Parser parameters¶

There are several parameters you can pass during the parser construction. The mandatory first parameter is the Grammar instance. Other parameters are explained in the rest of this section.

All parameters described here work for both parglare.Parser and parglare.GLRParser classes.

actions¶

This parameters is a dict of actions keyed by the name of the grammar rule.

layout_actions¶

This parameter is used to specify actions called when the rules of layout sub-grammar are reduced. This is rarely needed but there are times when you would like to process matched layout (e.g. whitespaces, comments).

It is given in the same format as actions parameter, a dict of callables keyed by grammar rule names.

ws¶

This parameter specifies a string whose characters are considered to be whitespace. By default its value is '\n\r\t '. It is used if layout sub-grammar (LAYOUT grammar rule) is not defined. If LAYOUT rule is given in the grammar it is used instead and this parameter is ignored.

build_tree¶

A boolean whose default value is False. If set to True parser will call actions that will build the parse tree.

call_actions_during_tree_build¶

By default, this parameter is set to False. If set to True, parser will call actions during the parse tree parse tree building process. The return value of each action will be discarded, since they directly affect the parse tree building process.

prefer_shifts¶

By default set to True for LR parser and to False for GLR parser. In case of shift/reduce conflicts this strategy would favor shift over reduce. You can still use associativity rules to decide per production.

You can disable this rule on per-production basis by using nops on the production.

prefer_shifts_over_empty¶

By default set to True for LR parser and to False for GLR parser. In case of shift/reduce conflicts on empty reductions this strategy would favor shift over reduce. You can still use associativity rules to decide per production.

You can disable this rule on per-production basis by using nopse on the production.

error_recovery¶

By default set to False. If set to True default error recovery will be used. If set to a Python function, the function will be called to recover from errors. For more information see Error recovery.

start_production¶

By default the first rule of the grammar is the start rule. If you want to change this default behavior — for example you want to create multiple parsers from the same grammar with different start production — you can use this parameter. The parameter accepts the id of the grammar production. To get the id from the rule name use the get_production_id(rule_name) method of the grammar.

debug/debug_layout¶

This parameter if set to True will put the parser in debug mode. In this mode parser will print a detailed information of its actions to the standard output. To put layout subparser in the debug mode use the debug_layout parameter. Both parameters are set to False by default.

For more information see Debugging

debug_colors¶

Set this to True to enable terminal colors in debug/trace output. False by default.

tables¶

The value of this parameter is either parglare.LALR or parglare.SLR and it is used to chose the type of LR tables to create. By default LALR tables are used with a slight twist to avoid Reduce/Reduce conflicts that may happen with pure LALR tables. This parameter should not be used in normal circumstances but is provided more for experimentation purposes.

parse and parse_file calls¶

parse call is used to parse input string or list of objects. For parsing of textual file parse_file is used.

These two calls accepts the following parameters:

• input_str - first positional and mandatory parameter only for parse call - the input string/list of objects.

• position - the start position to parse from. By default 0.

• context - the context object to use. By default None - context object is created by the parser.

• file_name - first positional and mandatory parameter only for parse_file call - the name/path of the file to parse.

Token¶

This class from parglare.parser is used to represent lookahead tokens. Token is a concrete matched terminal from the input stream.

Attributes¶

• symbol (Terminal) - terminal grammar symbol represented by this token,

• value (list or str) - matched part of input stream,

• length (int) - length of matched input.