On Wed, 2006-10-04 at 20:41 -0700, Erick Tryzelaar wrote:
> A minor problem I ran into while playing around with the testing of the
> stdlib. I'd like to be able to insert debugging code into a pattern
> match, but in order to do that, I have to make everything into an
> anonymous function. I wish I could do something like this:
>
> fun map[T,U] (f:T->U) (x:list[T]) =>
> match x with
> | Empty[T] => Empty[U]
> | Cons(?h, ?t) =>
> print "hello"; endl;
> Cons(_f h, map f x)
> endmatch
> ;
The problem is the RHS of => must be an expression. So what you
want in the first instance is a function like:
fun second[t] (a:unit,b:t):t => b
which ignores the first argument and returns the second one.
Then you could write
second$ { print "Debug"; return (); } (), b
Of course, there's a risk Felix will elide the call to
the useless first argument, but that's easy to fix
with a C hack:
fun second[t]: (1->0) * t ->t = "run ($1),$2";
where somehow 'run $1' runs a procedure closure.
(there's a Felix function to do that in the library
but no C function .. I need to fix that).
--
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net
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