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Scheme / Control Flow

when and unless patterns

Learn when and unless patterns in Scheme with a construct-specific explanation, unique example, engineering boundary, and mastery check.

10 min read • Beginner

when and unless patterns is a focused Scheme topic inside Control Flow. This lesson explains the construct itself, the state or value it operates on, and the observable result it produces.

Read the example as a small executable experiment. Identify the exact syntax that belongs to when and unless patterns, then change one input and predict the result before running it.

Topic-specific example

scheme-02-06-when-and-unless-patterns.scm
scheme Try It Live 
(define ready? #t)
(when ready? (display "go"))
(unless ready? (display "wait"))
Edge case / engineering note

when and unless patterns has rules that are easy to miss when the example is copied mechanically. Check the feature-specific boundary shown by this construct: scope, mutability, evaluation order, type constraints, lifetime, error behavior, compile-time restrictions, or resource cleanup where applicable.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

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