Ambiguous Grammars §

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• An ambiguous grammar permits more than one parse tree for some sentences. For example, parsing xxx with the following grammar:

S $\to$ AA

A $\to$ x | xx

• But useful:

expression $\to$ expression binop expression | integer

binop $\to$ + | - | * | /

• Use rules (e.g. BODMAS) to disambiguate, and/or rewrite:

expression $\to$ expression termop term | term

termop $\to$ + | -

term $\to$ term factorop integer | integer

factorop $\to$ * | /

See Also §

• Formal Languages