test expr with perl-supplied functions

hello('dad')=hi, dad! lc('DAD')=dad lc(ONE)=1 sprintf('1+1=%d', TWO)=1+1=2

test expr with user-defined functions

registered_func('self')=self hello_string()=hello! arglist()=[] arglist('')=[] arglist('','')=[][] arglist('a','b')=[a][b]