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Re: Command producing several targets at once


From: Thomas Martitz
Subject: Re: Command producing several targets at once
Date: Wed, 26 Jul 2017 14:57:59 +0200

Am 26.07.2017 um 09:24 schrieb Sébastien Hinderer:
Dear all,

OCaml's parser generator, ocamlyacc, produces two files simultaneously.
For example, the command

ocamlyacc parsermly

will produce both parser.ml (the code of the parser) and parser.mli (the
interface of the parsing module, descrbing which symbols it exports).

I am wondering what's the best way to let make know about this.

 From what I understand, a rule like

parser.mli parser.ml: parser.mly
            ocaplyacc $<

does nos say exactly this but is rather an abbreviation for

parser.mli: parser.mly
             ocamlyacc $<

parser.ml: parser.mly
             ocamlyacc $<

which is not what I'd like to express

I have been told that one way to make things work could be the two
following rules:

parser.mli parser.ml: parser.mly
            ocamlyacc $<

parser.mli: parser.ml

Is this the commonly used way to achieve the expected result?

I find it a bit tricky because "parser.mli: parser.ml" looks like a hack
to me, there is no real dependency.

Even if that is what is commonly used, I am wondering how this would
generalize to a command that would produce n files where n>2.

Many thanks for any comment,

Sébastien.


Use pattern rules for this. As a special behavior they run the command only once if multiple targets match the pattern:

%.mli %.ml: %.mly
           ocaplyacc $<


This behavior is different from normal, multi-target rules, and is implement for this very case. See https://www.gnu.org/software/make/manual/make.html#Pattern-Examples

Best gerads.




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