Re: patterns

On Tue, 15 Oct 2002 [email protected] wrote:
>
> After reading the cons manual, I still can't figure out how to write a
> simple pattern rule in Cons. For instance, if I want to create a "ps"
> file from a "dvi" file using dvips, in GNU Make I can write the
> following rule:
>
> %.ps: %.dvi
>         dvips $< -o $@
>

Cons has no "implicit rules" ala make (pattern matching rules/suffix rules).
I think this is very *good*. Even if the implicit choosing of rules
in make is tempting in the simple case, I've seen too many cases
where *the wrong* rule is choosen by "accident" and the poor
ordinary make user has no clue what is happening.

A Construct instead explicitly tells Cons what there is to build.
But since you have a real programming language at your disposal
the difference isn't so big. Just create a "dvips" method ...


> Is there a way to do this easily in cons?
>

You could do something like:

      #--------------------------------------------------
      sub cons::dvi2ps
      {
	  my ($e, $dvi) = @_;

	  # replace suffix: .dvi ---> .ps
	  my $ps = $dvi;
	  $ps =~ s/\.dvi$//;
	  $ps .= ".ps";

	  $e->Command( $ps, $dvi, "dvips %< -o %>");
      }

      $e = cons->new();

      # use the new method ...
      $e->dvi2ps( "foo.dvi" );

      #--------------------------------------------------

And if you intent do use this more than once, you can move the
"cons::dvi2ps" method into a Perl-module and just add a "use" line
like below to your Construct file:

      use YourConsStuff;

      $e = cons->new();
      $e->dvi2ps( "foo.dvi" );

Or maybe even make a sub-class of "cons" and add the method there.

In either case you get a rather short Construct file.

/Johan Holmberg



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