Ambiguous grammar :
A sentence may correspond to a plurality of the syntax tree, a sentence may correspond to a plurality of the leftmost / rightmost derivation.
If a grammar of a sentence may correspond to two different syntax tree, called the grammar is ambiguous in.
Two different grammar may be the same language.
If all the grammar of a language is ambiguous, and claimed that this language inherent ambiguity.
Determine whether a grammar is ambiguous is recursively unsolvable.
2. Try to write grammar PL / 0 language.
Integer n n :: = 1 | 2 | ..... | 9 | 0
Identifier i i :: = <letters> | {<letters> | <number>}
Expression e :: = [+ | -] <item> {<subtraction operator> <term>}
Conditional statement :: = if <condition> then <statement>
Assignment :: = <id>: = <expression>
Compound statement :: = begin <statement> {; <statement>} end
Function :: = <Description Type> <function name> <compound statement>
Program :: = [<Constant Description section>] [<Variable Description section>] [<Process Description section>] <statement>