"Parses and creates Grammar objects" import os.path import sys from ast import literal_eval from copy import deepcopy from .utils import bfs from .lexer import Token, TerminalDef, PatternStr, PatternRE from .parse_tree_builder import ParseTreeBuilder from .parser_frontends import LALR_TraditionalLexer from .common import LexerConf, ParserConf from .grammar import RuleOptions, Rule, Terminal, NonTerminal, Symbol from .utils import classify, suppress from .exceptions import GrammarError, UnexpectedCharacters, UnexpectedToken from .tree import Tree, SlottedTree as ST from .visitors import Transformer, Visitor, v_args, Transformer_InPlace inline_args = v_args(inline=True) __path__ = os.path.dirname(__file__) IMPORT_PATHS = [os.path.join(__path__, 'grammars')] EXT = '.lark' _RE_FLAGS = 'imslux' _TERMINAL_NAMES = { '.' : 'DOT', ',' : 'COMMA', ':' : 'COLON', ';' : 'SEMICOLON', '+' : 'PLUS', '-' : 'MINUS', '*' : 'STAR', '/' : 'SLASH', '\\' : 'BACKSLASH', '|' : 'VBAR', '?' : 'QMARK', '!' : 'BANG', '@' : 'AT', '#' : 'HASH', '$' : 'DOLLAR', '%' : 'PERCENT', '^' : 'CIRCUMFLEX', '&' : 'AMPERSAND', '_' : 'UNDERSCORE', '<' : 'LESSTHAN', '>' : 'MORETHAN', '=' : 'EQUAL', '"' : 'DBLQUOTE', '\'' : 'QUOTE', '`' : 'BACKQUOTE', '~' : 'TILDE', '(' : 'LPAR', ')' : 'RPAR', '{' : 'LBRACE', '}' : 'RBRACE', '[' : 'LSQB', ']' : 'RSQB', '\n' : 'NEWLINE', '\r\n' : 'CRLF', '\t' : 'TAB', ' ' : 'SPACE', } # Grammar Parser TERMINALS = { '_LPAR': r'\(', '_RPAR': r'\)', '_LBRA': r'\[', '_RBRA': r'\]', 'OP': '[+*][?]?|[?](?![a-z])', '_COLON': ':', '_COMMA': ',', '_OR': r'\|', '_DOT': r'\.', 'TILDE': '~', 'RULE': '!?[_?]?[a-z][_a-z0-9]*', 'TERMINAL': '_?[A-Z][_A-Z0-9]*', 'STRING': r'"(\\"|\\\\|[^"\n])*?"i?', 'REGEXP': r'/(?!/)(\\/|\\\\|[^/\n])*?/[%s]*' % _RE_FLAGS, '_NL': r'(\r?\n)+\s*', 'WS': r'[ \t]+', 'COMMENT': r'//[^\n]*', '_TO': '->', '_IGNORE': r'%ignore', '_DECLARE': r'%declare', '_IMPORT': r'%import', 'NUMBER': r'\d+', } RULES = { 'start': ['_list'], '_list': ['_item', '_list _item'], '_item': ['rule', 'term', 'statement', '_NL'], 'rule': ['RULE _COLON expansions _NL', 'RULE _DOT NUMBER _COLON expansions _NL'], 'expansions': ['alias', 'expansions _OR alias', 'expansions _NL _OR alias'], '?alias': ['expansion _TO RULE', 'expansion'], 'expansion': ['_expansion'], '_expansion': ['', '_expansion expr'], '?expr': ['atom', 'atom OP', 'atom TILDE NUMBER', 'atom TILDE NUMBER _DOT _DOT NUMBER', ], '?atom': ['_LPAR expansions _RPAR', 'maybe', 'value'], 'value': ['terminal', 'nonterminal', 'literal', 'range'], 'terminal': ['TERMINAL'], 'nonterminal': ['RULE'], '?name': ['RULE', 'TERMINAL'], 'maybe': ['_LBRA expansions _RBRA'], 'range': ['STRING _DOT _DOT STRING'], 'term': ['TERMINAL _COLON expansions _NL', 'TERMINAL _DOT NUMBER _COLON expansions _NL'], 'statement': ['ignore', 'import', 'declare'], 'ignore': ['_IGNORE expansions _NL'], 'declare': ['_DECLARE _declare_args _NL'], 'import': ['_IMPORT _import_path _NL', '_IMPORT _import_path _LPAR name_list _RPAR _NL', '_IMPORT _import_path _TO TERMINAL _NL'], '_import_path': ['import_lib', 'import_rel'], 'import_lib': ['_import_args'], 'import_rel': ['_DOT _import_args'], '_import_args': ['name', '_import_args _DOT name'], 'name_list': ['_name_list'], '_name_list': ['name', '_name_list _COMMA name'], '_declare_args': ['name', '_declare_args name'], 'literal': ['REGEXP', 'STRING'], } @inline_args class EBNF_to_BNF(Transformer_InPlace): def __init__(self): self.new_rules = [] self.rules_by_expr = {} self.prefix = 'anon' self.i = 0 self.rule_options = None def _add_recurse_rule(self, type_, expr): if expr in self.rules_by_expr: return self.rules_by_expr[expr] new_name = '__%s_%s_%d' % (self.prefix, type_, self.i) self.i += 1 t = NonTerminal(new_name) tree = ST('expansions', [ST('expansion', [expr]), ST('expansion', [t, expr])]) self.new_rules.append((new_name, tree, self.rule_options)) self.rules_by_expr[expr] = t return t def expr(self, rule, op, *args): if op.value == '?': return ST('expansions', [rule, ST('expansion', [])]) elif op.value == '+': # a : b c+ d # --> # a : b _c d # _c : _c c | c; return self._add_recurse_rule('plus', rule) elif op.value == '*': # a : b c* d # --> # a : b _c? d # _c : _c c | c; new_name = self._add_recurse_rule('star', rule) return ST('expansions', [new_name, ST('expansion', [])]) elif op.value == '~': if len(args) == 1: mn = mx = int(args[0]) else: mn, mx = map(int, args) if mx < mn: raise GrammarError("Bad Range for %s (%d..%d isn't allowed)" % (rule, mn, mx)) return ST('expansions', [ST('expansion', [rule] * n) for n in range(mn, mx+1)]) assert False, op class SimplifyRule_Visitor(Visitor): @staticmethod def _flatten(tree): while True: to_expand = [i for i, child in enumerate(tree.children) if isinstance(child, Tree) and child.data == tree.data] if not to_expand: break tree.expand_kids_by_index(*to_expand) def expansion(self, tree): # rules_list unpacking # a : b (c|d) e # --> # a : b c e | b d e # # In AST terms: # expansion(b, expansions(c, d), e) # --> # expansions( expansion(b, c, e), expansion(b, d, e) ) self._flatten(tree) for i, child in enumerate(tree.children): if isinstance(child, Tree) and child.data == 'expansions': tree.data = 'expansions' tree.children = [self.visit(ST('expansion', [option if i==j else other for j, other in enumerate(tree.children)])) for option in set(child.children)] self._flatten(tree) break def alias(self, tree): rule, alias_name = tree.children if rule.data == 'expansions': aliases = [] for child in tree.children[0].children: aliases.append(ST('alias', [child, alias_name])) tree.data = 'expansions' tree.children = aliases def expansions(self, tree): self._flatten(tree) tree.children = list(set(tree.children)) class RuleTreeToText(Transformer): def expansions(self, x): return x def expansion(self, symbols): return symbols, None def alias(self, x): (expansion, _alias), alias = x assert _alias is None, (alias, expansion, '-', _alias) # Double alias not allowed return expansion, alias.value @inline_args class CanonizeTree(Transformer_InPlace): def maybe(self, expr): return ST('expr', [expr, Token('OP', '?', -1)]) def tokenmods(self, *args): if len(args) == 1: return list(args) tokenmods, value = args return tokenmods + [value] class PrepareAnonTerminals(Transformer_InPlace): "Create a unique list of anonymous terminals. Attempt to give meaningful names to them when we add them" def __init__(self, terminals): self.terminals = terminals self.term_set = {td.name for td in self.terminals} self.term_reverse = {td.pattern: td for td in terminals} self.i = 0 @inline_args def pattern(self, p): value = p.value if p in self.term_reverse and p.flags != self.term_reverse[p].pattern.flags: raise GrammarError(u'Conflicting flags for the same terminal: %s' % p) term_name = None if isinstance(p, PatternStr): try: # If already defined, use the user-defined terminal name term_name = self.term_reverse[p].name except KeyError: # Try to assign an indicative anon-terminal name try: term_name = _TERMINAL_NAMES[value] except KeyError: if value.isalnum() and value[0].isalpha() and value.upper() not in self.term_set: with suppress(UnicodeEncodeError): value.upper().encode('ascii') # Make sure we don't have unicode in our terminal names term_name = value.upper() if term_name in self.term_set: term_name = None elif isinstance(p, PatternRE): if p in self.term_reverse: # Kind of a wierd placement.name term_name = self.term_reverse[p].name else: assert False, p if term_name is None: term_name = '__ANON_%d' % self.i self.i += 1 if term_name not in self.term_set: assert p not in self.term_reverse self.term_set.add(term_name) termdef = TerminalDef(term_name, p) self.term_reverse[p] = termdef self.terminals.append(termdef) return Terminal(term_name, filter_out=isinstance(p, PatternStr)) def _rfind(s, choices): return max(s.rfind(c) for c in choices) def _fix_escaping(s): w = '' i = iter(s) for n in i: w += n if n == '\\': n2 = next(i) if n2 == '\\': w += '\\\\' elif n2 not in 'unftr': w += '\\' w += n2 w = w.replace('\\"', '"').replace("'", "\\'") to_eval = "u'''%s'''" % w try: s = literal_eval(to_eval) except SyntaxError as e: raise ValueError(s, e) return s def _literal_to_pattern(literal): v = literal.value flag_start = _rfind(v, '/"')+1 assert flag_start > 0 flags = v[flag_start:] assert all(f in _RE_FLAGS for f in flags), flags v = v[:flag_start] assert v[0] == v[-1] and v[0] in '"/' x = v[1:-1] s = _fix_escaping(x) if literal.type == 'STRING': s = s.replace('\\\\', '\\') return { 'STRING': PatternStr, 'REGEXP': PatternRE }[literal.type](s, flags) @inline_args class PrepareLiterals(Transformer_InPlace): def literal(self, literal): return ST('pattern', [_literal_to_pattern(literal)]) def range(self, start, end): assert start.type == end.type == 'STRING' start = start.value[1:-1] end = end.value[1:-1] assert len(start) == len(end) == 1, (start, end, len(start), len(end)) regexp = '[%s-%s]' % (start, end) return ST('pattern', [PatternRE(regexp)]) class TerminalTreeToPattern(Transformer): def pattern(self, ps): p ,= ps return p def expansion(self, items): assert items if len(items) == 1: return items[0] if len({i.flags for i in items}) > 1: raise GrammarError("Lark doesn't support joining terminals with conflicting flags!") return PatternRE(''.join(i.to_regexp() for i in items), items[0].flags if items else ()) def expansions(self, exps): if len(exps) == 1: return exps[0] if len({i.flags for i in exps}) > 1: raise GrammarError("Lark doesn't support joining terminals with conflicting flags!") return PatternRE('(?:%s)' % ('|'.join(i.to_regexp() for i in exps)), exps[0].flags) def expr(self, args): inner, op = args[:2] if op == '~': if len(args) == 3: op = "{%d}" % int(args[2]) else: mn, mx = map(int, args[2:]) if mx < mn: raise GrammarError("Bad Range for %s (%d..%d isn't allowed)" % (inner, mn, mx)) op = "{%d,%d}" % (mn, mx) else: assert len(args) == 2 return PatternRE('(?:%s)%s' % (inner.to_regexp(), op), inner.flags) def alias(self, t): raise GrammarError("Aliasing not allowed in terminals (You used -> in the wrong place)") def value(self, v): return v[0] class PrepareSymbols(Transformer_InPlace): def value(self, v): v ,= v if isinstance(v, Tree): return v elif v.type == 'RULE': return NonTerminal(v.value) elif v.type == 'TERMINAL': return Terminal(v.value, filter_out=v.startswith('_')) assert False def _choice_of_rules(rules): return ST('expansions', [ST('expansion', [Token('RULE', name)]) for name in rules]) class Grammar: def __init__(self, rule_defs, term_defs, ignore): self.term_defs = term_defs self.rule_defs = rule_defs self.ignore = ignore def compile(self): # We change the trees in-place (to support huge grammars) # So deepcopy allows calling compile more than once. term_defs = deepcopy(list(self.term_defs)) rule_defs = deepcopy(self.rule_defs) # =================== # Compile Terminals # =================== # Convert terminal-trees to strings/regexps transformer = PrepareLiterals() * TerminalTreeToPattern() for name, (term_tree, priority) in term_defs: if term_tree is None: # Terminal added through %declare continue expansions = list(term_tree.find_data('expansion')) if len(expansions) == 1 and not expansions[0].children: raise GrammarError("Terminals cannot be empty (%s)" % name) terminals = [TerminalDef(name, transformer.transform(term_tree), priority) for name, (term_tree, priority) in term_defs if term_tree] # ================= # Compile Rules # ================= # 1. Pre-process terminals transformer = PrepareLiterals() * PrepareSymbols() * PrepareAnonTerminals(terminals) # Adds to terminals # 2. Convert EBNF to BNF (and apply step 1) ebnf_to_bnf = EBNF_to_BNF() rules = [] for name, rule_tree, options in rule_defs: ebnf_to_bnf.rule_options = RuleOptions(keep_all_tokens=True) if options and options.keep_all_tokens else None tree = transformer.transform(rule_tree) rules.append((name, ebnf_to_bnf.transform(tree), options)) rules += ebnf_to_bnf.new_rules assert len(rules) == len({name for name, _t, _o in rules}), "Whoops, name collision" # 3. Compile tree to Rule objects rule_tree_to_text = RuleTreeToText() simplify_rule = SimplifyRule_Visitor() compiled_rules = [] for name, tree, options in rules: simplify_rule.visit(tree) expansions = rule_tree_to_text.transform(tree) for expansion, alias in expansions: if alias and name.startswith('_'): raise GrammarError("Rule %s is marked for expansion (it starts with an underscore) and isn't allowed to have aliases (alias=%s)" % (name, alias)) assert all(isinstance(x, Symbol) for x in expansion), expansion rule = Rule(NonTerminal(name), expansion, alias, options) compiled_rules.append(rule) return terminals, compiled_rules, self.ignore _imported_grammars = {} def import_grammar(grammar_path, base_paths=[]): if grammar_path not in _imported_grammars: import_paths = base_paths + IMPORT_PATHS for import_path in import_paths: with suppress(IOError): with open(os.path.join(import_path, grammar_path)) as f: text = f.read() grammar = load_grammar(text, grammar_path) _imported_grammars[grammar_path] = grammar break else: open(grammar_path) assert False return _imported_grammars[grammar_path] def import_from_grammar_into_namespace(grammar, namespace, aliases): imported_terms = dict(grammar.term_defs) imported_rules = {n:(n,t,o) for n,t,o in grammar.rule_defs} term_defs = [] rule_defs = [] def rule_dependencies(symbol): if symbol.type != 'RULE': return [] _, tree, _ = imported_rules[symbol] return tree.scan_values(lambda x: x.type in ('RULE', 'TERMINAL')) def get_namespace_name(name): try: return aliases[name].value except KeyError: return '%s.%s' % (namespace, name) to_import = list(bfs(aliases, rule_dependencies)) for symbol in to_import: if symbol.type == 'TERMINAL': term_defs.append([get_namespace_name(symbol), imported_terms[symbol]]) else: assert symbol.type == 'RULE' rule = imported_rules[symbol] for t in rule[1].iter_subtrees(): for i, c in enumerate(t.children): if isinstance(c, Token) and c.type in ('RULE', 'TERMINAL'): t.children[i] = Token(c.type, get_namespace_name(c)) rule_defs.append((get_namespace_name(symbol), rule[1], rule[2])) return term_defs, rule_defs def resolve_term_references(term_defs): # TODO Cycles detection # TODO Solve with transitive closure (maybe) token_dict = {k:t for k, (t,_p) in term_defs} assert len(token_dict) == len(term_defs), "Same name defined twice?" while True: changed = False for name, (token_tree, _p) in term_defs: if token_tree is None: # Terminal added through %declare continue for exp in token_tree.find_data('value'): item ,= exp.children if isinstance(item, Token): if item.type == 'RULE': raise GrammarError("Rules aren't allowed inside terminals (%s in %s)" % (item, name)) if item.type == 'TERMINAL': exp.children[0] = token_dict[item] changed = True if not changed: break def options_from_rule(name, *x): if len(x) > 1: priority, expansions = x priority = int(priority) else: expansions ,= x priority = None keep_all_tokens = name.startswith('!') name = name.lstrip('!') expand1 = name.startswith('?') name = name.lstrip('?') return name, expansions, RuleOptions(keep_all_tokens, expand1, priority=priority) def symbols_from_strcase(expansion): return [Terminal(x, filter_out=x.startswith('_')) if x.isupper() else NonTerminal(x) for x in expansion] @inline_args class PrepareGrammar(Transformer_InPlace): def terminal(self, name): return name def nonterminal(self, name): return name class GrammarLoader: def __init__(self): terminals = [TerminalDef(name, PatternRE(value)) for name, value in TERMINALS.items()] rules = [options_from_rule(name, x) for name, x in RULES.items()] rules = [Rule(NonTerminal(r), symbols_from_strcase(x.split()), None, o) for r, xs, o in rules for x in xs] callback = ParseTreeBuilder(rules, ST).create_callback() lexer_conf = LexerConf(terminals, ['WS', 'COMMENT']) parser_conf = ParserConf(rules, callback, 'start') self.parser = LALR_TraditionalLexer(lexer_conf, parser_conf) self.canonize_tree = CanonizeTree() def load_grammar(self, grammar_text, grammar_name=''): "Parse grammar_text, verify, and create Grammar object. Display nice messages on error." try: tree = self.canonize_tree.transform( self.parser.parse(grammar_text+'\n') ) except UnexpectedCharacters as e: context = e.get_context(grammar_text) raise GrammarError("Unexpected input at line %d column %d in %s: \n\n%s" % (e.line, e.column, grammar_name, context)) except UnexpectedToken as e: context = e.get_context(grammar_text) error = e.match_examples(self.parser.parse, { 'Unclosed parenthesis': ['a: (\n'], 'Umatched closing parenthesis': ['a: )\n', 'a: [)\n', 'a: (]\n'], 'Expecting rule or terminal definition (missing colon)': ['a\n', 'a->\n', 'A->\n', 'a A\n'], 'Alias expects lowercase name': ['a: -> "a"\n'], 'Unexpected colon': ['a::\n', 'a: b:\n', 'a: B:\n', 'a: "a":\n'], 'Misplaced operator': ['a: b??', 'a: b(?)', 'a:+\n', 'a:?\n', 'a:*\n', 'a:|*\n'], 'Expecting option ("|") or a new rule or terminal definition': ['a:a\n()\n'], '%import expects a name': ['%import "a"\n'], '%ignore expects a value': ['%ignore %import\n'], }) if error: raise GrammarError("%s at line %s column %s\n\n%s" % (error, e.line, e.column, context)) elif 'STRING' in e.expected: raise GrammarError("Expecting a value at line %s column %s\n\n%s" % (e.line, e.column, context)) raise tree = PrepareGrammar().transform(tree) # Extract grammar items defs = classify(tree.children, lambda c: c.data, lambda c: c.children) term_defs = defs.pop('term', []) rule_defs = defs.pop('rule', []) statements = defs.pop('statement', []) assert not defs term_defs = [td if len(td)==3 else (td[0], 1, td[1]) for td in term_defs] term_defs = [(name.value, (t, int(p))) for name, p, t in term_defs] rule_defs = [options_from_rule(*x) for x in rule_defs] # Execute statements ignore = [] for (stmt,) in statements: if stmt.data == 'ignore': t ,= stmt.children ignore.append(t) elif stmt.data == 'import': if len(stmt.children) > 1: path_node, arg1 = stmt.children else: path_node ,= stmt.children arg1 = None if isinstance(arg1, Tree): # Multi import dotted_path = path_node.children names = arg1.children aliases = names # Can't have aliased multi import, so all aliases will be the same as names else: # Single import dotted_path = path_node.children[:-1] names = [path_node.children[-1]] # Get name from dotted path aliases = [arg1] if arg1 else names # Aliases if exist grammar_path = os.path.join(*dotted_path) + EXT if path_node.data == 'import_lib': # Import from library g = import_grammar(grammar_path) else: # Relative import if grammar_name == '': # Import relative to script file path if grammar is coded in script base_file = os.path.abspath(sys.modules['__main__'].__file__) else: base_file = grammar_name # Import relative to grammar file path if external grammar file base_path = os.path.split(base_file)[0] g = import_grammar(grammar_path, base_paths=[base_path]) aliases_dict = dict(zip(names, aliases)) new_td, new_rd = import_from_grammar_into_namespace(g, '.'.join(dotted_path), aliases_dict) term_defs += new_td rule_defs += new_rd elif stmt.data == 'declare': for t in stmt.children: term_defs.append([t.value, (None, None)]) else: assert False, stmt # Verify correctness 1 for name, _ in term_defs: if name.startswith('__'): raise GrammarError('Names starting with double-underscore are reserved (Error at %s)' % name) # Handle ignore tokens # XXX A slightly hacky solution. Recognition of %ignore TERMINAL as separate comes from the lexer's # inability to handle duplicate terminals (two names, one value) ignore_names = [] for t in ignore: if t.data=='expansions' and len(t.children) == 1: t2 ,= t.children if t2.data=='expansion' and len(t2.children) == 1: item ,= t2.children if item.data == 'value': item ,= item.children if isinstance(item, Token) and item.type == 'TERMINAL': ignore_names.append(item.value) continue name = '__IGNORE_%d'% len(ignore_names) ignore_names.append(name) term_defs.append((name, (t, 0))) # Verify correctness 2 terminal_names = set() for name, _ in term_defs: if name in terminal_names: raise GrammarError("Terminal '%s' defined more than once" % name) terminal_names.add(name) if set(ignore_names) > terminal_names: raise GrammarError("Terminals %s were marked to ignore but were not defined!" % (set(ignore_names) - terminal_names)) resolve_term_references(term_defs) rules = rule_defs rule_names = set() for name, _x, _o in rules: if name.startswith('__'): raise GrammarError('Names starting with double-underscore are reserved (Error at %s)' % name) if name in rule_names: raise GrammarError("Rule '%s' defined more than once" % name) rule_names.add(name) for name, expansions, _o in rules: used_symbols = {t for x in expansions.find_data('expansion') for t in x.scan_values(lambda t: t.type in ('RULE', 'TERMINAL'))} for sym in used_symbols: if sym.type == 'TERMINAL': if sym not in terminal_names: raise GrammarError("Token '%s' used but not defined (in rule %s)" % (sym, name)) else: if sym not in rule_names: raise GrammarError("Rule '%s' used but not defined (in rule %s)" % (sym, name)) # TODO don't include unused terminals, they can only cause trouble! return Grammar(rules, term_defs, ignore_names) load_grammar = GrammarLoader().load_grammar