是否有任何编程语言提供命名 function 的返回值的能力？

Question

Quite commonly while programming I find it necessary to document the value that a function returns. In Java/Scala world, you often use comments above the function to do this.

However, this can stand out in contrast to the first-class documentation that function parameters get in all languages. For example:

def exponent(base: Int, power: Int): Int

Here we have the signature for a method that raises base to the power power and returns... probably the result of that computation ? I know for certain it returns an Int , and it seems quite reasonable to infer that the return value is indeed the result of calculating base ^ power , but in many functions I've written and read it is not possible to infer the return value's semantic meaning quite so easily and you need to study the documentation and/or actually use the method to find out.

Which leads me to wonder, do any languages provide support for optionally declaring a semantic name for the return value?

def exponent(base: Int, power: Int): Int(exitCode)

A hah, Turns out this function actually returns an indication of whether the operation succeeded or failed: Look it is so clear right there in the method signature! My IDE could also intelligently create a variable with the same name when I call this method, a la:

// Typing in IntelliJ
exponent(5, 5)<TAB>

// Autocompletes to:
val exitCode = exponent(5, 5)

I'm not under any illusion that this is some sort of ground-breaking idea, but it seems like it could be generally useful, and I'm struck that I have never seen this concept implemented in any programming language.

Can you name any single programming language that does have this kind of semantic naming of return values?

Answer 1

In APL, for instance, the result of a function is declared as a variable. The function declaration in your example could be written like

exitCode ← base exponent power

in APL. However, a function with no side effects should always be named after the result it returns. If the function can fail I would use a value that is never returned on success, for instance -1 in this case.