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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 #f #t))
(operator '- 1 'left (unit 0 #t #t))
(operator '* 2 'left (unit 1))
(operator '/ 2 'left (unit 1 #t))
(operator '^ 3 'right #f (prefix 'expt #t)))))
(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 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 (operator-unit-unary? op)
(cond ((operator-unit op) => unit-unary?)
(else #f)))
(define (infix->prefix-1 expr rs fail)
(cond ((and (pair? expr)
(single? (cdr expr))
(let ((op (rule-set-infix-ref rs (car expr))))
(if (and op (operator-unit-unary? op))
op
#f)))
=> (lambda (op)
(let ((arg (car (cdr expr)))
(unit (operator-unit op)))
(if (rule-set-infix-ref rs arg)
(fail expr)
(if (unit-inv? unit)
expr
arg)))))
((minimum-precedence expr rs)
=> (lambda (op)
(let ->prefix ((expr (list-copy expr))
(op op))
(define (make-prefix left op-sym right)
(define (->infix left op-sym right)
(append left (cons op-sym right)))
(let ((left-op (minimum-precedence left rs))
(right-op (minimum-precedence right rs)))
(cond ((and (operator? left-op) (operator? right-op))
(list op-sym
(->prefix left left-op)
(->prefix right right-op)))
((operator? left-op)
(if (single? right)
(list op-sym (->prefix left left-op) (car right))
(fail (->infix left op-sym right))))
((operator? right-op)
(if (single? left)
(list op-sym (car left) (->prefix right right-op))
(fail (->infix left op-sym right))))
(else
(if (and (single? left) (single? right))
(list op-sym (car left) (car right))
(fail (->infix left op-sym right)))))))
(if (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-sym rev-rest) (car+cdr op+rev-rest)))
(make-prefix (reverse! rev-rest) op-sym (reverse! rev-lst)))))
(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
(case-lambda
((expr failure)
(let ((rs (current-operator-rule-set)))
(call-with-current-continuation
(lambda (return)
(let-values (((result _precedence) (%prefix->infix expr rs (lambda (e) (return (failure e))))))
result)))))
((expr)
(prefix->infix expr (lambda (e) #f)))))
(define (operator-unit-inv? x)
(cond ((operator-unit x) => (cut unit-inv? <>))
(else #f)))
(define (%prefix->infix expr rs failure)
(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-prefix-sym args) (car+cdr expr)))
(cond ((rule-set-prefix-ref rs op-prefix-sym)
=> (lambda (op)
(let ((p (operator-precedence op))
(op-sym (operator-symbol op)))
(define (select x xp)
(if (<= p xp) x (list x)))
(cond ((null? args)
(cond ((and (not (operator-unit-inv? op))
(operator-unit op))
=> (lambda (u) (values (unit-value u) -inf.0)))
(else (failure expr))))
((null? (cdr args))
(let-values (((x xp) (->infix (car args))))
(cond ((operator-unit op)
=> (lambda (u)
(if (unit-inv? u)
(if (unit-unary? u)
(values `(,op-sym ,x) -inf.0)
(values `(,(unit-value (operator-unit op))
,op-sym
,@(select x xp))
p))
(values x xp))))
(else (failure expr)))))
((null? (cdr (cdr args)))
(let-values (((x xp) (->infix (car args)))
((y yp) (->infix (cadr args))))
(values `(,@(select x xp) ,op-sym ,@(select y yp)) p)))
(else
(if (and (operator-prefix op)
(prefix-fix? (operator-prefix op)))
(failure expr)
(values (cdr (append-map (lambda (arg)
(let-values (((x xp) (->infix arg)))
(cons op-sym (select x xp))))
args))
p)))))))
(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)
(cond ((rule-set-infix-ref rs x)
=> (lambda (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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