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ParserMonad.el
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ParserMonad.el
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;; -*- lexical-binding: t; -*-
;;; ParserMonad.el --- Parser monad that parses Lisp lists
;; Copyright (C) 2021 Ernests Kuznecovs
;; Author: Ernests Kuznecovs <ernestkuznecovs@gmail.com>
;; Keywords: extensions
;; This program 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 3 of the License, or
;; (at your option) any later version.
;; This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
(require 'monad)
;; (use-package monad
;; :straight
;; (monad
;; :type git
;; :host github
;; :repo "ernestkz/monad.el"))
(require 'cl-lib)
;; The type { a, b } denotes that the function accepts two arguments of type a and b
;; Parser :: { LispList -> Maybe (a . LispList) } -> Parser a
(defun Parser (f) (cons 'Parser f))
;; Parser-zero :: Parser a
(setq Parser-zero (Parser (lambda (_) Nothing)))
;; item :: Parser a
(setq Parser-item (Parser (lambda (inp) (if inp (Just (cons (car inp) (cdr inp))) Nothing))))
;; Parser-run :: { Parser a, LispList } -> Maybe (a . LispList)
(defun Parser-run (parser inp) (funcall (cdr parser) inp))
;; Parser-return :: { a } -> Parser a
(defun Parser-return (v) (Parser (lambda (inp) (Just (cons v inp)))))
;; Parser-fmap :: (a -> b) -> Parser a -> Parser b
(defun Parser-fmap (f p) (Parser-bind p (lambda (a) (Parser-return (funcall f a)))))
;; Parser-bind :: { Parser a, (a -> Parser b) } -> Parser b
(defun Parser-bind (p f)
(Parser (lambda (inp) (pcase (Parser-run p inp)
(`(Just . ,pair) (Parser-run (funcall f (car pair)) (cdr pair)))
(_ (Parser-run Parser-zero inp))))))
;; Parser-blind :: { Parser a, Parser b } -> Parser b
(defun Parser-blind (p1 p2) (Parser-bind p1 (lambda (_) p2)))
;; Parser-sat :: { a -> Bool } -> Parser a
(defun Parser-sat (p)
(monad-do Parser
(x Parser-item)
((guard (funcall p x)))
(return x)))
;; Parser-plus :: { Parser a, Parser a } -> Parser a
(defun Parser-plus (p1 p2) (Parser (lambda (inp) (Maybe-plus (Parser-run p1 inp) (Parser-run p2 inp)))))
;; Parser-plus-n :: { List Parser a } -> Parser a
(defun Parser-plus-n (&rest ps) (cl-reduce 'Parser-plus ps))
;; Parser-equal :: { LispItem } -> Parser LispItem
(defun Parser-equal (item) (Parser-sat (lambda (x) (equal item x))))
;; Parser-list :: { LispList } -> Parser LispList
(defun Parser-list-equal (list)
(if list
(monad-do Parser
(x (Parser-equal (car list)))
(xs (Parser-list-equal (cdr list)))
(return (cons x xs)))
(Parser-return nil)))
;; Parser-many :: { Parser a } -> Parser [a]
(defun Parser-many (p)
(Parser-plus
(monad-do Parser
(x p)
(xs (Parser-many p))
(return (cons x xs)))
(Parser-return nil)))
(defun Parser-oneornone (p) (Parser-plus p (Parser-return nil)))
;; Parser-many :: { Parser a } -> Parser [a]
(defun Parser-many1 (p)
(monad-do Parser
(x p)
(xs (Parser-many p))
(return (cons x xs))))
;; Parser-sepby :: { Parser a, Parser b } -> Parser [a]
(defun Parser-sepby (p sep)
(Parser-plus (Parser-sepby1 p sep) (Parser-return nil)))
;; Parser-sepby1 :: { Parser a, Parser b } -> Parser [a]
(defun Parser-sepby1 (p sep)
(monad-do Parser
(x p)
(xs (Parser-many (Parser-blind sep p)))
(return (cons x xs))))
;; Parser-bracket :: { Parser a, Parser b, Parser c } -> Parser b
(defun Parser-bracket (open p close)
(monad-do Parser
(open)
(x p)
(close)
(return x)))
;; Parser-symbol :: Parser Symbol
(setq Parser-symbol (Parser-sat 'symbolp))
;; Parser-list :: Parser LispList
(setq Parser-list (Parser-sat 'listp))
;; Parser-number :: Parser Number
(setq Parser-number (Parser-sat 'numberp))
;; Parser-string :: Parser String
(setq Parser-string (Parser-sat 'stringp))
(setq Parser-quoted-symbol (Parser-sat (lambda (x) (and
(listp x)
(eq 'quote (car x))
(symbolp (cadr x))
(null (cddr x))))))
(setq Parser-quoted-symbol-unwrap (Parser-fmap
(lambda (x) (cadr x))
Parser-quoted-symbol))
(setq Parser-unquoted-list (Parser-sat (lambda (x) (and
(listp x)
(not (eq 'quote (car x)))))))
(setq Parser-quoted-list (Parser-sat (lambda (x) (and
(listp x)
(eq 'quote (car x))
(listp (cadr x))
(null (cddr x))))))
(setq Parser-quoted-list-unwrap (Parser-fmap
(lambda (x) (cadr x))
Parser-quoted-list))
;; Runs p on the next item (a list), returns result, throws away the rest that's left in the list.
;; Fails the whole parse if fails.
;; Parser-nest :: { Parser a } -> Parser a
(defun Parser-nest (p) (monad-do Parser
(x Parser-list)
(pcase (Parser-run p x)
(`(Just . ,pair) (Parser-return (car pair)))
(_ Parser-zero))))
;; Maybe-plus :: { Maybe a, Maybe a } -> Maybe a
(defun Maybe-plus (m1 m2)
(pcase (list m1 m2)
(`((Just . ,x) ,_) m1)
(`(Nothing ,x) m2)))
(provide 'ParserMonad)
;;; ParserMonad.el ends here