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;;; Copyright 2024 Masaya Tojo <masaya@tojo.tokyo>
;;;
;;; Licensed under the Apache License, Version 2.0 (the "License");
;;; you may not use this file except in compliance with the License.
;;; You may obtain a copy of the License at
;;;
;;; http://www.apache.org/licenses/LICENSE-2.0
;;;
;;; Unless required by applicable law or agreed to in writing, software
;;; distributed under the License is distributed on an "AS IS" BASIS,
;;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
;;; See the License for the specific language governing permissions and
;;; limitations under the License.
(define-library (qklib infix)
(export infix->prefix
prefix->infix
current-operator-rule-set)
(import (scheme base)
(scheme case-lambda)
(only (srfi 1) car+cdr fold break! reverse! append-map)
(only (srfi 26) cut cute)
(srfi 35)
(qklib infix rule-set))
(begin
(define (make-default-operator-rule-set)
(rule-set
(list
(operator '+ 1 'left (unit 0))
(operator '- 1 'left (unit 0 #t))
(operator '* 2 'left (unit 1))
(operator '/ 2 'left (unit 1 #t))
(operator '^ 3 'right #f (prefix 'expt)))))
(define current-operator-rule-set
(make-parameter (make-default-operator-rule-set)))
(define-condition-type &infix-error &error
infix-error?
(expr infix-error-expr))
(define (all-list-copy x)
(map-all-list list-copy x))
(define infix->prefix
(case-lambda
((expr failure)
(call/cc
(lambda (return)
(let ((rs (current-operator-rule-set)))
(map-all-list (cut infix->prefix-1 <> rs (lambda (e) (return (failure e))))
expr)))))
((expr)
(infix->prefix expr (lambda (e) #f)))))
(define (map-all-list f expr)
(f (map-cars f expr)))
(define (map-cars f expr)
(if (pair? expr)
(if (pair? (car expr))
(cons (f (map-cars f (car expr)))
(map-cars f (cdr expr)))
(cons (car expr)
(map-cars f (cdr expr))))
expr))
(define (infix->prefix-1 expr rs fail)
(define (not-single-error x)
(fail (make-compound-condition
(condition (&infix-error (expr x)))
(condition (&message (message "Invalid infix operator usage"))))))
(cond ((minimum-precedence expr rs)
=> (lambda (op)
(let ->prefix ((expr (list-copy expr))
(op op))
(define (make-prefix left op right)
(let ((left-op (minimum-precedence left rs))
(right-op (minimum-precedence right rs)))
(cond ((and (operator? left-op) (operator? right-op))
(list op
(->prefix left left-op)
(->prefix right right-op)))
((operator? left-op)
(if (single? right)
`(,op ,(->prefix left left-op) ,(car right))
(not-single-error (append left (cons op right)))))
((operator? right-op)
(if (single? left)
`(,op ,(car left) ,(->prefix right right-op))
(not-single-error (append left (cons op right)))))
(else
(if (and (single? left) (single? right))
`(,op ,(car left) ,(car right))
(not-single-error (append left (cons op right))))))))
(cond ((single? expr) (operator-symbol op))
((operator-left? op)
(let ((rev-expr (reverse! expr)))
(let-values (((rev-lst op+rev-rest) (break! (cute eqv? (operator-symbol op) <>) rev-expr)))
(let-values (((op rev-rest) (car+cdr op+rev-rest)))
(make-prefix (reverse! rev-rest) op (reverse! rev-lst))))))
(else
(let-values (((lst op+rest) (break! (cute eqv? (operator-symbol op) <>) expr)))
(let-values (((op rest) (car+cdr op+rest)))
(make-prefix lst op rest))))))))
(else expr)))
(define (prefix->infix expr)
(let ((rs (current-operator-rule-set)))
(let-values (((result _precedence) (%prefix->infix expr rs)))
result)))
(define (operator-inv? x)
(cond ((operator-unit x) => (cut unit-inv? <>))
(else #f)))
(define (%prefix->infix expr rs)
(let ->infix ((expr expr))
(define (->infix-fst expr)
(let-values (((x _) (->infix expr)))
x))
(if (not (pair? expr))
(values expr -inf.0)
(let-values (((op args) (car+cdr expr)))
(cond ((rule-set-prefix-ref rs op)
=> (lambda (op)
(let ((p (operator-precedence op))
(sym (operator-symbol op)))
(cond ((and (null? args)
(not (operator-inv? op))
(operator-unit op))
=> (lambda (u) (values (unit-value u) -inf.0)))
((single? args)
(let-values (((x xp) (->infix (car args))))
(cond ((operator-inv? op)
(values `(,(unit-value (operator-unit op))
,sym
,@(if (<= p xp) x (list x)))
p))
((operator-unit op)
(values x xp))
(else (values (list sym x) -inf.0)))))
((pair? args)
(values (cdr
(append-map (lambda (arg)
(let-values (((x xp) (->infix arg)))
(cons sym (if (<= p xp) x (list x)))))
args))
p))
(else (values (map ->infix-fst expr) -inf.0))))))
(else (values (map ->infix-fst expr) -inf.0)))))))
(define (single? x)
(and (pair? x)
(null? (cdr x))))
(define (minimum-precedence expr rs)
(let ((dummy (operator 'dummy +inf.0)))
(let ((result
(fold (lambda (x y-op)
(let ((x-op (rule-set-infix-ref rs x)))
(cond ((operator? x-op)
(if (<= (operator-precedence x-op) (operator-precedence y-op)) x-op y-op))
(else y-op))))
dummy
expr)))
(if (eq? dummy result)
#f
result))))
))
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