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JSFX Programming Reference - EEL2 Preprocessor
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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 <? and ?> 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).
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().