What do you mean by ambiguity in grammar in TOC?

A grammar is said to be ambiguous if there exists more than one left most derivation or more than one right most derivation or more than one parse tree for a given input string.

  • If the grammar is not ambiguous then we call it unambiguous grammar.
  • If the grammar has ambiguity then it is good for compiler construction.
  • No method can automatically detect and remove the ambiguity, but we can remove the ambiguity by re-writing the whole grammar without ambiguity.


Let us consider a grammar with production rules, as shown below −

E = I

E = E+E

E = E*E

E = (E)

E = ε|0|1|2|3...9

Let's consider a string "3*2+5"

If the above grammar generates two parse trees by using Left most derivation (LMD) then, we can say that the given grammar is ambiguous grammar.

Since there are two parse trees for a single string, then we can say the given grammar is ambiguous grammar.

Consider another example

Check whether the grammar is ambiguous or not.




For the string "a(a)(a)a" the above grammar can generate two parse trees, as given below −

Updated on: 12-Jun-2021

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