Macros

gistfile1.scm

;; AST style:

    ((equal? term "cond")
     (define (transform i)
       (if (or (> i node.children.length)
               (eq? i node.children.length))
           null
           (let ((n (vector-ref node.children i)))
             (let ((condition (vector-ref n.children 0))
                   (res (ast.node ast.LIST
                                  null
                                  (vector-concat
                                   (list (ast.node ast.TERM (make-symbol "begin")))
                                   (n.children.slice 1)))))
               (if (and (eq? condition.type ast.TERM)
                        (equal? condition.data.str "else"))
                   res
                   (ast.add_child
                    (ast.node ast.LIST
                              null
                              (list (ast.node ast.TERM (make-symbol "if"))
                                    condition
                                    res))
                    (transform (+ i 1))))))))
     (let ((res (transform 1)))
       ;; maintain node links
       (set! res.link node.link)
       (parse res)))

;; define-macro style:

(define-macro (cond . forms)
  (if (null? forms)
      '#f
      (let ((form (car forms)))
        (if (eq? (car form) 'else)
            `(begin ,@(cdr form))
            `(if ,(car form)
                 (begin ,@(cdr form))
                 (cond ,@(cdr forms)))))))

;; syntax-parse style:
(define-syntax cond
  (syntax-parser
    [(cond) #'#f]
    [(cond [(~literal else) rest ...] more ....) #'(begin rest ...)]
    [(cond [tst rhs ...] more ...)
     #'(if tst (begin rhs ...) (cond more ...))]))