The grammar class and related APIs

After you write your grammar either as a Python string or as a separate file the next step is to instantiate the grammar object that will be used to create the parser.

There are two factory methods defined on the Grammar class for creating the Grammar instance:

  • Grammar.from_string(grammar_string) - if your grammar is given as a Python string,
  • Grammar.from_file(file_path) - if the grammar is given as a separate file.

Both methods return initialized Grammar object that is passed as the first and the only mandatory parameter for the Parser/GLRParser constructor.

Grammar factory methods additional parameters

Both methods from_string and from_file accept additional optional parameters:

  • recognizers - a dict of custom recognizers. These recognizers are mandatory if a non-textual content is being parsed and the grammar terminals don't provide recognizers. See recognizers section for more information.

  • debug - set to True to put the grammar in debug/trace mode. False by default. See debugging section for more information.

  • debug_parse - set to True to debug/trace grammar file/string parsing. False by default.

  • debug_colors - set to True to enable terminal colors in debug/trace output. False by default.

  • re_flags - regex flags used for regex recognizers. See Python re module. By default flags is set to re.MULTILINE.

  • ignore_case - By default parsing is case sensitive. Set this param to True for case-insensitive parsing.

Grammar class

Attributes

  • terminals - a dict of terminals (instances of Terminal) keyed by fully qualified name;

  • nonterminals - a dict of non-terminal (instances of NonTerminal) keyed by fully qualified name;

  • start_symbol - a grammar symbol of the start/root rule. By default this is the first rule in the grammar;

  • productions - a list of productions (Production instances);

  • recognizers - a dict of user supplied recognizers keyed by the terminal rule name;

  • classes - a dict of Python classes dynamically created for rules using named matches keyed by the rule name.

Methods

  • print_debug() - prints detailed debug/trace info;

  • get_terminal(name) - gets the terminal by the given fully qualified name or None if not found;

  • get_nonterminal(name) - gets the non-terminal by the given fully qualified name or None if not found;

  • get_symbol(name) - gets either a terminal or non-terminal by the given fully qualified name or None if not found.

GrammarSymbol class

This is a base class for Terminal and NonTerminal.

Attributes

  • name - the name of the grammar symbol,

  • fqn (property) - fully qualified name of the symbol. Qualified by import module names.

  • location - an instance of parglare.common.Location. Gives information about location in the file (position and span).

  • action_name - the action name assigned for the symbol. This is given in the grammar using the @ syntax. If action name is not provided in the grammar symbol name is used.

  • action_fqn (property) - the fully qualiifed action name for the symbol. Qualified by the names of import modules.

  • action - resolved reference to the action function given by the user using actions parameter of the parser. Overrides grammar action if provided. If not given will be the same as grammar_action.

  • grammar_action - resolved reference to the action function specified in the grammar. Not used if action attribute is defined, i.e. action overrides grammar_action.

Terminal class

Attributes

  • prior (int) - a priority used in disambiguation,

  • recognizer (callable) - a callable in charge of recognition of this terminal in the input stream,

  • prefer (bool) - If True this recognizer/terminal is preferred in case of conflict where multiple recognizer match at the same place and implicit disambiguation doesn't resolve the conflict.

  • dynamic (bool) - True if disambiguation should be resolved dynamically.

NonTerminal class

Attributes

  • productions (list) - A list of alternative productions for this non-terminal symbol.

Production class

Attributes

  • symbol (GrammarSymbol) - LHS of the production,

  • rhs (ProductionRHS) - RHS of this production,

  • assignments (dict) - Assignment instances keyed by match name. Created by named matches,

  • assoc (int) - associativity of the production. See parglare.grammar.ASSOC_{NONE|LEFT|RIGHT}

  • prior (int) - integer defining priority of this production. Default priority is 10.

  • dynamic (bool) - True if this production disambiguation should be resolved dynamically.

  • prod_id (int) - ordinal number of the production in the grammar,

  • prod_symbol_id - zero-based ordinal of the production for the symbol grammar symbol, i.e. the ordinal for the alternative choice for this symbol.

ProductionRHS class

Represents right hand side of the production. Inherits list and keeps symbols from the production but doesn't count nor returns by index EMPTY symbols in the production.