Hello,
In combinators.lib, we have &&, ||, and some arity variants. However, they
only return 't' or 'f'. We're interested in versions which return non-f
results. In the case of '||' it would return the first non-f result. In the
case of '&&' it would return the last result if all the results were non-f.
If you perform a manual expansion of expressions which you'd pass to &&
and ||, a pattern arises. I think this macro captures the 0 arity case:
: 0||-rewrite ( quots -- quot )
dup empty?
[ drop [ ] ]
[ unclip swap 0||-rewrite '[ drop @ dup [ ] [ @ ] if ] ]
if ;
MACRO: 0|| ( quots -- quot ) 0||-rewrite f prefix ;
This is 1 arity case:
: 1||-rewrite ( quots -- quot )
dup empty?
[ drop [ nip ] ]
[ unclip swap 1||-rewrite '[ drop dup @ dup [ nip ] [ @ ] if ] ]
if ;
MACRO: 1|| ( quots -- quot ) 1||-rewrite f prefix ;
And finally the 2 arity case:
: 2||-rewrite ( quots -- quot )
dup empty?
[ drop [ 2nip ] ]
[ unclip swap 2||-rewrite '[ drop 2dup @ dup [ 2nip ] [ @ ] if ] ]
if ;
MACRO: 2|| ( quots -- quot ) 2||-rewrite f prefix ;
Fry really helped here. I'm the syntax rebel/separatist around here. I'd been
experimenting with a syntax I call "auto fry" whereby you don't have to
single-quot a quotation in order to fry it. If a quotation contains fry
directives, it's fried. I really like this but this in this application it
didn't work. I was using auto-fry instead of the explicit fry above. The
probem is, the quotation I intend to fry is actually in another quotation.
The inner directives cause the outer quotation to fry; not the desired
result...
Ed
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