Evaluating Nested Expressions in pigeon

[sham]

Hello

If we evaluate nested call expression like 

mul(add(2, mul(4, 6)), add(3, 5))

It is in-order traversal on evaluation space, programmatically.

How would I evaluate call expression

lt 2 3 45

Above expression is human readable but am not sure how do we evaluate programmatically.

 For operator lt expression with only 2 operands lt(2, 3) would only make sense to me.

Regards

 Sham