The problem is that a function is a thing. A string is a different thing. Imagine if arrays were represented as comma delimited strings, and you had a function isArray to check if a string has the right format to represent an array. That would be ridiculous right? An array should be its own type. The same goes for functions. Representing functions as string names is just as crazy as representing arrays as comma delimited strings.

Though who am I kidding, PHP is also confused between numbers and arrays and strings, so I guess at least it's consistent that the language is thoroughly crazy.