Wow... this wasn't easy to convert to a function. Probably why Richard never did to begin with. Anyway if you want to try this go ahead. I'm thinking the first issue you will run into is functions with required parameters. Also, make sure you put the function name in quotes.
Code:
? Isfunction("FOO")
? Isfunction("Bar")
Function Foo()
exit 0
EndFunction
Function IsFunction($FN)
Dim $RC
$RC=execute("$" + "IsFunction=iif(CSTR(" + $FN + ")='" + $FN +"',0,1)")
EndFunction
