User defined functions within the grammer

[Ilan Khdavi]

Hi,

I want to use JAVACC for parsing and evaluating expressions (involving
operators and functions).
I understand that the grammar should be known prior to compilation.
However our specification requires that the end user will be able to
write its own functions as part of the expression.
How can I identify "user functions" as tokens although they don't appear
in the grammar? How can I evaluate them?
Is there any predefined grammar for this purpose?

Thanks in advance
Ilan

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