[Caml-list] pa_macro to substitute a constant?

[Caml-list] pa_macro to substitute a constant?

[Richard Jones]

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How can I use pa_macro to substitute in a constant into a program?

A real example:

Makefile ------------------------------------------------------------

PACKAGE = foo
VERSION = 1.0.0

version.cmo: version.ml Makefile
	ocamlc -I +camlp4 -pp 'camlp4o pa_macro.cmo -DPACKAGE="$(PACKAGE)" -DVERSION="$(VERSION)"' $< -o $@

version.ml ----------------------------------------------------------

let package = PACKAGE
let version = VERSION

---------------------------------------------------------------------

Needless to say this example doesn't work, and looking at the thin
documentation for pa_macro, I'm not even sure it's possible.  Is it?

Rich.

-- 
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Re: [Caml-list] pa_macro to substitute a constant?

[Michel Mauny]

Richard Jones wrote/écrivait (Fri, Aug 27, 2004 at 05:32:32PM +0100):

> How can I use pa_macro to substitute in a constant into a program?

 > ocamlc -I +camlp4 -pp 'camlp4o pa_macro.cmo -D "PACKAGE="$(PACKAGE)"

> Needless to say this example doesn't work, and looking at the thin
> documentation for pa_macro, I'm not even sure it's possible.  Is it?

I'm afraid not. The "-D" option to pa_macro is followed by an UIDENT,
there is no room for a value for it: in pa_macro.ml, there are two
lines saying

    Pcaml.add_option "-D" (Arg.String (define None))
      "<string> Define for IFDEF instruction."

and the None means "no associated value", here.

However, allowing -D "UIDENT=something" looks like a feature wish I
could try to implement for a future OCaml major release.

-- Michel Mauny

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