Scheme allows a procedure to return more than one value to its caller. This is quite different to other languages which only allow single-value returns. Returning multiple values is different from returning a list (or pair or vector) of values to the caller, because conceptually not one compound object is returned, but several distinct values.
The primitive procedures for handling multiple values are
values is used for returning
multiple values from a procedure. This is done by placing a call to
values with zero or more arguments in tail position in a
call-with-values combines a procedure returning
multiple values with a procedure which accepts these values as
Delivers all of its arguments to its continuation. Except for continuations created by the
call-with-valuesprocedure, all continuations take exactly one value. The effect of passing no value or more than one value to continuations that were not created by
scm_values, args is a list of arguments and the return is a multiple-values object which the caller can return. In the current implementation that object shares structure with args, so args should not be modified subsequently.
Calls its producer argument with no values and a continuation that, when passed some values, calls the consumer procedure with those values as arguments. The continuation for the call to consumer is the continuation of the call to
call-with-values.(call-with-values (lambda () (values 4 5)) (lambda (a b) b)) ⇒ 5(call-with-values * -) ⇒ -1
In addition to the fundamental procedures described above, Guile has a
module which exports a syntax called
receive, which is much
more convenient. This is in the
(ice-9 receive) and is the
same as specified by SRFI-8 (see SRFI-8).
(use-modules (ice-9 receive))
Evaluate the expression expr, and bind the result values (zero or more) to the formal arguments in formals. formals is a list of symbols, like the argument list in a
lambda(see Lambda). After binding the variables, the expressions in body ... are evaluated in order, the return value is the result from the last expression.
For example getting results from
partitionin SRFI-1 (see SRFI-1),(receive (odds evens) (partition odd? '(7 4 2 8 3)) (display odds) (display " and ") (display evens)) -| (7 3) and (4 2 8)