▼Scheme Utilities in (planet cce/ scheme: 7: 4)
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6 Pattern Matching

 (require (planet cce/scheme:7:4/match))

This module provides tools for pattern matching with match.

(match? val-expr pat ...)
Returns #t if the result of val-expr matches any of pat, and returns #f otherwise.

Examples:

> (match? (list 1 2 3)
    (list a b c)
    (vector x y z))

#t

> (match? (vector 1 2 3)
    (list a b c)
    (vector x y z))

#t

> (match? (+ 1 2 3)
    (list a b c)
    (vector x y z))

#f

(define-struct-pattern pat-id struct-id)
Defines pat-id as a match expander that takes one pattern argument per field of the structure described by struct-id. The resulting match expander recognizes instances of the structure and matches their fields against the corresponding patterns.

Examples:

(define-struct pair [a b] #:transparent)
> (define-struct-pattern both pair)
> (match (make-pair 'left 'right)
    [(both a b) (list a b)])

'(left right)

(as ([lhs-id rhs-expr] ...) pat ...)
As a match expander, binds each lhs-id as a pattern variable with the result value of rhs-expr, and continues matching each subsequent pat.

Example:

> (match (list 1 2 3)
    [(as ([a 0]) (list b c d)) (list a b c d)])

'(0 1 2 3)

($ struct-id expr ...)
($ struct-id pat ...)
As an expression, constructs an instance of the structure described by struct-id with fields specified by each expr.

As a match expander, matches instances of the structure described by struct-id with fields matched by each pat.

Examples:

(define-struct pair [a b] #:transparent)
> ($ pair 1 2)

(pair 1 2)

> (match ($ pair 1 2)
    [($ pair a b) (list a b)])

'(1 2)

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