Reference: PLT Scheme

1`` | Language Model
2`` | Syntactic Forms
3`` | Datatypes
4`` | Structures
5`` | Classes and Objects
6`` | Units
7`` | Contracts
8`` | Pattern Matching
9`` | Control Flow
10`` | Concurrency
11`` | Macros
12`` | Input and Output
13`` | Reflection and Security
14`` | Operating System
15`` | Memory Management
16`` | Running PLT Scheme
| Bibliography
| Index

On this page:

case

Version: 4.0.2
contents index
← prev up next →

#### 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"

contents index
← prev up next →