pattern-match.lsp

;-*- Mode:     Lisp -*-
;;;; Author:   Paul Dietz
;;;; Created:  Sat Dec  4 18:59:27 2004
;;;; Contains: Macro for pattern matching on S-exprs

(in-package :cl-test)

(defmacro pmatch (pattern form)
  (cond
   ((consp pattern)
    (let ((pcar (car pattern))
          (pcdr (cdr pattern))
          (v (gensym)))
      (case pcar
        ((:or)
         `(let ((,v ,form)) (or ,@(mapcar (lambda (sub) `(pmatch ,sub ,v))
                                          pcdr))))
        ((:and)
         `(let ((,v ,form)) (and ,@(mapcar (lambda (sub) `(pmatch ,sub ,v))
                                           pcdr))))
        ((:not)
         (assert (eql (length pcdr) 1))
         `(not (pmatch ,(car pcdr) ,form)))
        (t
         `(let ((,v ,form))
            (and (pmatch ,pcar (car ,v))
                 (pmatch ,pcdr (cdr ,v))))))))
   ((eql pattern '_) t)
   ((null pattern)
    `(null ,form))
   ((symbolp pattern)
    `(eql (quote ,pattern) ,form))
   (t
    `(eql ,pattern ,form))))

(defmacro matchcase (form &body cases)
  (let* ((v (gensym))
         (cond-cases
          (mapcar
           #'(lambda (case)
               (assert (consp case))
               (let ((pattern (car case))
                     (body (cdr case)))
                 `((pmatch ,pattern ,v) ,@body)))
           cases)))
    `(let ((,v ,form))
       (cond ,@cond-cases))))

(defmacro matchcase* (form &body cases)
  (let* ((block-name (gensym "DONE"))
         (v (gensym)))
    `(block ,block-name
       (let ((,v ,form))
         (cond
          ,@(mapcar
             #'(lambda (case)
                 (assert (consp case))
                 (let ((pat (car case))
                       (forms (cdr case))
                       (fail-name (gensym "FAIL")))
                   `((block ,fail-name
                       (and (pmatch ,pat ,v)
                            (macrolet ((fail () '(return-from ,fail-name nil)))
                              (return-from ,block-name
                                (progn ,@forms))))))))
             cases))))))