2.13 Dispatch: case

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2 | Syntactic Forms
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5 | Classes and Objects
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▼ | 2 | Syntactic Forms

2.1 | Modules: module, ...
2.2 | Importing and Exporting: require and provide
2.3 | Literals: quote and #%datum
2.4 | Expression Wrapper: #%expression
2.5 | Variable References and #%top
2.6 | Locations: #%variable-reference
2.7 | Procedure Applications and #%app
2.8 | Procedure Expressions: lambda and case-lambda
2.9 | Local Binding: let, let*, letrec, ...
2.10 | Local Definitions: local
2.11 | Constructing Graphs: shared
2.12 | Conditionals: if, cond, and, and or
2.13 | Dispatch: case
2.14 | Definitions: define, define-syntax, ...
2.15 | Sequencing: begin, begin0, and begin-for-syntax
2.16 | Guarded Evaluation: when and unless
2.17 | Assignment: set! and set!-values
2.18 | Iterations and Comprehensions: for, for/ list, ...
2.19 | Continuation Marks: with-continuation-mark
2.20 | Quasiquoting: quasiquote, unquote, and unquote-splicing
2.21 | Syntax Quoting: quote-syntax
2.22 | Interaction Wrapper: #%top-interaction
2.23 | Limiting Scope: define-package, open-package, ...
2.24 | Blocks: block
2.25 | Internal-Definition Limiting: #%stratified-body

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case

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#### 2.13`` Dispatch: case

( case val-expr case-clause ...)

case-clause |  | = |  | [(datum ...) then-expr ...+]
|  | | |  | [ else then-expr ...+]

Evaluates val-expr and uses the result to select a case-clause. The selected clause is the first one with a datum whose quoted form is eqv? to the result of val-expr. If no such datum is present, the else case-clause is selected; if no else case-clause is present, either, then the result of the case form is #<void>.

For the selected case-clause, the results of the last then-expr, which is in tail position with respect to the case form, are the results for the whole case form.

A case-clause that starts with else must be the last case-clause.

Examples:

> ( case (+ 7 5)
[(1 2 3) 'small]
[(10 11 12) 'big])

'big

> ( case (- 7 5)
[(1 2 3) 'small]
[(10 11 12) 'big])

'small

( define (classify c)
( case ( char-general-category c)
[(ll lu lt ln lo) "letter"]
[(nd nl no) "number"]
[ else "other"]))

> (classify #\A)
"letter"
> (classify #\1)
"number"
> (classify #\!)
"other"

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