Compiling to Executables


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Idris 2 (the language) is designed to be independent of any specific code generator. Still, since the point of writing a program is to be able to run it, it’s important to know how to do so! By default, Idris compiles to executables via Chez Scheme.

You can compile to an executable as follows, at the REPL:

Main> :c execname expr

…where execname is the name of the executable file to generate, and expr is the Idris expression which will be executed. expr must have type IO (). This will result in an executable file execname, in a directory build/exec, relative to the current working directory.

You can also execute expressions directly:

Main> :exec expr

Again, expr must have type IO ().

Finally, you can compile to an executable from the command line by adding the -o <output file> option:

$ idris2 hello.idr -o hello

This will compile the expression Main.main, generating an executable hello (with an extension depending on the code generator) in the build/exec directory.

By default, Idris 2 is a whole program compiler - that is, it finds all the necessary function definitions and compiles them only when you build an executable. This gives plenty of optimisation opportunities, but can also be slow for rebuilding. However, if the backend supports it, you can build modules and executables incrementally:

If the backend supports it, you can generate profiling data by setting the profile flag, either by starting Idris with --profile, or running :set profile at the REPL. The profile data generated will depend on the back end you are using. Currently, the Chez and Racket back ends support generating profile data.

There are five code generators provided in Idris 2, and there is a system for plugging in new code generators for a variety of targets. The default is to compile via Chez Scheme, with an alternative via Racket or Gambit. You can set the code generator at the REPL with the :set codegen command, or via the IDRIS2_CG environment variable.

There are also external code generators that aren’t part of the main Idris 2 repository and can be found on Idris 2 wiki:

External backends

There is work in progress support for generating libraries for other languages from idris2 code.