Version: 4.1
2.16 Guarded Evaluation: when and unless
Effects If...: when and unless in Guide: PLT Scheme introduces when and unless.
(when test-expr expr ) |
Evaluates the text-expr. If the result is #f, then the result of the when expression is #<void>. Otherwise, the exprs are evaluated, and the last expr is in tail position with respect to the when form.
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hi there |
(unless test-expr expr ) |
Equivalent to (when (not test-expr) expr ).
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hi there |