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Preserve minimum possible arity in case-lambda-generated procedure #1167

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b9fbb90
Preserve minimum possible arity in case-lambda
aartaka Aug 13, 2026
8a3faf1
Remove SRFI 16 dependence on SRFI 1
aartaka Aug 13, 2026
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73 changes: 55 additions & 18 deletions lib/srfi/16.sld
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Original file line number Diff line number Diff line change
Expand Up @@ -3,21 +3,58 @@
(export case-lambda)
(import (chibi))
(begin
(define-syntax %case
(syntax-rules ()
((%case args len n p ((params ...) . body) . rest)
(if (= len (length '(params ...)))
(apply (lambda (params ...) . body) args)
(%case args len 0 () . rest)))
((%case args len n (p ...) ((x . y) . body) . rest)
(%case args len (+ n 1) (p ... x) (y . body) . rest))
((%case args len n (p ...) (y . body) . rest)
(if (>= len n)
(apply (lambda (p ... . y) . body) args)
(%case args len 0 () . rest)))
((%case args len n p)
(error "case-lambda: no cases matched"))))
(define-syntax case-lambda
(syntax-rules ()
((case-lambda . clauses)
(lambda args (let ((len (length* args))) (%case args len 0 () . clauses))))))))
(define-syntax %case
(syntax-rules ()
((%case (args ... . rest-arg) len n p ((params ...) . body) . rest)
(if (= len (length '(params ...)))
(apply (lambda (params ...) . body) args ... rest-arg)
(%case (args ... . rest-arg) len 0 () . rest)))
((%case args len n (p ...) ((x . y) . body) . rest)
(%case args len (+ n 1) (p ... x) (y . body) . rest))
((%case (args ... . rest-arg) len n (p ...) (y . body) . rest)
(if (>= len n)
(apply (lambda (p ... . y) . body) args ... rest-arg)
(%case (args ... . rest-arg) len 0 () . rest)))
((%case args len n p)
(error "case-lambda: no cases matched"))))
(define-syntax %shortest-arglist
(syntax-rules ()
((%shortest-arglist (collected ...) (a as ...) () cases clauses ...)
(%collect-args (collected ...) cases clauses ...))
((%shortest-arglist (collected ...) () (b bs ...) cases clauses ...)
(%collect-args (collected ...) cases clauses ...))
((%shortest-arglist (collected ...) () () cases clauses ...)
(%collect-args (collected ...) cases clauses ...))
((%shortest-arglist (collected ...) (a as ...) (b bs ...) cases clauses ...)
(%shortest-arglist (collected ... a) (as ...) (bs ...) cases clauses ...))))
(define-syntax %collect-args
(syntax-rules ()
;; Generate the actual lambda with the right minimum arity
((%collect-args (shortest ...) (clauses ...))
(lambda (shortest ... . rest)
(let ((len (length `((unquote shortest) ... . (unquote rest)))))

@ashinn ashinn Aug 14, 2026

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Suggested change
(let ((len (length `((unquote shortest) ... . (unquote rest)))))
(let ((len (+ (length '(shortest ...)) (length rest))))

(%case (shortest ... . rest) len 0 () clauses ...))))
;; Generate a lambda with a single rest argument
((%collect-args rest-arg (clauses ...))
(lambda rest-arg
(let ((len (length rest-arg)))
(%case rest-arg len 0 () clauses ...))))
;; Regular args: find the shorter of saved and new args
((%collect-args (shortest ...) (cases ...) ((args ...) body ...) clauses ...)
(%shortest-arglist () (shortest ...) (args ...) (cases ... ((args ...) body ...)) clauses ...))
;; Dotted args: only consider pre-dot args
((%collect-args (shortest ...) (cases ...) ((args ... . rest) body ...) clauses ...)
(%shortest-arglist () (shortest ...) (args ...) (cases ... ((args ... . rest) body ...)) clauses ...))
;; Rest arg: nullify the arglist and terminate
((%collect-args (shortest ...) (cases ...) (rest-arg body ...) clauses ...)
(%collect-args () (cases ... (rest-arg body ...)) clauses ...))
;; Dotted initial arglist
((%collect-args (shortest ... . rest) (cases ...) (args body ...) clauses ...)
(%collect-args (shortest ...) (cases ...) (args body ...) clauses ...))
;; Rest initial arglist: nullify the arglist and terminate
((%collect-args rest (cases ...) (args body ...) clauses ...)
(%collect-args () (cases ...) (cases ... (args body ...) clauses ...)))))
(define-syntax case-lambda
(syntax-rules ()
((case-lambda (args body ...) clauses ...)
(%collect-args args () (args body ...) clauses ...))))))