Re: [Caml-list] How to avoid compiling some code (like #ifdef in C)

[Xavier Leroy <xavier.leroy@inria.fr>]

> --begin--
> open Printf
> 
> let compile_code = false
> 
> let a () = printf "toto\n"
> 
> let _ = if compile_code then let t = 1 in a ()
> --end--
> 
> In above code, if compile_code is true, then the auto-test is executed,
> otherwise not. But if compile_code is false, is the code corresponding
> to 'let t = 1 in a ()' generated?

With ocamlopt, that code is eliminated as part of constant
propagation.

With ocamlc, the code of "let t = 1 in a()" is generated.

> Does anybody see a better approach to do such a thing?

Others mentioned preprocessing with the tool of your choice.  Camlp4
can do #ifdef-style conditional compilation, but in a pinch you can
even use cpp as your preprocessor.

Whether this is a "better" approach is open to debate.  With a
preprocessor, you can remove not just code for expressions, but also
other kind of code, e.g. code for the toplevel binding "let a() = ...".
So, you get more flexibility, but at the expense of less static
checking.  In particular, code that is #ifdef-ed out is not
type-checked, while it is type-checked in your solution above.

- Xavier Leroy

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