JLALR CFG File Format (.cfg)

A .cfg file is a text file representing a context-free grammar. The grammar must be augmented in the following sense: there must be exactly one production rule expanding the start symbol, and the right-hand-side of the rule must contain three symbols: a beginning-of-input terminal symbol followed by a non-terminal symbol followed by an end-of-input terminal symbol. The beginning-of-input and end-of-input terminal symbols must not appear in any other rule.

Context-free Grammar Representation

The context-free grammar representation has four components, in order:

• t, a positive integer giving the number of terminal symbols in the grammar, followed by t lines, each containing the name of a distinct terminal symbol. Each terminal symbol may be any string of one or more printable ascii characters, excluding white space.
• n, a positive integer giving the number of nonterminal symbols in the grammar, followed by n lines, each containing the name of a distinct nonterminal symbol. Each nonterminal symbol may be any string of one or more printable ascii characters, and must not be the same as any terminal symbol.
• A single line giving the name of the start symbol, which must be one of the nonterminal symbols
• r, a positive integer giving the number of production rules in the grammar, followed by r lines, each denoting a rule consisting of:
  • The left-hand-side (LHS) of the rule; a nonterminal symbol
  • The right-hand-side (RHS) of the rule; zero or more terminal or nonterminal symbols separated from each other, and from the LHS by a single space

Example .cfg file

sample.cfg

6
BOF
EOF
id
-
(
)
3
S
expr
term
S
5
S BOF expr EOF
expr term
expr expr - term
term id
term ( expr )