Hi all,
I just thought I'd share this with the list. Here is some ugly code in
generic.standard:
: (simplify-alist) ( class i assoc -- default assoc )
2dup length 1- = [
nth second { } rot drop
] [
3dup >r 1+ r> nth first class< [
>r 1+ r> (simplify-alist)
] [
[ nth second ] 2keep swap 1+ tail rot drop
] if
] if ;
: simplify-alist ( class assoc -- default assoc )
dup empty? [
2drop [ "Unreachable" throw ] { }
] [
0 swap (simplify-alist)
] if ;
Here is a refactored version:
: simplify-alist ( class assoc -- default assoc' )
{
{ [ dup empty? ] [ 2drop [ "Unreachable" throw ] { } ] }
{ [ dup length 1 = ] [ nip first second { } ] }
{ [ 2dup second first class< ] [ 1 tail-slice simplify-
alist ] }
{ [ t ] [ nip [ second second ] [ 1 tail-slice ] bi ] }
} cond ;
What changed is that I merged the two words into one, changed the
conditional nesting into one cond, and replaced the i/assoc pair with
a single assoc. When advancing down the list, we do '1 tail-slice' to
chop off the first key/value pair.
Here is an alternative version; instead of using nip in a couple of
places, I use more combinators:
: simplify-alist ( class assoc -- default assoc' )
{
{ [ dup empty? ] [ 2drop [ "Unreachable" throw ] { } ] }
{ [ dup length 1 = ] [ [ drop ] [ first second ] bi* { } ] }
{ [ 2dup second first class< ] [ 1 tail-slice simplify-
alist ] }
{ [ t ] [ [ drop second second ] [ drop 1 tail-slice ] 2bi ] }
} cond ;
The last version does not have any shuffling other than drop, 2drop,
dup, and 2dup.
Slava
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