EEL2 preprocessor

EEL2 preprocessor

The EEL2 preprocessor expands compile-time directives like #include, #define, and conditional compilation before the JSFX source is parsed.

Kind: concept

JSFX (and ReaScript/EEL) in REAPER v6.74+ support the EEL2 preprocessor, which allows generating EEL2 code at compile-time. To make effecient JSFX/EEL2 code, it is often helpful to use named variables rather than memory, and when using a lot of variables it is often harder to write and maintain. The EEL2 preprocessor allows you to generate repetitive code dynamically.

To use the EEL2 preprocessor, one uses the tags in EEL2 code. Between these tags, a separate EEL2 compiler runs, using a minimal, separate, and non-persistent state, and can generate EEL2 code output using the printf() function.

Additionally, preprocessor code can suppress passthrough of existing text between its blocks by setting the _suppress variable (allowing for conditional compilation).

Examples

Suppose you have state consisting of 16 values and you wish to clear that state:

  x00=0; x01=0; x02=0; x03=0; x04=0; x05=0; x06=0; x07=0;
  x08=0; x09=0; x10=0; x11=0; x12=0; x13=0; x14=0; x15=0;

Using the EEL2 preprocessor, you could write this as:

  <? x_size = 16; /* near the start of file, perhaps */ ?>

  ...

  <?
     // x_size will still be set
     loop(i=0;x_size, printf("x%02d=0;\n", i); i += 1);
  ?>

To use _suppress for conditional compilation, one does something along the lines of:

  <? some_config = 1; ?>

  ...

  <? some_config < 5 ? _suppress = 1; ?>

  do_some_extra_code() // only compiled if some_config is >= 5
  ...

  <? _suppress = 0; ?>

Note that in the preprocessor the only functions available are built-in EEL2 math/logic functions, and printf(). REAPER 6.82+ also supports include(), which allows JSFX to include additional EEL2 files inline (rather than @import which imports the file and its JSFX sections).