gBASIC. `help` for prompt commands, `quit` to leave.
> double(21)
runtime error at <prompt>:1:1: invalid function call: double
> function double(n)
...   return n * 2
... end function
> double(21)
42
> n = 5
> double(n)
10
> double(2 + 3)
10
> double(double(3))
12
> function double(n)
...   return n * 10
... end function
> double(21)
210
> function ask(question as string)
parse error at <prompt>:1:23: syntax error, unexpected AS, expecting RPAREN
> quit
Your program was not saved; `recover` will bring it back next time.
