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Like all languages, Scheme provides conditionals. The basic form is the if:

(if test-expression
    then-expression
    else-expression)

If test-expression evaluates to true (ie, any value other than #f), the then-expression is evaluated. If not, the else-expression is evaluated. else-expression is optional.

(if (= (+ 2 3) 5)
    'schemes-addition-works!)
=> schemes-addition-works!

(if (< 3 2)
    'three-is-less-than-two
    'three-isnt-less-than-two)
=> three-isnt-less-than-two

Scheme provides some other conditional forms for convenience. They can all be defined as macros (chap 8) that expand into if-expressions.

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