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- ; Part of Scheme 48 1.9. See file COPYING for notices and license.
- ; Authors: Richard Kelsey, Jonathan Rees
- ; A version of LET and LET* which allows clauses that return multiple values.
- ;
- ; MV = multiple-value
- ;
- ; (mvlet (<clause> ...) <body>)
- ; (mvlet* (<clause> ...) <body>)
- ;
- ; <clause> ::= (<ids> <expression>)
- ; <ids> ::= <id> | (<id> ...) | (<id> ... . <id>)
- ;
- ; A clause of the form (<id> <exp>) is like a normal LET clause. There is no
- ; clause equivalent to
- ; (call-with-values (lambda () <expression>)
- ; (lambda <id> <body>))
- (define-syntax mvlet
- (syntax-rules ()
- ((mvlet () body ...)
- (let () body ...))
- ((mvlet (clause ...) body ...)
- (mvlet-helper (clause ...) () (body ...)))))
- (define-syntax mvlet-helper
- (syntax-rules ()
- ((mvlet-helper () clauses (body ...))
- (let clauses body ...))
- ((mvlet-helper (((var . more-vars) val) more ...) clauses body)
- (copy-vars (var . more-vars) () val (more ...) clauses body))
- ((mvlet-helper ((var val) more ...) clauses body)
- (mvlet-helper (more ...) ((var val) . clauses) body))))
- (define-syntax copy-vars
- (syntax-rules ()
- ((copy-vars (var . more-vars) (copies ...)
- val more clauses body)
- (copy-vars more-vars (copies ... x)
- val more ((var x) . clauses) body))
- ((copy-vars () copies val more clauses body)
- (call-with-values
- (lambda () val)
- (lambda copies
- (mvlet-helper more clauses body))))
- ((copy-vars last (copies ...) val more clauses body)
- (call-with-values
- (lambda () val)
- (lambda (copies ... . lastx)
- (mvlet-helper more ((last lastx) . clauses) body))))))
- (define-syntax mvlet*
- (syntax-rules ()
- ((mvlet* () body ...)
- (let () body ...))
- ((mvlet* (((vars ...) val) clause ...) body ...)
- (call-with-values
- (lambda () val)
- (lambda (vars ...)
- (mvlet* (clause ...) body ...))))
- ((mvlet* ((var val) clause ...) body ...)
- (let ((var val)) (mvlet* (clause ...) body ...)))))
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