1.1.7 Scheme conditionals


if

Scheme has an if procedure:

(if test-expression true-expression false-expression)

test-expression is an expression that returns a boolean value. If test-expression returns #t, the if procedure returns the value of true-expression, otherwise it returns the value of false-expression.

 
guile> (define a 3)
guile> (define b 5)
guile> (if (> a b) "a is greater than b" "a is not greater than b")
"a is not greater than b"

cond

Another conditional procedure in scheme is cond:

(cond (test-expression-1 result-expression-sequence-1)
      (test-expression-2 result-expression-sequence-2)
      …
      (test-expression-n result-expression-sequence-n))

For example:

 
guile> (define a 6)
guile> (define b 8)
guile> (cond ((< a b) "a is less than b")
...          ((= a b) "a equals b")
...          ((> a b) "a is greater than b"))
"a is less than b"

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