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#| syntax-funs.jl -- syntax expansion functions
$Id: syntax-funs.jl,v 1.8 2000/09/04 21:12:42 john Exp $
Copyright (C) 2000 John Harper <john@dcs.warwick.ac.uk>
This file is part of librep.
librep is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
librep is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with Jade; see the file COPYING. If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
|#
(define-structure scheme.syntax-funs
(export parse-define
expand-lambda
expand-if
expand-set!
expand-cond
expand-case
expand-and
expand-or
expand-let
expand-let*
expand-letrec
expand-do
expand-delay
expand-define)
(open rep)
;;; syntax
;; returns (VAR BODY) suitable for putting in a letrec
(define (parse-define form)
(let loop ((name (cadr form))
(body (caddr form)))
(if (symbolp name)
`(,name ,body)
(loop (car name) `(lambda ,(cdr name) ,body)))))
(define (expand-lambda vars . body)
(let (header)
(while (eq (caar body) 'define)
(setq header (cons (parse-define (car body)) header))
(setq body (cdr body)))
(if header
`(\#lambda ,vars (letrec ,(nreverse header) ,@body))
`(\#lambda ,vars ,@body))))
(define (expand-if test consequent . alternative)
(cond ((cdr alternative)
(error "Scheme `if' only takes one else form"))
(alternative
`(\#cond ((\#test ,test) ,consequent)
('t ,(car alternative))))
(t `(\#cond ((\#test ,test) ,consequent)))))
(define (expand-set! variable expression)
`(\#setq ,variable ,expression))
(define (expand-cond . args)
(let ((first (car args))
(rest (cdr args)))
(cond ((null args) '#f)
((eq (car first) 'else)
`(begin ,@(cdr first)))
((eq (cadr first) '=>)
(let ((tem (gensym)))
`(let ((,tem ,(car first)))
(if ,tem
(,(caddr first) ,tem)
,@(and rest `((cond ,@rest)))))))
(t `(if ,(car first)
(begin ,@(cdr first))
,@(and rest `((cond ,@rest))))))))
(define (expand-case key . clauses)
(let ((tem (gensym)))
(let loop ((body nil)
(rest clauses))
(if rest
(let ((this (car rest)))
(loop (cons (cond ((eq (car this) 'else) `(else ,@(cdr this)))
((cdar this)
`((memv ,tem ',(car this)) ,@(cdr this)))
(t `((eqv? ,tem ',(caar this)) ,@(cdr this))))
body)
(cdr rest)))
`(let ((,tem ,key))
(cond ,@(nreverse body)))))))
(define (expand-or . args)
(cond
((null args) '#f)
((null (cdr args)) (car args))
(t (let ((tem (gensym)))
`((lambda (,tem)
(if ,tem ,tem (or ,@(cdr args))))
,(car args))))))
(define (expand-and . args)
(cond
((null args) '#t)
((null (cdr args)) (car args))
(t `(cond (,(car args) (and ,@(cdr args))) (else #f)))))
(define (expand-let . args)
(let (fun vars values)
(when (and (car args) (symbolp (car args)))
;; named let
(setq fun (car args))
(setq args (cdr args)))
(setq vars (mapcar car (car args)))
(setq values (mapcar cadr (car args)))
(if fun
;; use the progn so the compiler notices the inner letrec
;; (else it will get macroexpanded away too soon)
`(begin (letrec
((,fun (lambda ,vars ,@(cdr args))))
(,fun ,@values)))
`((lambda ,vars ,@(cdr args)) ,@values))))
(define (expand-let* bindings . body)
(if (null bindings)
`((lambda () ,@body))
`((lambda (,(caar bindings))
(let* ,(cdr bindings) ,@body))
,(cadar bindings))))
(define (expand-letrec bindings . body)
(let ((vars (mapcar car bindings))
(setters (mapcar (lambda (x) `(set! ,@x)) bindings))
(initial (make-list (length bindings) ''())))
(let loop ((header '())
(body body))
(if (eq (caar body) 'define)
(loop (cons (parse-define (car body)) header) (cdr body))
(if header
`((lambda ,vars ,@setters
(letrec ,(nreverse header) ,@body)) ,@initial)
`((lambda ,vars ,@setters ,@body) ,@initial))))))
(define (expand-do vars test . body)
(let ((tem (gensym)))
`(let ,tem ,(mapcar (lambda (var)
(list (car var) (cadr var))) vars)
(if ,(car test)
(begin ,@(cdr test))
(begin
,@body
(,tem ,@(mapcar (lambda (var)
(if (cddr var)
(caddr var)
(car var))) vars)))))))
(define (expand-delay expression)
`(\#make-promise (lambda () ,expression)))
(define (expand-define . args)
(if (symbolp (car args))
(cons '\#define args)
`(define ,(caar args) (lambda ,(cdar args) ,@(cdr args))))))
|
