Recursion using only global variables

Question

For the cause of simplicity, Smallbasic has only global variables. It does not have locals or parameters.

Although this makes it simpler to teach or learn it, it also complicates some matters, like recursive functions. I had a hard time creating a simple recursive function in smallbasic and had to use a manual stack. This works but it makes it more complicated and contradicts the initial main goal of simplicity!

This is how i can write the factorial:

n = 5
ind = 1
fact()
TextWindow.WriteLine("fact(5)=" + f)

Sub fact
  If n = 1 Then
    f = 1
  Else
    ind = ind+1
    keepn[ind] = n
    n = n-1
    fact()
    f = f * keepn[ind]
    ind = ind-1
  EndIf
EndSub

Note: I wrote it just now and it could have errors.
You see the picture. I'm manually creating a stack and using it to simulate local variable and use it for recursion.

Is there an easy way to create this recursive function?

score 2 · Accepted Answer · answered Aug 18 '14 at 17:33

I think you do have to resort to global variables to write a recursive function in SmallBasic.

I'd agree that SmallBasic's lack of function arguments is quite limiting and often makes a supposedly simple programming language quite complex to use in practice.

SmallBasic's library however is great for beginners, making it significantly easier to put things on the screen than enterprise frameworks like WinForms or WPF. The library, SmallBasicLibrary.dll, can be easily loaded into other .Net languages including VB.Net, C# and F#. Simply create a console application and add a reference to the library and then use import/using/open against the Library namespace.

While teaching my kids programming I started with SmallBasic, they loved the Turtle functionality, but then quickly switched to F# which has first-class support for functions and far less ceremony when compared to VB.Net or C#. Having to explain public static void Main to a 7yo before they could print "Hello World" just wasn't an attractive option to me.

As an experiment I've also created an alternative SmallBasic compiler implementation which you may find interesting as it includes support for function arguments, tuples and pattern matching.

score 1 · Answer 2 · answered Feb 08 '16 at 19:22

I think it's worth noting that creating a recursive function in this way - i.e. with only global variables, using a stack - is very educational in its own right. This is closer to the way assembly works, so from that perspective having to do things this way could actually be considered a feature...

Recursion using only global variables

2 Answers2