if

performs simple branching

Usage: (if pred then else?)

If the evaluated predicate is truthy (not #f (false) or the empty list), the then form is evaluated and returned, otherwise the else form, if any, will be evaluated and returned.

An Example

(define x '(1 2 3 4 5 6 7 8))

(if (> (length x) 3)
    "x is big"
    "x is small")

If the symbol unless is used instead of if, then the logical branching will be inverted.