-> value msb=" & msb($RPN_VALUE) & ",lsb="  & lsb($RPN_VALUE))
  if ($RPN_ADDRESS = 2)
    message("Standard Coarse Tuning RPN received")
  end if
end on

on nrpn
  message("NRPN address msb=" & msb($RPN_ADDRESS) & ",lsb=" & lsb($RPN_ADDRESS) &
          "-> value msb=" & msb($RPN_VALUE) & ",lsb="  & lsb($RPN_VALUE))
end on
    </code>
    <p>
      Since MIDI RPN and NRPN events are actually MIDI controller events,
      you might as well handle these with the previous
      <code>controller</code> event handler. But since RPN and NRPN messages
      are not just one MIDI message, but rather always handled by a set of
      individual MIDI messages, and since the
      precise set and sequence of actual MIDI commands sent varies between
      vendors and even among individual of their products, it highly makes sense to
      use these two specialized event handlers for these instead, because the
      sampler will already relief you from that burden to deal with all those
      low-level MIDI event processing issues and all their wrinkles involved
      when handling RPNs and NRPNs.
    </p>
    <note>
      Even though there are two separate, dedicated event handlers for RPN and NRPN events,
      they both share the same built-in variable names as you can see in the
      example above.
    </note>
    <p>
      So by reading <code>$RPN_ADDRESS</code> you get the RPN / NRPN parameter
      number that had been changed, and <code>$RPN_VALUE</code> represents the
      new value of that RPN / NRPN parameter. Note that these two built-in
      variables are a 14-bit representation of the parameter number and new
      value. So their possible value range is <code>0 .. 16383</code>. If you
      rather want to use their (in MIDI world) more common separated two 7 bit
      values instead, then you can easily do that by wrapping them into either
      <code>msb()</code> or <code>lsb()</code> calls like also demonstrated above.
    </p>

    <h3>Script Load Event</h3>
    <p>
      As the last one of the six event types available with NKSP, the following
      is an example of an <code>init</code> event handler.
    </p>
    <code>
on init
  message("This script has been loaded and is ready now!")
end on
    </code>
    <p>
      You might think, that this is probably a very exotic event. Because in
      fact, this "event" is only executed once for your script: exactly when
      the script was loaded by the sampler. This is not an unimportant event
      handler though. Because it is used to prepare your script for various
      purposes. We will get more about that later.
    </p>

    <h2>Comments</h2>
    <p>
      Let's face it: software code is sometimes hard to read, especially when you
      are not a professional software developer who deals with such kinds of
      things every day. To make it more easy for you to understand, what you
      had in mind when you wrote a certain script three years ago, and also if
      some other developer might need to continue working on your scripts one
      day, you should place as many comments into your scripts as possible. A
      comment in NKSP is everything that is nested into an opening and closing
      pair of curly braces.
    </p>
    <code>{ This is a comment. }</code>
    <p>
      You cannot only use this to leave some human readable explanations here
      and there, you might also use such curly braces to quickly disable parts
      of your scripts for a moment, i.e. when debugging certain things.
    </p>
    <code>
on init
  { The following will be prompted to the terminal when the sampler loaded this script. }
  message("My script loaded.")

  { This code block is commented out, so these two messages will not be displayed }
  { 
    message("Another text")
    message("And another one")
  }
end on
    </code>
    
    <h2>Variables</h2>
    <p>
      In order to be able to write more complex and more useful scripts, you
      also need to remember some data somewhere for being able to use that
      data at a later point. This can be done by using
      <i title="A variable is a storage location paired with an associated symbolic name.">
        variables
      </i>.
      We already came across some <i>built-in variables</i>, which are already
      defined by the sampler for you. To store your own data you need to declare
      your own <i>user variables</i>, which has the following form:
    </p>
    <p>
      <code>declare $??variable-name?? := ??initial-value??
    </p>
    <p>
      The left hand side's <code>??variable-name??</code> is an arbitrary name
      you can chose for your variable. That name might consist of English
      letters A to Z (lower and upper case), digits (<code>0</code> to <code>9</code>),
      and the underscore character "<code>_</code>".
      Variable names must be unique. So you can neither declare several variables
      with the same name, nor can you use a name for your variable that is
      already been reserved by <i>built-in variables</i>.
      The right hand side's <code>??initial-value??</code> is simply the first
      value the variable should store right after it was created. You can also
      omit that.
    </p>
    <p>
      <code>declare $??variable-name??
    </p>
    <p>
      In that case the sampler will automatically assign <code>0</code> for you
      as the variable's initial value. This way we could for example count the
      total amount of notes triggered.
    </p>
    <code>
on init
  declare $numberOfNotes := 0
end on

on note
  $numberOfNotes := $numberOfNotes + 1

  message("This is the " & $numberOfNotes & "th note triggered so far.")
end on
    </code>
    <p>
      In the <code>init</code> event handler we create our own variable
      <code>$numberOfNotes</code> and assign <code>0</code> to it as its
      initial value. Like mentioned before, that initial assignment is optional.
      In the <code>note</code> event handler we then increase the
      <code>$numberOfNotes</code> variable by one, each time a new note was
      triggered and then print a message to the terminal with the current total
      amount of notes that have been triggered so far.
    </p>
    <note>
      NKSP allows you to declare variables in all event handlers, however if
      you want to keep compatibility with KSP, then you should only
      declare variables in <code>init</code> event handlers.
    </note>

    <h3>Variable Types</h3>
    <p>
      There are currently five different variable types, which you can easily
      recognize upon their first character.
    </p>
    <table>
      <tr>
        <th>Variable Form</th> <th>Data Type</th> <th>Description</th>
      </tr>
      <tr>
        <td><code>$??variable-name??</code></td> <td>Integer Scalar</td> <td>Stores one single integer number value.</td>
      </tr>
      <tr>
        <td><code>%??variable-name??</code></td> <td>Integer Array</td> <td>Stores a certain amount of integer number values.</td>
      </tr>
      <tr>
        <td><code>~??variable-name??</code></td> <td>Real Number Scalar</td> <td>Stores one single real (floating point) number value.</td>
      </tr>
      <tr>
        <td><code>???variable-name??</code></td> <td>Real Number Array</td> <td>Stores a certain amount of real (floating point) number values.</td>
      </tr>
      <tr>
        <td><code>@??variable-name??</code></td> <td>String</td> <td>Stores one text string.</td>
      </tr>
    </table>
    <p>
      So the first character just before the actual variable name, always
      denotes the data type of the variable. Also note that all variable types
      share the same variable name space. That means you cannot declare a
      variable with a name that has already been used to declare a variable of
      another variable type.
    </p>
    
    <h3>Array Variables</h3>
    <p>
      We already used the first two variable types. However we have not seen yet
      how to declare such array variables. This is the common declaration form
      for creating your own array variables.
    </p>
    <code>
on init
  declare %??variable-name??[??array-size??] :=  ( ??list-of-values?? )
end on
    </code>
    <p>
      So let's say you wanted to create an array variable with the first 12
      prime numbers, then it might look like this.
    </p>
    <code>
on init
  declare %primes[12] :=  ( 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 )
end on
    </code>
    <p>
      Like with integer variables, assigning some initial values with
      <code>??list-of-values??</code> is optional. The array
      declaration form without initial value assignment looks like this.
    </p>
    <code>
on init
  declare %??variable-name??[??array-size??]
end on
    </code>
    <p>
      When you omit that initial assignment, then all numbers of that array will
      automatically be initialized with <code>0</code> each. With array
      variables however, it is always mandatory to provide
      <code>??array-size??</code> with an array
      variable declaration, so the sampler can create that array with the
      requested amount of values when the script is loaded. In contrast to many
      other programming languages, changing that amount of values of an array
      variable is not possible after the variable had been declared. That's due
      to the fact that this language is dedicated to real-time applications, and
      changing the size of an array variable at runtime would harm real-time
      stability of the sampler and thus could lead to audio dropouts. So NKSP
      does not allow you to do that.
    </p>


    <h3>String Variables</h3>
    <p>
      You might also store text with variables. These are called <i>text string
      variables</i>, or short: <i>string variables</i>. Let's skip the common declaration
      form of string variables and let us modify a prior example to just use
      such kind of variable.
    </p>
    <code>
on init
  declare $numberOfNotes
  declare @firstText := "This is the "
  declare @secondText
end on

on note
  $numberOfNotes := $numberOfNotes + 1
  @secondText := "th note triggered so far."
  message(@firstText & $numberOfNotes & @secondText)
end on
    </code>
    <p>
      It behaves exactly like the prior example and shall just give you a
      first idea how to declare and use string variables.
    </p>
    <note class="important">
      Like with the message() function, you should not use string variables
      with your final production sounds, since it can lead to audio dropouts.
      You should only use string variables to try out things, and to spot
      and debug problems with your scripts.
    </note>

    <h3>Variable Scope</h3>
    <p>
      By default, all variables you declare with NKSP are
      <i title="A variable that is accessible throughout an entire script.">
        global variables
      </i>. That means every event handler can access the data of such a global
      variable. Furthermore, each instance of an event handler accesses the same
      data when it is referencing that variable. And the latter fact can be a
      problem sometimes, which we will outline next.
    </p>
    <p>
      Let's assume you wanted to write an instrument script that shall resemble
      a simple delay effect. You could do that by writing a note event handler
      that automatically triggers several new notes for each note being
      triggered on a MIDI keyboard. The following example demonstrates how that
      could be achieved.
    </p>
    <code>
on init
  { The amount of notes to play }
  declare const $delayNotes := 4
  { Tempo with which the new notes will follow the orignal note }
  declare const $bpm := 90
  { Convert BPM to microseconds (duration between the notes) }
  declare const $delayMicroSeconds := 60 * 1000000 / $bpm
  { Just a working variable for being used with the while loop below }
  declare $i
  { For each successive note we trigger, we will reduce the velocity a bit}
  declare $velocity
end on

on note
  { First initialize the variable $i with 4 each time we enter this event
    handler, because each time we executed this handler, the variable will be 0 }
  $i := $delayNotes

  { Loop which will be executed 4 times in a row }
  while ($i)
    { Calculate the velocity for the next note being triggered }
    $velocity := 127 * $i / ($delayNotes + 1)
    { Suspend this script for a short moment ... }
    wait($delayMicroSeconds)
    { ... and after that short break, trigger a new note. }
    play_note($EVENT_NOTE, $velocity)
    { Decrement loop counter $i by one }
    $i := $i - 1
  end while
end on
    </code>
    <p>
      In this example we used a new keyword <code>const</code>. This additional
      variable qualifier defines that we don't intend to change this variable
      after declaration. So if you know beforehand, that a certain variable should
      remain with a certain value, then you might use the <code>const</code>
      qualifier to avoid that you i.e. change the value accidently when you
      modify the script somewhere in future.
    </p>
    <p>
      Now when you trigger one single note on your keyboard with that script,
      you will hear the additional notes being triggered. And also when you
      hit another note after a while, everything seems to be fine. However if
      you start playing quick successive notes, you will notice something goes
      wrong. The amount of notes being triggered by the script is now incorrect
      and also the volume of the individual notes triggered by the script is wrong.
      What's going on?
    </p>
    <p>
      To understand the problem in the last example, let's consider what is
      happening when executing that script exactly: Each time you play a note
      on your keyboard, a new instance of the <code>note</code> event handler
      will be spawned and executed by the sampler. In all our examples so far
      our scripts were so simple, that in practice only one event handler instance
      was executed at a time. This is different in this case though. Because
      by calling the <code>wait()</code> function, the respective handler
      execution instance is paused for a while and in total each handler
      instance will be executed for more than 2 seconds in this particular
      example. As a consequence, when
      you play multiple, successive notes on your keyboard in short time, you
      will have several instances of the <code>note</code> event handler running
      simultaniously. And that's where the problem starts. Because by default,
      as said, all variables are global variables. So the event handler instances
      which are now running in parallel, are all reading and modifying the same
      data. Thus the individual event handler instances will modify the
      <code>$i</code> and <code>$velocity</code> variables of each other, causing
      an undesired misbehavior.
    </p>
    <note>
      NKSP's built-in function <code>play_note()</code> allows you to pass
      between one and four function arguments. For the function arguments you
      don't provide to a <code>play_note()</code> call, NKSP will automatically
      use default values. If you want your script to be compatible with KSP,
      then you should always pass four arguments to that function though.
    </note>

    <h3>Polyphonic Variables</h3>
    <p>
      As a logical consequence of the previously described data concurrency
      problem, it would be desirable to have each event handler instance use
      its own variable instance, so that the individual handler instances stop
      interfering with each other. For this purpose the so called
      <i title="A variable which is effectively a separate variable for each event handler instance.">
        polyphonic variable
      </i>
      qualifier exists with NKSP. Declaring such a variable is identical to
      declaring a regular variable, just that you add the keyword <code>polyphonic</code>.
    </p>
    <code>
declare polyphonic $??variable-name??
    </code>
    <p>
      So to fix the bug in our previous example, we simply make the variables
      <code>$i</code> and <code>$velocity</code> polyphonic variables.
    </p>
    <code>
on init
  { The amount of notes to play }
  declare const $delayNotes := 4
  { Tempo with which the new notes will follow the orignal note }
  declare const $bpm := 90
  { Convert BPM to microseconds (duration between the notes) }
  declare const $delayMicroSeconds := 60 * 1000000 / $bpm
  { Just a working variable for being used with the while loop below }
  declare polyphonic $i  { < --- NOW POLYPHONIC !!! }
  { For each successive note we trigger, we will reduce the velocity a bit}
  declare polyphonic $velocity  { < --- NOW POLYPHONIC !!! }
end on

on note
  { First initialize the variable $i with 4 each time we enter this event
    handler, because each time we executed this handler, the variable will be 0 }
  $i := $delayNotes

  { Loop which will be executed 4 times in a row }
  while ($i)
    { Calculate the velocity for the next note being triggered }
    $velocity := 127 * $i / ($delayNotes + 1)
    { Suspend this script for a short moment ... }
    wait($delayMicroSeconds)
    { ... and after that short break, trigger a new note. }
    play_note($EVENT_NOTE, $velocity)
    { Decrement loop counter $i by one }
    $i := $i - 1
  end while
end on
    </code>
    <p>
      And that's it! The script works now as intended. Now you might wonder, why
      are variables not <i>polyphonic</i> by default? Isn't that more common and
      wouldn't that be more safer than using global variables by default? The reason is that
      a polyphonic variable consumes a lot more memory than a regular (global) variable.
      That's because for each polyphonic variable, the sampler has to allocate
      in advance (when the script is loaded) as many instances of that
      polyphonic variable as there are maximum events
      allowed with the sampler. So that's a lot! Considering that today's
      computers have plenty of RAM this might be a theoretical aspect, but in the
      end: this default scope of variables was already like this with <i>KSP</i>
      so we are also doing it like this with NKSP for compatibility reasons.
    </p>
    <p>
      Please note that the <i>polyphonic</i> qualifier only exists for integer
      variables. So you cannot declare polyphonic string variables, nor can you
      declare polyphonic array variables. Like in the previous explanation,
      this is due to the fact that it would consume a huge amount of memory
      for such variables. And with string variables and array variables, the
      required amount of memory would be much higher than with simple integer
      variables.
    </p>
    <p>
      As summary, the following are guideline rules describing when you should
      use the polyphonic qualifier for a certain variable. You should declare
      a particular variable polyphonic if one (or even both) of the following two
      conditions apply to that variable.
    </p>
    <ol>
      <li>
        If you call the <code>wait()</code> function within your event
        handlers and the respective variable is modified and read before
        and after at least one of the individual <code>wait()</code> calls.
      </li>
      <li>
        If you have loops that might run for a very long time, while accessing
        the respective variable in between. That's because if your script is
        running consecutively for too long, the sampler will automatically suspend your
        script for a while to avoid your script becoming a real-time stability
        hazard for the sampler. Your script will then automatically be resumed
        after a short moment by the sampler, so effectively this is similar to
        something like an "automated" <code>wait()</code> function call by
        the sampler.
      </li>
    </ol>
    <p>
      In all other cases you should rather use regular (global) variables instead.
      But keep in mind that you might need to re-assign a certain value for
      some global variables when you enter the respective event handler, just
      like we did with <code>$i := $delayNotes</code> right from the start
      during discussion of the previous example script.
    </p>
    <p>
      There is another special aspect regarding the variable scope of polyphonic
      variables: <code>note</code> handlers and <code>release</code> handlers of
      the same script share the same polyphonic variable scope, that means you
      may pass data from a particular note's <code>note</code> handler to its
      <code>release</code> handler by using the same polyphonic variable name.
    </p>

    <h2>Control Structures</h2>
    <p>
      A computer is more than a calculator that adds numbers and stores them
      somewhere. One of the biggest strength of a computer, which makes it
      such powerful, is the ability to do different things depending on various
      conditions. For example your computer might clean up your hard drive
      while you are not sitting in front of it, and it might immediately stop
      doing so when you need all its resources to cut your latest video which
      you just shot.
    </p>
    <p>
      In order to do that for you, a computer program allows you to define
      conditions and a list of instructions the computer shall
      perform for you under those individual conditions. These kinds of
      software mechanisms are called <i>Control Structures</i>.
    </p>
    
    <h3>if Branches</h3>
    <p>
      The most fundamental control structure are <i>if branches</i>, which has
      the following general form.
    </p>
    <code>
if (??condition??)
  
  ??statements??

end if
    </code>
    <p>
      The specified <code>??condition??</code> is evaluated each time script
      execution reaches this control block. The condition can for example be
      the value of a variable, some arithmetic expression, a function call or
      a combination of them. In all cases the sampler expects the
      <code>??condition??</code> expression to evaluate to some numeric
      (or boolean) value. If the evaluated number is exactly <code>0</code> then
      the condition is interpreted to be <i>false</i> and thus the list of
      <code>??statements??</code> is not executed. If the evaluated value is any
      other value than <code>0</code> then the condition is interpreted to be
      <i>true</i> and accordingly the list of <code>??statements??</code> will be
      executed.
    </p>
    <p>
      Alternatively you might also specify a list of instructions which shall be
      executed when the condition is <i>false</i>.
    </p>
    <code>
if (??condition??)

  ??statements-when-true??

else

  ??statements-when-false??

end if
    </code>
    <p>
      In this case the first list of statements is executed when the
      <code>??condition??</code> evaluated to <i>true</i>, otherwise the second
      list of statements is executed instead.
    </p>
    <p>
      Once again, let's get back to the example of counting triggered notes.
      You might have noticed that it did not output correct English for the
      first three notes. Let's correct this now.
    </p>
        <code>
on init
  declare $numberOfNotes
  declare @postfix
end on

on note
  $numberOfNotes := $numberOfNotes + 1

  if ($numberOfNotes == 1)
    @postfix := "st"
  else
    if ($numberOfNotes == 2)
      @postfix := "nd"
    else
      if ($numberOfNotes == 3)
        @postfix := "rd"
      else
        @postfix := "th"
      end if
    end if
  end if

  message("This is the " & $numberOfNotes & @postfix & " note triggered so far.")
end on
    </code>
    <p>
      We are now checking the value of <code>$numberOfNotes</code> before we
      print out a message. If <code>$numberOfNotes</code> equals one, then we
      assign the string <code>"st"</code> to the variable <code>@postfix</code>,
      if <code>$numberOfNotes</code> equals 2 instead we assign the string
      <code>"nd"</code> instead, if it equals 3 instead we assign
      <code>"rd"</code>, in all other cases we assign the string
      <code>"th"</code>. And finally we assemble the text message to be
      printed out to the terminal on line 23.
    </p>

    <h3>Select Case Branches</h3>
    <p>
      The previous example now outputs the numbers in correct English. But the
      script code looks a bit bloated, right? That's why there is a short hand
      form.
    </p>
    <code>
select ??expression??

  case ??integer-1??
  
    ??statements-1??

    
  case ??integer-2??
  
    ??statements-2??
    
          .
          .
          .      
end select
    </code>
    <p>
      The provided <code>??expression??</code> is first evaluated to an integer
      value. Then this value is compared to the integer values of the nested
      <code>case</code> lines. So it first compares the evaluated value of
      <code>??expression??</code> with <code>??integer-1??</code>, then it
      compares it with <code>??integer-2??</code>, and so on. The first integer
      number that matches with the evaluated value of <code>??expression??</code>,
      will be interpreted as being the current valid condition. So if
      <code>??expression??</code> equals <code>??integer-1??</code>,
      then <code>??statements-1??</code> will be executed, otherwise if
      <code>??expression??</code> equals <code>??integer-2??</code>,
      then <code>??statements-2??</code> will be executed, and so on.
    </p>
    <p>  
      Using a select-case construct, our previous example would look like follows.
    </p>
    <code>
on init
  declare $numberOfNotes
  declare @postfix
end on

on note
  $numberOfNotes := $numberOfNotes + 1
  @postfix := "th"

  select $numberOfNotes
    case 1
      @postfix := "st"
    case 2
      @postfix := "nd"
    case 3
      @postfix := "rd"
  end select

  message("This is the " & $numberOfNotes & @postfix & " note triggered so far.")
end on
    </code>
    <note>
      If you like, you can also put parentheses around the select expression,
      like <code>select (??expression??)</code>. Some developers familiar with
      other programming languages might prefer this style. However if you want
      to keep compatibility with KSP, you should not use parentheses for
      select expressions.
    </note>
    <p>  
      The amount
      of case conditions you add to such select-case blocks is completely up
      to you. Just remember that the case conditions will be compared one by one,
      from top to down. The latter can be important when you define a case line
      that defines a value range. So for instance the following example will
      not do what was probably intended.
    </p>
    <code>
on init
  declare $numberOfNotes
end on

on note
  $numberOfNotes := $numberOfNotes + 1

  select $numberOfNotes
    case 1 to 99
      message("Less than 100 notes triggered so far")
      exit
    case 1
      message("First note was triggered!") { Will never be printed ! }
      exit
    case 2
      message("Second note was triggered!") { Will never be printed ! }
      exit
    case 3
      message("Third note was triggered!") { Will never be printed ! }
      exit
  end select

  message("Wow, already the " & $numberOfNotes & "th note triggered.")
end on
    </code>
    <p>
      You probably get the idea what this script "should" do. For the 1st note
      it should print <code>"First note was triggered!"</code>, for the 2nd
      note it should print <code>"Second note was triggered!"</code>, for the 3rd
      note it should print <code>"Third note was triggered!"</code>, for the 4th
      up to 99th note it should print <code>"Less than 100 notes triggered so far"</code>,
      and starting from the 100th note and all following ones, it should print
      the precise note number according to line 23. However, it doesn't!
    </p>
    <p>
      To correct this problem, you need to move the first case block to the end,
      like follows.
    </p>
    <code>
on init
  declare $numberOfNotes
end on

on note
  $numberOfNotes := $numberOfNotes + 1

  select $numberOfNotes
    case 1
      message("First note was triggered!")
      exit
    case 2
      message("Second note was triggered!")
      exit
    case 3
      message("Third note was triggered!")
      exit
    case 1 to 99
      message("Less than 100 notes triggered so far")
      exit
  end select

  message("Wow, already the " & $numberOfNotes & "th note triggered.")
end on
    </code>
    <p>
      Or you could of course fix the questioned case range from <code>case 1 to 99</code>
      to <code>case 4 to 99</code>. Both solutions will do.
    </p>
    <p>
      We also used the <i>built-in function</i> <code>exit()</code> in the
      previous example. You can use it to stop execution at that point of your
      script. In the previous example it prevents multiple messages to be
      printed to the terminal.
    </p>
    <note class="important">
      The <code>exit()</code> function only stops execution of the <b>current</b>
      event handler instance! It does <b>not</b> stop execution of other
      instances of the same event handler, nor does it stop execution of other
      handlers of other event types, and especially it does <b>not</b> stop or
      prevent further or future execution of your entire script! In other words,
      you should rather see this function as a return statement, in case you are
      familiar with other programming languages already.
    </note>
    
    <h3>while Loops</h3>
    <p>
      Another fundamental control construct of program flow are loops.
      You can use so called
      <i title="Repeats a given list of instructions until the defined condition turns false.">
        while loops
      </i>
      with NKSP.
    </p>
    <code>
while (??condition??)

  ??statements??

end while
    </code>
    <p>
      A while loop is entered if the provided <code>??condition??</code>
      expression evaluates to <i>true</i> and will then continue to execute
      the given list of <code>??statements??</code> down to the end of the statements
      list. The <code>??condition??</code> is re-evaluated each time execution
      reached the end of the <code>??statements??</code> list and according to
      that latest evaluated <code>??condition??</code> value at that point, it
      will or will not repeat executing the statements again. If the condition
      turned <i>false</i> instead, it will leave the loop and continue executing
      statements that follow after the while loop block.
    </p>
    <p>
      The next example will print the same message three times in a row to the
      terminal, right after the script had been loaded by the sampler.
    </p>
    <code>
on init
  declare $i := 3
  
  while ($i)
    message("Print this three times.")
    $i := $i - 1
  end while
end on
    </code>
    <p>
      When the while loop is reached for the first time in this example, the
      condition value is <code>3</code>. And as we learned before, all integer
      values that are not <code>0</code> are interpreted as being a <i>true</i> condition.
      Accordingly the while loop is entered, the message is printed to the
      terminal and the variable <code>$i</code> is reduced by one. We reached
      the end of the loop's statements list, so it is now re-evaluating the
      condition, which is now the value <code>2</code> and thus the loop
      instructions are executed again. That is repeated until the loop was
      executed for the third time. The variable <code>$i</code> is now
      <code>0</code>, so the loop condition turned finally to <i>false</i> and the
      loop is thus left at that point and the text message was printed
      three times in total.
    </p>

    <h3>User Functions</h3>
    <p>
      We already came across various built-in functions, which you may call
      by your scripts to perform certain tasks or behavior which is already
      provided for you by the sampler. NKSP also allows you to write your
      own functions, which you then may call from various places of your
      script.
    <p>  
    </p>
      When working on larger scripts, you
      may notice that you easily get to the point where you may have to
      duplicate portions of your script code, since there are certain things
      that you may have to do again and again in different parts of your script.
      Software developers usually try to avoid such code duplications to
      keep the overall amount of code as small as possible, since the 
      overall amount of code would bloat quickly and would
      make the software very hard to maintain. One way for you to avoid such
      script code duplications with NKSP is to write so called <i>User Functions</s>.
    </p>
    <p>
      Let's assume you wanted to create a simple stuttering effect. You may do so
      like in the following example.
    </p>
    <code>
on note
  while (1)
    wait(200000)
    if (not (event_status($EVENT_ID) .and. $EVENT_STATUS_NOTE_QUEUE))
      exit()
    end if
    change_vol($EVENT_ID, -20000)  { Reduce volume by 20 dB. }
    wait(200000)
    if (not (event_status($EVENT_ID) .and. $EVENT_STATUS_NOTE_QUEUE))
      exit()
    end if
    change_vol($EVENT_ID, 0)  { Increase volume to 0 dB. }
  end while
end on
    </code>
    <p>
      This script will run an endless loop for each note being triggered.
      Every <code lang="none">200ms</code> it will turn the volume alternatingly down and
      up to create the audible stuttering effect. After each <code lang="nksp">wait()</code>
      call it calls <code>event_status($EVENT_ID)</code> to check whether
      this note is still alive, and as soon as the note died, it will stop
      execution of the script instance by calling <code>exit()</code>. The latter
      is important in this example, because otherwise the script execution instances would
      continue to run in this endless loop forever, even after the respectives
      notes are gone. Which would let your CPU usage increase with every new note
      and would never decrease again.
      This behavior of the sampler is not a bug, it is intended, since there may
      also be cases where you want to do certain things by script even after the
      respective notes are dead and gone. However as you can see, that script is
      using the same portions of script code twice. To avoid that, you could also
      write the same script with a user function like this:
    </p>
    <code>
function pauseMyScript
  wait(200000)
  if (not (event_status($EVENT_ID) .and. $EVENT_STATUS_NOTE_QUEUE))
    exit()
  end if
end function
    
on note
  while (1)
    call pauseMyScript
    change_vol($EVENT_ID, -20000)  { Reduce volume by 20 dB. }
    call pauseMyScript
    change_vol($EVENT_ID, 0)  { Increase volume back to 0 dB. }
  end while
end on
    </code>
    <p>
      The script became in this simple example only slightly smaller, but it also
      became easier to read and behaves identically to the previous solution.
      And in practice, with a more complex script, you can
      reduce the overall amount of script code a lot this way. You can choose any
      name for your own user functions, as long as the name is not already
      reserved by a built-in function. Note that for calling a user function,
      you must always precede the actual user function name with the
      <code>call</code> keyword. Likewise you may however not use the
      <code>call</code> keyword for calling any built-in function. So that
      substantially differs calling built-in functions from calling user functions.
    </p>

    <h3>Synchronized Blocks</h3>
    <p>
      When we introduced the <a href="#polyphonic_variables">polyphonic keyword</a>
      previously, we learned that a script may automatically be suspended by
      the sampler at any time and then your script is thus sleeping for an
      arbitrary while. The sampler must do such auto suspensions under certain
      situations in cases where an instrument script may become a hazard for the
      sampler's overall real-time stability. If the sampler would not do so, then
      instrument scripts might easily cause audio dropouts, or at worst, buggy
      instrument scripts might even lock up the entire sampler in an endless
      loop. So auto suspension is an essential feature of the sampler's real-time
      instrument script engine.
    </p>
    <p>
      Now the problem as a script author is that you don't really know beforehand
      why and when your script might get auto suspended by the sampler. And when
      you are working on more complex, sophisticated scripts, you will notice
      that this might indeed be a big problem in certain sections of your scripts.
      Because in practice, a sophisticated script often has at least one certain
      consecutive portion of statements which must be executed in strict consecutive order
      by the sampler, which might otherwise cause concurrency issues and thus
      misbehavior of your script if that sensible code section was auto suspended
      in between. A typical example of such concurrency sensible code sections are
      statements which are reading and conditionally modifying global variables.
      If your script gets auto suspended in such a code section, another
      script handler instance might then interfere and change those global
      variables in between.
    </p>
    <p>
      To avoid that, you can place such a sensible code section at the very beginning
      of your event handler. For example consider you might be writing a custom
      <i title="A consecutive pitch glide from one note to another note.">glissando</i>
      script starting like this:
    </p>
    <code>
on init
  declare $keysDown
  declare $firstNoteID
  declare $firstNoteNr
  declare $firstVelocity
end on

on note
  { The concurrency sensible code section for the "first active" note. }
  inc($keysDown)
  if ($keysDown = 1 or event_status($firstNoteID) = $EVENT_STATUS_INACTIVE)
    $firstNoteID = $EVENT_ID
    $firstNoteNr = $EVENT_NOTE
    $firstVelocity = $EVENT_VELOCITY
    exit { return from event handler here }
  end if

  { The non-sensible code for all other subsequent notes would go here. }
end on

on release
  dec($keysDown)
end on
    </code>
    <p>
      Because the earlier statements are executed in an event handler, the higher
      the chance that they will never get auto suspended. And with those couple of
      lines in the latter example you might even be lucky that it won't ever get
      suspended in that sensible code section at least. However when it comes to live
      concerts you don't really want to depend on luck, and in practice such a
      sensible code section might be bigger than this one.
    </p>
    <p>
      That's why we introduced <code>synchronized</code> code blocks for the
      NKSP language, which have the following form:
    </p>
    <code>
synchronized

  ??statements??

end synchronized
    </code>
    <p>
      All <code>??statements??</code> which you put into such a synchronized
      code block are guaranteed that they will never get auto suspended by
      the sampler.
    </p>
    <note>
      Such <code>synchronized</code> blocks are a language extension which
      is only available with NKSP. KSP does not support <code>synchronized</code> blocks.
    </note>
    <p>
      So to make our previous example concurrency safe, we would
      change it like this:
    </p>
    <code>
on init
  declare $keysDown
  declare $firstNoteID
  declare $firstNoteNr
  declare $firstVelocity
end on

on note
  { The concurrency sensible code section for the "first active" note. }
  synchronized
    inc($keysDown)
    if ($keysDown = 1 or event_status($firstNoteID) = $EVENT_STATUS_INACTIVE)
      $firstNoteID = $EVENT_ID
      $firstNoteNr = $EVENT_NOTE
      $firstVelocity = $EVENT_VELOCITY
      exit { return from event handler here }
    end if
  end synchronized

  { The non-sensible code for all other subsequent notes would go here. }
end on

on release
  dec($keysDown)
end on
    </code>
    <p>
      If you are already familiar with some programming languages, then you
      might already have seen such synchronized code block concepts
      in languages like e.g. Java. This technique really provides an easy way
      to protect certain sections of your script against concurrency issues.
    </p>
    <note class="important">
      You <b>must</b> use such <code>synchronized</code> code blocks only with great
      care! If the amount of statements being executed in your synchronized block
      is too large, then you will get audio dropouts. If you even use loops in
      synchronized code blocks, then the entire sampler might even become
      unresponsive in case your script is buggy!
    </note>

    <h2>Operators</h2>
    <p>
      A programming language provides so called <i>operators</i> to perform
      certain kinds of transformations of data placed next to the operators.
      These are the operators available with NKSP.
    </p>

    <h3>Arithmetic Operators</h3>
    <p>
      These are the most basic mathematical operators, which allow to add,
      subtract, multiply and divide integer values with each other.
    </p>
    <code>
on init
  message("4 + 3 is " & 4 + 3)        { Add }
  message("4 - 3 is " & 4 - 3)        { Subtract }
  message("4 * 3 is " & 4 * 3)        { Multiply }
  message("35 / 5 is " & 35 / 5)      { Divide }
  message("35 mod 5 is " & 35 mod 5)  { Remainder of Division ("modulo") }
end on
    </code>
    <p>
      You may either use direct integer literal numbers like used in the upper
      example, or you can use integer number variables or integer array variables.
    </p>
    
    <h3>Boolean Operators</h3>
    <p>
      To perform logical transformations of <i>boolean</i> data, you may use the
      following logical operators:
    </p>
    <code>
on init
  message("1 and 1 is " & 1 and 1)  { logical "and" }
  message("1 and 0 is " & 1 and 0)  { logical "and" }
  message("1 or 1 is " & 1 or 1)    { logical "or" }
  message("1 or 0 is " & 1 or 0)    { logical "or" }
  message("not 1 is " & not 1)      { logical "not" }
  message("not 0 is " & not 0)      { logical "not" }
end on
    </code>
    <p>
      Keep in mind that with logical operators shown above,
      all integer values other than <code>0</code>
      are interpreted as boolean <i>true</i> while an integer value of
      precisely <code>0</code> is interpreted as being boolean <i>false</i>.
    </p>
    <p>
      So the logical operators shown above always look at numbers at a whole.
      Sometimes however you might rather need to process numbers bit by bit. For
      that purpose the following bitwise operators exist.
    </p>
    <code>
on init
  message("1 .and. 1 is " & 1 .and. 1)  { bitwise "and" }
  message("1 .and. 0 is " & 1 .and. 0)  { bitwise "and" }
  message("1 .or. 1 is " & 1 .or. 1)    { bitwise "or" }
  message("1 .or. 0 is " & 1 .or. 0)    { bitwise "or" }
  message(".not. 1 is " & .not. 1)      { bitwise "not" }
  message(".not. 0 is " & .not. 0)      { bitwise "not" }
end on
    </code>
    <p>
      Bitwise operators work essentially like logical operators, with the
      difference that bitwise operators compare each bit independently.
      So a bitwise <code>.and.</code> operator for instance takes the 1st bit
      of the left hand's side value, the 1st bit of the right hand's side value,
      compares the two bits logically and then stores that result as 1st bit of
      the final result value, then it takes the 2nd bit of the left hand's side value
      and the 2nd bit of the right hand's side value, compares those two bits logically
      and then stores that result as 2nd bit of the final result value, and so on.
    </p>

    
    <h3>Comparison Operators</h3>
    <p>
      For branches in your program flow, it is often required to compare data
      with each other. This is done by using comparison operators, enumerated
      below.
    </p>
    <code>
on init
  message("Relation 3 < 4 -> " & 3 < 4)    { "smaller than" comparison }
  message("Relation 3 > 4 -> " & 3 > 4)    { "greater than" comparison }
  message("Relation 3 <= 4 -> " & 3 <= 4)  { "smaller or equal than" comparison}
  message("Relation 3 >= 4 -> " & 3 >= 4)  { "greater or equal than" comparison}
  message("Relation 3 # 4 -> " & 3 # 4)    { "not equal to" comparison}
  message("Relation 3 = 4 -> " & 3 = 4)    { "is equal to" comparison}
end on
    </code>
    <p>
      All these operations yield in a <i>boolean</i> result which could then
      be used e.g. with <code>if</code> or <code>while</code> loop statements.
    </p>
    
    <h3>String Operators</h3>
    <p>
      Last but not least, there is exactly one operator for text string data;
      the string concatenation operator <code>&</code>, which
      combines two text strings with each other.
    </p>
    <code>
on init    
  declare @s := "foo" & " bar"
  message(@s)
end on
    </code>
    <p>
      We have used it now frequently in various examples before.
    </p>

    <h2>Preprocessor Statements</h2>
    <p>
      Similar to low-level programming languages like C, C++, Objective C
      and the like, NKSP supports a set of so called preprocessor statements.
      These are essentially "instructions" which are "executed" or rather
      processed, before (and only before) the script is executed by the sampler,
      and even before the script is parsed by the actual NKSP language parser.
      You can think of a preprocessor as a very primitive parser, which is the
      first one getting in touch with your script, it modifies the script code
      if requested by your preprocessor statements in the script, and then
      passes the (probably) modified script to the actual NKSP language parser.
    </p>
    <p>
      When we discussed <a href="#comments">comments</a> in NKSP scripts before,
      it was suggested that you might comment out certain code parts to disable
      them for a while during development of scripts. It was also suggested
      during this language tour that you should not use string variables or use
      the <code>message()</code> function with your final production sounds.
      However those are very handy things during development of your instrument
      scripts. You might even have a bunch of additional code in your scripts
      which only satisfies the purpose to make debugging of your scripts more easy,
      which however wastes on the other hand precious CPU time. So what do you
      do? Like suggested, you could comment out the respective code sections as
      soon as development of your script is completed. But then one day you
      might continue to improve your scripts, and the debugging code would be
      handy, so you would uncomment all the relevant code sections to get them
      back. When you think about this, that might be quite some work each time.
      Fortunately there is an alternative by using preprocessor statements.
    </p>
    
    <h3>Set a Condition</h3>
    <p>
      First you need to set a preprocessor condition in your script. You can do
      that like this:
    </p>
    <code>
SET_CONDITION(??condition-name??)
    </code>
    <p>
      This preprocessor "condition" is just like some kind of
      <i title="A variable which can only have two states: i.e. true or false.">
        boolean variable
      </i>
      which is only available to the preprocessor and by using
      <code>SET_CONDITION(??condition-name??)</code>, this is like setting this
      preprocessor condition to <i>true</i>. Like with regular script
      variables, a preprocessor condition name can be chosen quite arbitrarily
      by you. But again, there are some pre-defined preprocessor conditions
      defined by the sampler for you. So you can only set a condition name here
      which is not already reserved by a built-in preprocessor condition. Also
      you shall not set a condition in your script again if you have already set it
      before somewhere in your script. The NKSP preprocessor will ignore setting
      a condition a 2nd time and will just print a warning when the script is
      loaded, but you should take care of it, because it might be a cause for
      some bug.
    </p>

    <h3>Reset a Condition</h3>
    <p>
      To clear a condition in your script, you might reset the condition like so:
    </p>
    <code>
RESET_CONDITION(??condition-name??)
    </code>
    <p>
      This is like setting that preprocessor condition back to <i>false</i> again.
      You should only reset a preprocessor condition that way if you did set it
      with <code>SET_CONDITION(??condition-name??)</code> before. Trying to
      reset a condition that has not been set before, or trying to reset a
      condition that has already been reset, will both be ignored by the sampler,
      but again you will get a warning, and you should take care about it.
    </p>
    
    <h3>Conditionally Using Code</h3>
    <p>
      Now what do you actually do with such preprocessor conditions? You can use
      them for the NKSP language parser to either
    </p>
    <ul>
      <li>use certain parts of your code</i>
      <li><b>and</b> / <b>or</b> to ignore certain parts of your code</i>
    </ul>
    <p>
      You can achieve that by wrapping NKSP code parts into a pair of either
    </p>
    <code>
USE_CODE_IF(??condition-name??)

  ??some-NKSP-code-goes-here??

END_USE_CODE
    </code>
    <p>
      preprocessor statements, or between
    </p>
    <code>
USE_CODE_IF_NOT(??condition-name??)

  ??some-NKSP-code-goes-here??

END_USE_CODE
    </code>
    <p>
      statements. In the first case, the NKSP code portion is used by the NKSP
      language parser if the given preprocessor <code>??condition-name??</code> is set
      (that is if condition is <i>true</i>).
      If the condition is not set, the NKSP code portion in between is
      completely ignored by the NKSP language parser.
    </p>
    <p>
      In the second case, the NKSP code portion is used by the NKSP
      language parser if the given preprocessor <code>??condition-name??</code> is <b>not</b> set
      (or was reset)
      (that is if condition is <i>false</i>).
      If the condition is set, the NKSP code portion in between is
      completely ignored by the NKSP language parser.
    </p>
    <p>
      Let's look at an example how to use that to define conditional debugging
      code.
    </p>
    <code>
SET_CONDITION(DEBUG_MODE)

on init
  declare const %primes[12] :=  ( 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 )
  declare $i

  USE_CODE_IF(DEBUG_MODE)
  message("This script has just been loaded.")
  
  $i := 0
  while ($i < num_elements(%primes))
    message("Prime " & $i & " is " & %primes[$i])
    $i := $i + 1
  end while
  END_USE_CODE
end on

on note
  USE_CODE_IF(DEBUG_MODE)
  message("Note " & $EVENT_NOTE & " was triggered with velocity " & $EVENT_VELOCITY)
  END_USE_CODE
end on

on release
  USE_CODE_IF(DEBUG_MODE)
  message("Note " & $EVENT_NOTE & " was released with release velocity " & $EVENT_VELOCITY)
  END_USE_CODE
end on

on controller
  USE_CODE_IF(DEBUG_MODE)
  message("MIDI Controller " & $CC_NUM " changed its value to " & %CC[$CC_NUM])
  END_USE_CODE
end on
    </code>
    <p>
      The <i>built-in function</i> <code>num_elements()</code> used above, can
      be called to obtain the size of an array variable at runtime.
      As this script looks now, the debug messages will be printed out. However
      it requires you to just remove the first line, or to comment out the first
      line, in order to disable all debug code portions in just a second:
    </p>
    <code>
{ Setting the condition is commented out, so our DEBUG_MODE is disabled now. }
{ SET_CONDITION(DEBUG_MODE) }

on init
  declare const %primes[12] :=  ( 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 )
  declare $i

  USE_CODE_IF(DEBUG_MODE) { Condition is not set, so this entire block will be ignored now. }
  message("This script has just been loaded.")
  
  $i := 0
  while ($i < num_elements(%primes))
    message("Prime " & $i & " is " & %primes[$i])
    $i := $i + 1
  end while
  END_USE_CODE
end on

on note
  USE_CODE_IF(DEBUG_MODE) { Condition is not set, no message will be printed. }
  message("Note " & $EVENT_NOTE & " was triggered with velocity " & $EVENT_VELOCITY)
  END_USE_CODE
end on

on release
  USE_CODE_IF(DEBUG_MODE) { Condition is not set, no message will be printed. }
  message("Note " & $EVENT_NOTE & " was released with release velocity " & $EVENT_VELOCITY)
  END_USE_CODE
end on

on controller
  USE_CODE_IF(DEBUG_MODE) { Condition is not set, no message will be printed. }
  message("MIDI Controller " & $CC_NUM " changed its value to " & %CC[$CC_NUM])
  END_USE_CODE
end on
    </code>
    <p>
      Now you might say, you could also achieve that by declaring and using
      a regular NKSP variable. That's correct, but there are two major
      advantages by using preprocessor statements.
    </p>
    <ol>
      <li>
        <b>Saving Resources</b> -
        The preprocessor conditions are only processed before the script is
        loaded into the NKSP parser. So in contrast to using NKSP variables,
        the preprocessor solution does not waste any CPU time or memory
        resources while executing the script. That also means that variable
        declarations can be disabled with the preprocessor this way
        and thus will also safe resources.
      </li>
      <li>
        <b>Cross Platform Support</b> -
        Since the code portions filtered out by the preprocessor never make it
        into the NKSP language parser, those filtered code portions might also
        contain code which would have lead to parser errors. For example you
        could use a built-in preprocessor condition to check whether your script
        was loaded into LinuxSampler or rather into another sampler. That way
        you could maintain one script for both platforms: NKSP and KSP.
        Accordingly you could
        also check a built-in variable to obtain the version of the sampler in 
        order to enable or disable code portions of your script that might
        use some newer script features of the sampler which don't exist in older
        version of the sampler.
      </li>
    </ol>
    <p>
      As a rule of thumb: if there are things that you could move from your
      NKSP executed programming code out to the preprocessor, then you should
      use the preprocessor instead for such things. And like stated above,
      there are certain things which you can only achieve with the preprocessor.
    </p>

    <h3>Disable Messages</h3>
    <p>
      Since it is quite common to switch a script between a development version
      and a production version, you actually don't need to wrap all your
      <code>message()</code> calls into preprocessor statements like in the
      previous example just to disable messages. There is actually a built-in
      preprocessor condition dedicated to perform that task much more conveniently for you.
      To disable all messages in your script, simply add <code>SET_CONDITION(NKSP_NO_MESSAGE)</code>
      e.g. at the very beginning of your script.
      So the previous example can be simplified to this:
    </p>
    <code>
{ Enable debug mode, so show all debug messages. }
SET_CONDITION(DEBUG_MODE)

{ If our user declared condition "DEBUG_MODE" is not set ... }
USE_CODE_IF_NOT(DEBUG_MODE)
  { ... then enable this built-in condition to disable all message() calls. }
  SET_CONDITION(NKSP_NO_MESSAGE)
END_USE_CODE

on init
  declare const %primes[12] :=  ( 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 )
  declare $i

  message("This script has just been loaded.")

  USE_CODE_IF(DEBUG_MODE)
  $i := 0
  while ($i < num_elements(%primes))
    message("Prime " & $i & " is " & %primes[$i])
    $i := $i + 1
  end while
  END_USE_CODE
end on

on note
  message("Note " & $EVENT_NOTE & " was triggered with velocity " & $EVENT_VELOCITY)
end on

on release
  message("Note " & $EVENT_NOTE & " was released with release velocity " & $EVENT_VELOCITY)
end on

on controller
  message("MIDI Controller " & $CC_NUM " changed its value to " & %CC[$CC_NUM])
end on
    </code>
    <p>
      You can then actually also add <code>RESET_CONDITION(NKSP_NO_MESSAGE)</code>
      at another section of your script, which will cause all subsequent
      <code>message()</code> calls to be processed again. So that way you can
      easily enable and disable <code>message()</code> calls of entire individual
      sections of your script, without having to wrap all <code>message()</code>
      calls into preprocessor statements.
    </p>

    <h2>What Next?</h2>
    <p>
      You have completed the introduction of the NKSP real-time instrument
      script language at this point. You can now dive into the details of the
      NKSP language by moving on to the
      <a href="nksp_reference.html">NKSP reference documentation</a>.
      Which provides you an overview and quick access to the details of all
      built-in functions, built-in variables and more.
    </p>
    <p>
      You might also be interested to look at new <i>NKSP</i> core language
      features being added to the latest development version of the sampler:
      <a href="real_unit_final/01_nksp_real_unit_final.html">
        Real Numbers, Units and Finalness ...
      </a>
    </p>

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