Racket Code Generator

Racket Code Generator#

The Racket code generator is accessed via a REPL command:

Main> :set cg racket

Alternatively, you can set it via the IDRIS2_CG environment variable:

$ export IDRIS2_CG=racket

You can compile an expression expr of type IO () to an executable as follows, at the REPL:

Main> :c execname expr

…where execname is the name of the executable file. This will generate the following:

  • A shell script build/exec/execname which invokes the program

  • A subdirectory build/exec/execname_app which contains all the data necessary to run the program. This includes the Racket source (execname.rkt), the compiled Racket code (execname or execname.exe on Windows) and any shared libraries needed for foreign function definitions.

The executable execname is relocatable to any subdirectory, provided that execname_app is also in the same subdirectory.

You can also execute an expression directly:

Main> :exec expr

Again, expr must have type IO (). This will generate a temporary executable script _tmpracket in the build/exec directory, and execute that, without compiling to a binary first (so the resulting Racket code is interpreted).

Racket Directives#

  • --directive extraRuntime=<path>

    Embed Scheme source from <path> directly into generated output. Can be specified more than once, in which case all given files will be included in the order specified.

    ; extensions.scm
(define (my-mul a b)
  (* a b))

    -- Main.idr
%foreign "scheme:my-mul"
myMul : Int -> Int -> Int

    $ idris2 --codegen chez --directive extraRuntime=/path/to/extensions.scm -o main Main.idr

  • --directive lazy=weakMemo

    Makes all non-toplevel Lazy and Inf values to be weakly memoised. That is, once this expression is evaluated at runtime, it is allowed to not to be recalculated on later accesses until memoised value is wiped by a garbage collector. Garbage collector is allowed to collect weakly memoised values at its own discretion, so when no free memory is available, weakly memoised values are free to be wiped. That’s why it is safer comparing to full memoisation.

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