You were trying that right. If Inno Setup were using Pascal it would even work, but since it is based on a custom Pascal Script
language with limitation on declaring local constants, you can't do it that way. You must define your constant globally instead:
[Code]
const
MethodName = 'MyExec';
function MyExec(const _filename, _params, _dir: String): Boolean;
var
ResultCode: Integer;
begin
MyLog(MethodName, _filename);
// ... invoke Exec(), etc. ...
end;