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The following high-order functions
are well-known in functional programming and
most FP libraries provide most of them, or equivalents.
fun curry f x y = f(x,y)
and uncurry f(x,y) = f x y
and map f [] = []
| map f (x::xs) = (f x)::(map f xs)
and foldl f z [] = z
| foldl f z (x::xs) = foldl f (f(z,x)) xs
(* BTW the opr, f, is curried in the Haskell version *)
and foldr f z [] = z
| foldr f z (x::xs) = f(z, (foldr f z xs))
val sum = foldl (op +) 0
and product = foldl (op * ) 1;
(* ------------------------------------------tests-- *)
val l=[1,2,3,4]; sum l; product l;
(* well known high order fns. LA, CSSE, 22/6/2005 *)
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Exercises
- Which of the following are legal, and if so what is the type,
or illegal, and if so why?
- curry curry
- curry uncurry
- uncurry curry
- uncurry uncurry
- Rewrite foldl and foldr
so that parameter f is curried, and rewrite
sum and product to match.
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www #ad:
SML:
| :: | cons |
| [x1,...] | list |
| [ ] | list |
| @ | append |
| fn => | &lambda . |
| : | has type |
Compared
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