execution of nested loop joins

Hi all,

nodeNestloop.c executes nested loop joins. After getting a pair of inner 
and outer it test the inner and outer tuples to see if they satisfy the 
node's qualification using function ExecQual(joinqual, econtext, false).

ExecQual evaluates join conditions one at a time.It captures one 
condition and passes it to function ExecEvalExpr which is actually a 
macro that invokes another function evalfunc(a method of ExprState 
structure).

I am not getting implementation and use of this evalfunc function. Is 
this function used to evaluate the join condition or not. If yes, then 
how it does this.

thanx
esha