[uticus]

i mean that's cool, but from my background i would say since the input is "variable", assign it to a named variable and run the function with the variable assigned to 2, then again with it assigned to 4. that's doable in most any REPL.

or even take the function, and map a range of values to the function, to get a range of outputs. again, doable in most REPLs where the language supports some sort of mapping syntax.

can you help me understand what makes this unique? i'm not an APL user, so maybe it's just a different mindset altogether that i'm missing.

[7thaccount]

APL was one of the first interactive environments along with Lisp. They've had this back when you had a typewriter with a rotating ball with the symbols connected to the time share computer. So you'd type an expression on the typewriter, computer would run it, and it would be printed on actual paper lol.

With APL you can also do the stuff you're referring to by creating a function and mapping it to a list of numbers. If you're familiar with REPLs, the experience is similar.