Curry: An Integrated Functional Logic Language

g :: [a] -> [b] -> ([a],[b])
g x y = (f x, f y)
h :: ([Int],[Bool])
h = g [3,4] [True,False]
However, if the type declaration for g is omitted, the usual type inference algorithms are not able
to infer this type.
5 Expressions
Expressions are a fundamental notion of Curry. As introduced in Section 2, functions are defined
by equations defining expressions that are equivalent to specific function calls. For instance, the
program rule
square x = x*x
defines that the function call (square 3) is equivalent to the expression (3*3).
Expressions occur in conditions and right-hand sides of equations defining functions. A computation
evaluates an expression to a data term (see Section 3). Expressions are built from constants
of a specific data type (e.g., integer constants, character constants, see Section 4), variables, or applications
of constructors or functions to expressions. Furthermore, Curry provides some syntactic
extensions for expressions that are discussed in this section.
5.1 Arithmetic Sequences
Curry supports two syntactic extensions to define list of elements in a compact way. The first one
is a notation for arithmetic sequences. The arithmetic sequence
[ e1 , e2 .. e3 ]
denotes a list of integers starting with the first two elements e1 and e2 and ending with the element
e3 (where e2 and e3 can be omitted). The precise meaning of this notation is defined by the
following translation rules:
Arithmetic sequence notation: Equivalent to:
[e .. ] enumFrom e
[e1,e2 .. ] enumFromThen e1 e2
[e1 .. e2] enumFromTo e1 e2
[e1,e2 .. e3] enumFromThenTo e1 e2 e3
The functions for generating the arithmetic sequences, enumFrom, enumFromThen, enumFromTo, and
enumFromThenTo, are defined in the prelude (see page 53). Thus, the different notations have the
following meaning:
• The sequence [e..] denotes the infinite list [e,e+1,e+2,...].
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