plet-make-bindings   scheme

;; @ignore
;; A helper method for the c{plet} macro. Given a list of pairs,
;; (pattern datum), plet-make-bindings transforms it into a pair
;; of "let" bindings s.t.:
;;  1. the car of the pair is a list of p:match invocations
;;     bound to named match results. For example:
;;     ((@mr0 (p:match '(?a . ?b) p1)) (@mr1 (p:match '(?c . ?d) p2)))
;;  2. the cdr is a list of pattern variable bindings, e.g.:
;;       ((a (match-result:get @mr0 'a))
;;        (b (match-result:get @mr0 'b))
;;        (c (match-result:get @mr1 'c))
;;        (d (match-result:get @mr1 'd)))
(define (plet-make-bindings pattern-pairs rename)
  (let lp
      ((i 0)
       (pattern-pairs pattern-pairs))
    (cond ((null? pattern-pairs) (cons () ()))
          (else
           (let* ((first-pair (first pattern-pairs))
                  (pattern    (car first-pair))
                  (datum      (cadr first-pair))
                  (compiled   (p:compile pattern))
                  (mr         (rename (string->symbol (string-append "@mr" (number->string i)))))
                  (vars       (matcher:variables compiled))
                  (bindings   (map (lambda (var)
                                     (list var `(match-result:get ,mr (quote ,var))))
                                   vars))
                  (next-bindings (lp (1+ i) (cdr pattern-pairs))))
             (cons (cons `(,mr (p:assert-match ,(list 'quasiquote pattern) ,datum))
                         (car next-bindings))
                   (append bindings (cdr next-bindings))))))))