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542aa859de
* module/language/tree-il/canonicalize.scm (canonicalize!): Fix a bug in which the sense of `escape-only?' was reversed. We never saw this though, because for other reasons, no prompts were being identified as escape-only.
86 lines
3.1 KiB
Scheme
86 lines
3.1 KiB
Scheme
;;; Tree-il canonicalizer
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;; Copyright (C) 2011, 2012 Free Software Foundation, Inc.
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;;;; This library is free software; you can redistribute it and/or
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;;;; modify it under the terms of the GNU Lesser General Public
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;;;; License as published by the Free Software Foundation; either
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;;;; version 3 of the License, or (at your option) any later version.
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;;;;
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;;;; This library is distributed in the hope that it will be useful,
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;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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;;;; Lesser General Public License for more details.
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;;;;
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;;;; You should have received a copy of the GNU Lesser General Public
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;;;; License along with this library; if not, write to the Free Software
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;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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;;; Code:
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(define-module (language tree-il canonicalize)
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#:use-module (language tree-il)
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#:use-module (ice-9 match)
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#:use-module (srfi srfi-1)
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#:export (canonicalize!))
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(define (tree-il-any proc exp)
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(tree-il-fold (lambda (exp res)
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(or res (proc exp)))
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(lambda (exp res)
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(or res (proc exp)))
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(lambda (exp res) res)
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#f exp))
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(define (canonicalize! x)
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(post-order!
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(lambda (x)
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(match x
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(($ <sequence> src (tail))
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tail)
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(($ <sequence> src exps)
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(and (any sequence? exps)
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(make-sequence src
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(append-map (lambda (x)
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(if (sequence? x)
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(sequence-exps x)
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(list x)))
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exps))))
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(($ <let> src () () () body)
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body)
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(($ <letrec> src _ () () () body)
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body)
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(($ <fix> src () () () body)
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body)
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(($ <dynlet> src () () body)
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body)
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(($ <prompt> src tag body handler)
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(define (escape-only? handler)
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(match handler
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(($ <lambda-case> _ (_ . _) _ _ _ _ (cont . _) body #f)
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(not (tree-il-any (lambda (x)
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(and (lexical-ref? x)
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(eq? (lexical-ref-gensym x) cont)))
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body)))
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(else #f)))
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(define (thunk-application? x)
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(match x
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(($ <application> _
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($ <lambda> _ _ ($ <lambda-case> _ () #f #f #f))
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()) #t)
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(_ #f)))
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(define (make-thunk-application body)
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(define thunk
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(make-lambda #f '()
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(make-lambda-case #f '() #f #f #f '() '() body #f)))
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(make-application #f thunk '()))
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;; This code has a nasty job to do: to ensure that either the
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;; handler is escape-only, or the body is the application of a
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;; thunk. Sad but true.
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(if (or (escape-only? handler)
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(thunk-application? body))
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#f
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(make-prompt src tag (make-thunk-application body) handler)))
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(_ #f)))
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x))
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