I've run into the situation a few times now where I've had "a b c" on
the stack, and wanted to perform "a c foo" followed by "b c bar"--
effectively a cleave followed by a spread. I had been doing this to
get that effect:
[ [ foo ] curry ]
[ [ bar ] curry ] bi bi*
This could also work:
[ dup swapd ] 2dip 2bi*
but that double nesting and repeated curry is an eyesore, and swapd is
evil, especially as part of a three-punch shuffling combo. So I threw
the following words into combinators.lib:
: bi, ( obj quot quot -- quot' quot' )
[ [ curry ] curry ] bi@ bi ; inline
: tri, ( obj quot quot quot -- quot' quot' quot' )
[ [ curry ] curry ] tri@ tri ; inline
So you can now say:
[ foo ] [ bar ] bi, bi*
Which reads nicely: "cleave the top value, then spread the next two
values".
Say you have the inverse problem: you have "a b c" on the stack, and
you need to "a b foo" followed by "a c bar". With these words:
: bi*, ( obj obj quot quot -- quot' quot' )
[ [ curry ] curry ] bi@ bi* ; inline
: tri*, ( obj obj obj quot quot quot -- quot' quot' quot' )
[ [ curry ] curry ] tri@ tri* ; inline
you can say:
[ foo ] [ bar ] bi*, bi
"bi@," and "tri@," are also defined.
For the theorists, the nbi/ntri words could be defined as repeated
applications of bi,/tri,:
: 2bi bi, bi ;
: 3bi bi, bi, bi ;
: 4bi bi, bi, bi, bi ; ! etc.
That trick doesn't quite work for nbi*/ntri*/nbi@/ntri@ -- "bi*, bi*"
transposes its arguments relative to "2bi*":
a b c d [ + ] [ - ] 2bi* ! -- a+b c-d
a b c d [ + ] [ - ] bi*, bi* ! -- a+c b-d
That's actually kind of handy, since either stack order could be useful.
-Joe
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