[antlr-interest] architecture question

[Hugo]

hi,
i have a general question about performance,
i want to develop my own scripting language.

for performance i'll want to directly perform code operation when a rule 
is detected.
is it the best way or AST construction and tree parsing to execute the 
code is a better way ?

I case of directly executing the code how can i perform a 'if' cond 
block 'else' block 'end' rule ? the goal is to not perform parsing if 
the cond is not satisfied.

thanks in advance