19 Match utilities

(require (planet untyped/unlib/match))

Additional patterns for use in scheme/match expressions like match and match-lambda.

(eq? expr pattern ...)

Binds values that are eq? to expr. Behaves similarly to the built-in ? pattern: if the eq? pattern matches, the other patterns are also matched against the same value.

Examples:

> (define x 123)

> (define eq-to-x?       (match-lambda         [(eq? x y)          (format "yes: ~a" y)]         [_ "no"]))

> (eq-to-x? 123)

"yes: 123"

> (eq-to-x? 234)

"no"

(equal? expr pattern ...)

Binds values that are equal? to expr. Behaves similarly to the built-in ? pattern: if the equal? pattern matches, the other patterns are also matched against the same value.

Examples:

> (define x "123")

> (define equal-to-x?       (match-lambda         [(equal? x y)          (format "yes: ~a" y)]         [_ "no"]))

> (equal-to-x? "123")

"yes: 123"

> (equal-to-x? "456")

"no"