module/language/tree-il/canonicalize.scm

   1 ;;; Tree-il canonicalizer
   2
   3 ;; Copyright (C) 2011, 2012 Free Software Foundation, Inc.
   4
   5 ;;;; This library is free software; you can redistribute it and/or
   6 ;;;; modify it under the terms of the GNU Lesser General Public
   7 ;;;; License as published by the Free Software Foundation; either
   8 ;;;; version 3 of the License, or (at your option) any later version.
   9 ;;;;
  10 ;;;; This library is distributed in the hope that it will be useful,
  11 ;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 ;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 ;;;; Lesser General Public License for more details.
  14 ;;;;
  15 ;;;; You should have received a copy of the GNU Lesser General Public
  16 ;;;; License along with this library; if not, write to the Free Software
  17 ;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  18
  19 ;;; Code:
  20
  21 (define-module (language tree-il canonicalize)
  22   #:use-module (language tree-il)
  23   #:use-module (ice-9 match)
  24   #:use-module (srfi srfi-1)
  25   #:export (canonicalize!))
  26
  27 (define (tree-il-any proc exp)
  28   (tree-il-fold (lambda (exp res)
  29                   (or res (proc exp)))
  30                 (lambda (exp res)
  31                   (or res (proc exp)))
  32                 (lambda (exp res) res)
  33                 #f exp))
  34
  35 (define (canonicalize! x)
  36   (post-order!
  37    (lambda (x)
  38      (match x
  39        (($ <let> src () () () body)
  40         body)
  41        (($ <letrec> src _ () () () body)
  42         body)
  43        (($ <fix> src () () () body)
  44         body)
  45        (($ <dynlet> src () () body)
  46         body)
  47        (($ <prompt> src tag body handler)
  48         (define (escape-only? handler)
  49           (match handler
  50             (($ <lambda-case> _ (_ . _) _ _ _ _ (cont . _) body #f)
  51              (not (tree-il-any (lambda (x)
  52                                  (and (lexical-ref? x)
  53                                       (eq? (lexical-ref-gensym x) cont)))
  54                                body)))
  55             (else #f)))
  56         (define (thunk-application? x)
  57           (match x
  58             (($ <call> _
  59                 ($ <lambda> _ _ ($ <lambda-case> _ () #f #f #f))
  60                 ()) #t)
  61             (_ #f)))
  62         (define (make-thunk-application body)
  63           (define thunk
  64             (make-lambda #f '()
  65                          (make-lambda-case #f '() #f #f #f '() '() body #f)))
  66           (make-call #f thunk '()))
  67
  68         ;; This code has a nasty job to do: to ensure that either the
  69         ;; handler is escape-only, or the body is the application of a
  70         ;; thunk.  Sad but true.
  71         (if (or (escape-only? handler)
  72                 (thunk-application? body))
  73             #f
  74             (make-prompt src tag (make-thunk-application body) handler)))
  75        (_ #f)))
  76    x))