Curry: An Integrated Functional Logic Language

A Example Programs
This section contains a few example programs together with some initial expressions and their
computed results.
A.1 Operations on Lists
Here are simple operations on lists. Note that, due to the logic programming features of Curry,
append can be used to split lists. We exploit this property to define the last element of a list in a
very simple way.
-- Concatenation of two lists:
append :: [t] -> [t] -> [t]
append [] ys = ys
append (x:xs) ys = x:append xs ys
-- Naive reverse of all list elements:
rev :: [t] -> [t]
rev [] = []
rev (x:xs) = append (rev xs) [x]
-- Last element of a list:
last :: [t] -> t
last xs | append _ [x] =:= xs = x where x free
Expressions and their evaluated results:
append [0,1] [2,3] ❀ [0,1,2,3]
append L M =:= [0,1]
❀ {L=[],M=[0,1]} | {L=[0],M=[1]} | {L=[0,1],M=[]}
rev [0,1,2,3] ❀ [3,2,1,0]
last (append [1,2] [3,4]) ❀ 4
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