if -- r7rs Definition

§

Kind

§

syntax;

Implemented by

§

• if (from vonuvoli);

Syntax signature

§

Syntax keywords:

• condition: expression;
• then-expression: expression;
• else-expression: expression;

Syntax variants:

• (_ condition then-expression)
• (_ condition then-expression else-expression)

Exports

§

• scheme:base -- (scheme base);

Exports recursive

§

• scheme -- (scheme);

Description

§

(if <test> <consequent> <alternate>)
(if <test> <consequent>)

Syntax: <Test>, <consequent>, and <alternate> are expressions.

Semantics: An if expression is evaluated as follows: first, <test> is evaluated. If it yields a true value (see section on booleans), then <consequent> is evaluated and its values are returned. Otherwise <alternate> is evaluated and its values are returned. If <test> yields a false value and no <alternate> is specified, then the result of the expression is unspecified.

(if (> 3 2) 'yes 'no)           ===>  yes
(if (> 2 3) 'yes 'no)           ===>  no
(if (> 3 2)
    (- 3 2)
    (+ 3 2))                    ===>  1

---

The text herein was sourced and adapted as described in the "R7RS attribution of various text snippets" appendix.