impc:ti:variable-substitution-pairs   scheme

(define impc:ti:variable-substitution-pairs
  (lambda (t1 t2)
    (if (or (not (list? t1))
            (not (list? t2))
            (<> (length t1) (length t2)))
        '()
        (let ((pairs
               (flatten (map (lambda (a b)
                               (cond ((list? a)
                                      (impc:ti:variable-substitution-pairs a b))
                                     ((atom? a)
                                      (if (and (impc:ir:type? a)
                                               (symbol? b)
                                               (regex:match? (symbol->string b) "^!"))
                                          (cons (symbol->string b) (impc:ir:pretty-print-type a))))
                                     (else '())))
                             t1 t2))))
          pairs))))