Simple look-ahead production

Examples > Java > Simple look-ahead production

The Java parser isn't LL (1) conform. The decision on the alternative to be chosen depends on a look-ahead of more than a single token. The IF and the WHILE construct of the TextTransformer allows such a foresight if in the respective condition a production is invoked for the look-ahead.

For example, if an identifier is recognized as next token in the statement production, then it isn't clear at first whether this identifier represents a label or an expression. It represents a label if a colon follows it.

So the progress is made dependent on the production isLabel

isLabel ::= ident ":"

isLabel can parse the following text exactly, if a colon follows the identifier. Altogether, the grammar alternatives are therefore tied into the following IF construct:

IF( isLabel() )

ident ":" Statement

ELSE

StatementExpression ";"

END

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