(r5rs.info.gz) Procedures
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4.1.4 Procedures
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-- syntax: lambda <formals> <body>
_Syntax:_ <Formals> should be a formal arguments list as described
below, and <body> should be a sequence of one or more expressions.
_Semantics:_ A lambda expression evaluates to a procedure. The
environment in effect when the lambda expression was evaluated is
remembered as part of the procedure. When the procedure is later
called with some actual arguments, the environment in which the
lambda expression was evaluated will be extended by binding the
variables in the formal argument list to fresh locations, the
corresponding actual argument values will be stored in those
locations, and the expressions in the body of the lambda expression
will be evaluated sequentially in the extended environment. The
result(s) of the last expression in the body will be returned as
the result(s) of the procedure call.
(lambda (x) (+ x x)) ==> __a procedure
((lambda (x) (+ x x)) 4) ==> 8
(define reverse-subtract
(lambda (x y) (- y x)))
(reverse-subtract 7 10) ==> 3
(define add4
(let ((x 4))
(lambda (y) (+ x y))))
(add4 6) ==> 10
<Formals> should have one of the following forms:
* (<variable1> ...,): The procedure takes a fixed number of
arguments; when the procedure is called, the arguments will
be stored in the bindings of the corresponding variables.
* <variable>: The procedure takes any number of arguments; when
the procedure is called, the sequence of actual arguments is
converted into a newly allocated list, and the list is stored
in the binding of the <variable>.
* (<variable1> ..., <variable_n> . <variable_n+1>): If a
space-delimited period precedes the last variable, then the
procedure takes n or more arguments, where n is the number of
formal arguments before the period (there must be at least
one). The value stored in the binding of the last variable
will be a newly allocated list of the actual arguments left
over after all the other actual arguments have been matched
up against the other formal arguments.
It is an error for a <variable> to appear more than once in
<formals>.
((lambda x x) 3 4 5 6) ==> (3 4 5 6)
((lambda (x y . z) z)
3 4 5 6) ==> (5 6)
Each procedure created as the result of evaluating a lambda
expression is (conceptually) tagged with a storage location, in
order to make `eqv?' and `eq?' work on procedures (see section
Equivalence predicates).
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