I'm currently re-working a BASIC I've created (a byte-code interpreter) and can't decide if I will include an eval function with it. I'm having doubts about its usefulness.
I can think of 2 uses for an eval functionality:
- It seems tailor-made for a calculator application. But I sincerily think a true developer would rather code it by himself.
- It would allow inputting a formula when the user is asked to supply some number. Could be handy. Although this sounds nice, I can't remember ever having seen any InputBox offering such functionality.
My question then is:
What are the practical uses of eval as part of a general purpose programming language like BASIC?
Searching this forum I found this opinion by S.Lott about the eval function (albeit in Python).
Should I even bother investigating the usefulness of eval?
Using eval is weak, not a clearly bad practice.
1.It violates the "Fundamental Principle of Software". Your source is not the sum total of what's executable. In addition to your source, there are the arguments to eval, which must be clearly understood. For this reason, it's the tool of last resort.
2.It's usually a sign of thoughtless design. There's rarely a good reason for dynamic source code, built on-the-fly. Almost anything can be done with delegation and other OO design techniques.
3.It leads to relatively slow on-the-fly compilation of small pieces of code. An overhead which can be avoided by using better design patterns.