Oh YES! Here we go (takes AGES to compile but it works):
//////////////////
include "std/datatype/ralist";
open Ralist;
fun _match_ctor_Cons[T] (x:ralist[T]) =>not ( ralist_empty x);
fun _match_ctor_Empty[T] (x:ralist[T]) => ralist_empty x;
fun _ctor_arg_Cons[T] (x:ralist[T]) : T * ralist[T] =
{
var elt : T;
var tail : ralist[T];
ralist_uncons (x, &elt, &tail);
return elt,tail;
}
var x : ralist[int] = RAnil[int];
x = ralist_cons (1, x);
x = ralist_cons (2, x);
x = ralist_cons (4, x);
x = ralist_cons (9, x);
x = ralist_cons (16, x);
println$ "List=" + x.str;
match x with
| Cons (?elt, Cons (?elt2, ?tail)) =>
println$ "Head1="+ elt.str + "Second=",+elt2.str + ", Tail="+ tail.str;
| Cons (?elt, ?tail) =>
println$ "Head="+ elt.str + ", Tail="+ tail.str;
| Empty =>
println$ "Empty list";
endmatch;
/////////////////
~/felix>build/release/host/bin/flx --test=build/release ta
List=16,9,4,2,1
Head1=16, Second=9, Tail=4,2,1
/////////////////
Note, we even overloaded the standard list constructor names so
the patten match code is textually identical to the code for a standard list.
And that nested pattern matches work too!
Also note the match checkers and extractor are defined
with Felix code (not with bindings to C++). Polymorphism even
seems to work :)
You may be curious why I'm so ecstatic about this.
That's because you haven't grokked exactly how powerful this mechanism is.
Consider for example ..
* Modelling regexps as pattern matches
or try this:
match s with
| Split (?left, ?right) => ...
the point of which is:
| Split (?left, Split (?middle, ?right)) =>
Writing that procedurally:
var left, tmp = split s;
var middle, right = split tmp;
which sucks by comparison (note .. Ieft out the check if the split worked?)
--
john skaller
skal...@users.sourceforge.net
http://felix-lang.org
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