same_key_prefix(+Key, +All, -KeyVal, -Prefix, -Rest)

Key

Key argument position (non-negative integer, or list of those)

All

List of structures

KeyVal

Variable, or common key

Prefix

Variable, or list of structures

Rest

Variable, or list of structures

Description

The list All is split into two sublists Prefix and Rest, such that Prefix contains all the leading elements of All whose Key arguments are identical (in the sense of ==/2), and Rest contains the remainder of the list. Concatenating the Prefix and Rest will yield the original list All. The key value of the Prefix is returned as KeyVal.

Modes and Determinism

• same_key_prefix(+, +, -, -, -) is semidet

Fail Conditions

Exceptions

(4) instantiation fault

Arguments are insufficiently instantiated

(5) type error

Some argument or its components are of the wrong type

(6) out of range

Some structure does not have a Key'th argument

Examples

    ?- same_key_prefix(1, [f(a,1),f(a,2),f(c,3),f(b,4),f(a,5)],
                       KeyVal, Prefix, Rest).
    KeyVal = a
    Prefix = [f(a,1), f(a,2)]
    Rest = [f(c,3), f(b,4), f(a,5)]
    Yes (0.00s cpu)

    ?- same_key_prefix(1, [], KeyVal, Prefix, Rest).
    No (0.00s cpu)

See Also