11.3.143 numbervars/3 [meta_logic]

Synopsis

numbervars(+Term, +FirstVar, -LastVar)

instantiates each of the variables in Term to a term of the form '$VAR'(N).

Arguments

Term

term

FirstVar

integer, must be nonvar

LastVar

integer

Description

FirstVar is used as the value of N for the first variable in Term (starting from the left). The second distinct variable in Term is given a value of N satisfying “N is FirstVar+1”; the third distinct variable gets the value FirstVar+2, and so on. The last variable in Term has the value LastVar-1.

Notice that in the example below, display/1 is used rather than write/1. This is because write/1 treats terms of the form '$VAR'(N) specially; it writes ‘A’ if N=0, ‘B’ if N=1, ...‘Z’ if N=25, ‘A1’ if N=26, etc. That is why, if you type the goal in the example below, the variable bindings will also be printed out as follows:

     Term = foo(W,W,X),
     A = W,
     B = X

Exceptions

instantiation_error

FirstVar is uninstantiated

type_error

FirstVar is not an integer

Examples

     | ?- Term = foo(A, A, B), numbervars(Term, 22, _), display(Term).
     foo($VAR(22),$VAR(22),$VAR(23))

See Also

ref-lte-anv, listing/[0,1], write_term/[2,3].