Felix rocks. Here's basic comprehensions with parallel iteration that
work on every data structure that implements map and zip. No product
iteration or guards yet. One problem with this though is that zipping
doesn't work across an arbitrary number of items. So, to make this
mostly useful we'd need to provide, say, n=1 through 20 zips. Know of
an easy way to do this?
comprehensions.flx:
/////////////////////////////////
SCHEME """
(define (deflambda sr vars body)
`(ast_lambda ((() ((ast_tuple ()) ()))
((,vars none))
typ_none
((ast_fun_return ,sr ,body)))))
""";
syntax comprehensions {
satom := lsqb sexpr vbar comp_parameters rsqb =>#
"""
`(ast_apply ,_sr
((ast_apply ,_sr
((ast_name "map" () )
,(deflambda _sr (car _4) _2)))
,(cadr _4)))
""";
comp_parameters := comp_parameter (vbar comp_parameter)* =>#
"""
(list (cons (car _1) (map caadr _2))
`(ast_apply ,_sr
((ast_name "zip" ())
,(cons (cadr _1) (map cdadr _2))))))
""";
comp_parameter := sparameter <- sexpr =># "(list _1 _3)";
}
/////////////////////////////////
foo.flx:
/////////////////////////////////
#import <flx.flxh>
#syntax <comprehensions.flx>
open syntax comprehensions;
open List;
instance[T,U with Show[T], Show[U]] Str[T*U] {
fun str (x:T, y:U):string =>
'(' + (repr x) + ', ' + (repr y) + ')'
;
}
open[T,U] Str[T*U];
fun zip[T] (xs:list[T]) => xs;
fun zip[T,U] (xs:list[T], ys:list[U]) : list[T*U] = {
fun aux (xs:list[T]) (ys:list[U]) (acc:list[T*U]) =>
match xs, ys with
| Empty[T], _ => acc
| _, Empty[U] => acc
| Cons (?x, ?xs), Cons (?y, ?ys) => aux xs ys ((x, y) + acc)
endmatch
;
return rev $ aux xs ys Empty[T*U];
}
val xs = list(1,2,3);
val ys = list(4,5,6);
val zs = [ x * y | x:int <- xs | y:int <- ys ];
println xs;
println ys;
println zs;
/////////////////////////////////
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