Tutorial: The Stack

sclin is a stack-based language, meaning that computations in sclin are primarily centered around a stack. (Wow, how insightful!) Whereas in other languages, you might do:

(6 + 8) * 5

In sclin, you might instead do:

6 8 + 5 *

Here's what the stack goes through:

Token	Meaning	Stack
6	push 6	6
8	push 8	6 8
+	pop top 2 items, add, push result	14
5	push 5	14 5
*	pop top 2 items, multiply, push result	70

The stack serves as a way to both return and store data.

Stack Combinators

On its own, the stack doesn't have much use. But stack combinators allow you to manipulate the stack, opening up a whole variety of options for stack-based computation. For example, let's say you wanted to write:

10 / (8 - 6)

In sclin, you could write:

10 8 6 - /

But you could also write:

8 6 - 10 swap /

Or if you wanted to get really unnecessarily fancy:

6 8 10 rev - /

The "elementary" stack combinators are dup (a -> a a), pop (a ->), swap (a b -> b a), rot (a b c -> b c a), and rot_ (a b c -> c a b). Here are the combinators, arranged by variations:

Elementary	Alters top items	Alters entire stack	Alters based on index
dup	dupd over ddup edup	dups	pick
pop	nip ppop qpop	clr	nix
swap	swapd tuck	rev	trade
rot			roll
rot_			roll_

Stack combinators are comparable to combinators found in functional programming languages. For example, flip in Haskell:

flip f x y = f y x
flip (-) 5 1 -- => -4

Is the same as 5 1 swap - in sclin.