Re: ML-style pattern matching in C-like languages

> Do you really have to change the language C for this ? Write a
> function which does the matching. Granted, within the limits of C, the
> struct to be matched has to be built up before matching, and this
> takes some lines of code. But would you really sacrifice compatibility
> with C merely for getting some shorthand notation in return ?


Do you have to change the language? Of course not.
But if there were never occasions to change the language, why
aren't all the C++, ML, Java, Python, etc. programmers using C too?


More to the point, why do yacc and lex exist when their functionality
could have been packaged up into a library? One answer might
have been performance (they could do one-time analysis at compile
time to pre-compute the tables used at run time), but that's not
as big an issue on today's machine. The reason they're still around
is convenience. I've written parsers using a yacc library instead
of yacc itself, and it's awful. Compare:


expr: expr "+" expr { $$ = $1 + $3; }


and


static int
yyaction(Yystype *out, Yystype *in)
{
out->f = in[0].f + in[2].f;
}
yyaddrule("expr", yyaction, "expr", "+", "expr", 0);


and then multiply by 100.


Compatibility with C is very important in many contexts and not
something to be thrown away lightly, but if the benefit is significant,
then I think people will go along. It all depends on the context.


Russ

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