123 lines
3.4 KiB
Python
123 lines
3.4 KiB
Python
# -*- coding: utf-8 -*-
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#
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# Copyright © 2014, 2015, 2016, 2017 Simon Forman
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#
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# This file is part of Thun.
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#
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# Thun is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# Thun 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
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with Thun. If not see <http://www.gnu.org/licenses/>.
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#
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'''
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This module exports a single function for converting text to a joy
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expression as well as a single Symbol class and a single Exception type.
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The Symbol string class is used by the interpreter to recognize literals
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by the fact that they are not Symbol objects.
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A crude grammar::
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joy = term*
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term = int | float | string | '[' joy ']' | symbol
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A Joy expression is a sequence of zero or more terms. A term is a
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literal value (integer, float, string, or Joy expression) or a function
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symbol. Function symbols are unquoted strings and cannot contain square
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brackets. Terms must be separated by blanks, which can be omitted
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around square brackets.
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'''
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from re import Scanner
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from .utils.stack import list_to_stack
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BRACKETS = r'\[|\]'
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BLANKS = r'\s+'
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WORDS = r'[^[\]\s]+'
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token_scanner = Scanner([
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(BRACKETS, lambda _, token: token),
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(BLANKS, None),
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(WORDS, lambda _, token: token),
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])
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class Symbol(str):
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'''A string class that represents Joy function names.'''
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__repr__ = str.__str__
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def text_to_expression(text):
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'''Convert a string to a Joy expression.
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When supplied with a string this function returns a Python datastructure
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that represents the Joy datastructure described by the text expression.
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Any unbalanced square brackets will raise a ParseError.
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:param str text: Text to convert.
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:rtype: stack
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:raises ParseError: if the parse fails.
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'''
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return _parse(_tokenize(text))
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class ParseError(ValueError):
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'''Raised when there is a error while parsing text.'''
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def _tokenize(text):
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'''Convert a text into a stream of tokens.
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Converts function names to Symbols.
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Raise ParseError (with some of the failing text) if the scan fails.
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'''
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tokens, rest = token_scanner.scan(text)
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if rest:
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raise ParseError(
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'Scan failed at position %i, %r'
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% (len(text) - len(rest), rest[:10])
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)
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return tokens
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def _parse(tokens):
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'''
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Return a stack/list expression of the tokens.
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'''
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frame = []
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stack = []
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for tok in tokens:
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if tok == '[':
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stack.append(frame)
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frame = []
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elif tok == ']':
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v = frame
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try: frame = stack.pop()
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except IndexError:
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raise ParseError('Extra closing bracket.')
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frame.append(list_to_stack(v))
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elif tok == 'true':
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frame.append(True)
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elif tok == 'false':
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frame.append(False)
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else:
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try:
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thing = int(tok)
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except ValueError:
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thing = Symbol(tok)
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frame.append(thing)
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if stack:
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raise ParseError('Unclosed bracket.')
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return list_to_stack(frame)
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