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**2**- (**download**) (**annotate**)*Sat Oct 4 23:33:09 1997 UTC*(22 years, 6 months ago) by*monnier*File size: 1103 byte(s)

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(* list-xprod.sml * * COPYRIGHT (c) 1993 by AT&T Bell Laboratories. See COPYRIGHT file for details. * * Functions for computing with the cross product of two lists. *) structure ListXProd : LIST_XPROD = struct (* apply a function to the cross product of two lists *) fun appX f (l1, l2) = let fun lp1 [] = () | lp1 (x::r) = let fun lp2 [] = lp1 r | lp2 (y::r) = (f(x, y); lp2 r) in lp2 l2 end in lp1 l1 end (* map a function across the cross product of two lists *) fun mapX f (l1, l2) = let fun lp1 ([], resL) = rev resL | lp1 (x::r, resL) = let fun lp2 ([], resL) = lp1 (r, resL) | lp2 (y::r, resL) = lp2 (r, f(x, y) :: resL) in lp2 (l2, resL) end in lp1 (l1, []) end (* fold a function across the cross product of two lists *) fun foldX f (l1, l2) = let fun lp1 ([], accum) = accum | lp1 (x::r, accum) = let fun lp2 ([], accum) = lp1 (r, accum) | lp2 (y::r, accum) = lp2 (r, f(x, y, accum)) in lp2 (l2, accum) end in fn init => lp1 (l1, init) end end; (* ListXProd *)

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