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New Features of Eli Version 4.7

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Abstract Rule Names in Mapping Rules

Some abstract grammars have several rules with different names and identical signatures (this is relatively common in computed trees, see Computed Subtrees of LIDO - Reference Manual). If such rules are represented in an unambiguous manner in text, and that text is parsed, one must be able to map the disambiguated concrete rules into the appropriate abstract rules. Because the abstract rules have identical signatures, pattern matching won't work.

In order to solve this problem, the Maptool now accepts an optional rule name in a rule mapping (see Specifying rule mappings of Syntactic Analysis). A simple example might be a representation of dyadic expressions without explicit operators:

RULE Add: Expression ::= Expression Expression END;
RULE Mul: Expression ::= Expression Expression END;
Suppose that such nodes are represented in text by fully-parenthesized arithmetic expressions in the standard notation. Rule mappings specifying the rule names explicitly would then be needed to disambiguate the pattern match:

Expression: '(' Expression '+' Expression ')' < $1 $2 >: Add .
Expression: '(' Expression '*' Expression ')' < $1 $2 >: Mul .

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