Scheme (programming language): Difference between revisions

Revision as of 02:04, 24 May 2003

Revision as of 22:49, 27 May 2003

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(else exprn))

The first expression for which the test evaluates to true (anything other than #tf counts as true) will be evaluated. If notall test resultsresult in #tf, the else clause is evaluated.

A variant of the cond clause is

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...)

In this case, expr should beevaluate to a function that takes one argument. If test evaluates to #ttrue, the function is called with the return value of test.

Scheme also has

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==== Loops ====

Loops in Scheme usually take the form of tail recursion. A classical example is the factorial function, which can be defined non-tail-recursively:

(define (factorial n)

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;; => 120

or a higher order function like ''map'' which applies a function to every element of a list, and can be defined non-tail-recursively:

(define (map f lst)

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;; => (1 4 9 16)

AnotherWe way tocan define loopsboth isof thethese trail recursively as follows. The ''named'' <code>let</code> statement and the <code>do</code> statement are syntactic sugar which simpify tail recursive definitions. To use factorial and map again to illustrate both forms:

(define (factorial n)

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;; => (1 4 9 16)

Please note that in both cases, the tail recursive version is preferrable due to its decreased use of space.

=== Input/output ===