On Sun, 2007-08-26 at 11:13 +1000, skaller wrote:
> On Sat, 2007-08-25 at 17:12 -0700, Erick Tryzelaar wrote:
> If you know the list on the RHS of the -> symbol is non-empty,
> then you can probably do this with a typematch .. something like:
>
> typematch typeof (list (1,2,3)) with
> | list [?t] => ?t
> endmatch
>
>
> looks like it should work .. but probably doesn't.
Well I'll be .....
/////////////////////////////////////////
#import <flx.flxh>
open List;
val a = list(1,2,3);
var b
:
typematch typeof(a) with
| list[?t] => t
endmatch
=
1
;
println b;
///////////////////////////////////////////
Note I HAD to use a 'val' for a. The type of x in
var x = 1;
is actually
lvalue[int]
and not just int, so the typematch fails. Might be worth a
no_lvalues_please_typeof (x)
operator .. with a wrong type you get some message like:
SYSTEM FAILURE
beta-reduce failed in lvalue[(typematch lvalue[(int<1815> -> int<1815>)]
with
| <T5403> -> <T5402> => <T5402>
endmatch)]msg: [beta-reduce] typematch failure
where you would REALLY like: the message to say
"The type of x must be a list, got blah instead"
--
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net
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