Chez Scheme Code Generator

The Chez Scheme code generator is the default, or it can be accessed via a REPL command:

Main> :set cg chez

By default, therefore, to run Idris programs you will need to install Chez Scheme. Chez Scheme is open source, and available via most OS package managers.

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 Chez Scheme source (, the compiled Chez Scheme code ( 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 _tmpchez in the build/exec directory, and execute that.

Chez Scheme is the default code generator, so if you invoke idris2 with the -o execname flag, it will generate an executable script build/exec/execname, again with support files in build/exec/execname_app.

Chez 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