More Stack Words

Here are a few more useful built-in words for the stack:
WordAction
.S

Displays the number and contents of the stack without altering it.

OVER

1 2 OVER .S
becomes
<3> 1 2 1

NIP

1 2 NIP .S
becomes
<1> 2

TUCK

1 2 TUCK .S
becomes
<3> 2 1 2

DEPTH

Puts the number of items on the stack. For example,

"Hello" "Smojo" DEPTH .S
becomes
<3> "Hello" "Smojo" 2

The Return Stack

In addition to the main stack, Smojo also has a "return" stack. This is often used for temporary storage of items. Some words:
WordAction
.R

Displays the number and contents of the return stack without altering it.

>R

Pops the top of the stack and pushes it onto the return stack.

R>

Pops the top of the return stack and pushes it onto the main stack.

R@

Pushes the top of the return stack (without popping it) onto the main stack.

RDROP

Drops an item from the top of the return stack.

Below are some illustration on what happens in the main stack and return stack for 
>R
,
R>
,
R@
and
RDROP
.

Quiz

Question 1

Rewrite the advanced stack words:

NIP
,
OVER
,
TUCK
,
R@
and
RDROP
in terms of the basic stack and return stack words.



Question 2

Consider the word 
ROT
("rotate") that behaves this way:
1 2 3 ROT
becomes
2 3 1

Write this word in terms of the words you know.

Question 3

Consider the word 
-ROT
"undoes"
ROT
:
2 3 1 -ROT
becomes
1 2 3

Write this word in terms of the words you know.



Question 4

Write the words 
{{
and
}}
that counts the number of items between them, without altering the stack. For example:
{{ 1 2 "mini" 3 }}
becomes
1 2 "mini" 3 4



Next: Conditionals