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49 lines
1.1 KiB
Markdown
49 lines
1.1 KiB
Markdown
5 years ago
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# Simple Dispatch: `case`
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The `case` form dispatches to a clause by matching the result of an
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expression to the values for the clause:
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```racket
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(case expr
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[(datum ...+) body ...+]
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...)
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```
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Each `datum` will be compared to the result of `expr` using `equal?`,
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and then the corresponding `body`s are evaluated. The `case` form can
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dispatch to the correct clause in _O_\(_log N_\)__ time for _N_
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`datum`s.
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Multiple `datum`s can be supplied for each clause, and the corresponding
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`body`s are evaluated if any of the `datum`s match.
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Example:
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```racket
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> (let ([v (random 6)])
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(printf "~a\n" v)
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(case v
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[(0) 'zero]
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[(1) 'one]
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[(2) 'two]
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[(3 4 5) 'many]))
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0
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'zero
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```
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The last clause of a `case` form can use `else`, just like `cond`:
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Example:
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```racket
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> (case (random 6)
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[(0) 'zero]
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[(1) 'one]
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[(2) 'two]
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[else 'many])
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'many
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```
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For more general pattern matching \(but without the dispatch-time
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guarantee\), use `match`, which is introduced in \[missing\].
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