Stack operations

Operations for manipulating values on the stack.

Overview

Instruction	Signature	Description
`dup`	`(a -- a a)`	Duplicate top
`dup2`	`(a b -- a b a b)`	Duplicate top two
`dupd`	`(a b -- a a b)`	Duplicate second
`drop`	`(a --)`	Remove top
`drop2`	`(a b --)`	Remove top two
`swap`	`(a b -- b a)`	Exchange top two
`swap2`	`(a b c d -- c d a b)`	Exchange top pairs
`swapd`	`(a b c -- b a c)`	Swap under top
`over`	`(a b -- a b a)`	Copy second to top
`over2`	`(a b c d -- a b c d a b)`	Copy second pair
`overd`	`(a b c -- a b a c)`	Copy second under top
`rot`	`(a b c -- b c a)`	Rotate three
`nip`	`(a b -- b)`	Remove second
`nipd`	`(a b c -- a c)`	Remove second under top
`tuck`	`(a b -- b a b)`	Copy top under second
`pick`	`(... n -- ... val)`	Copy nth value
`roll`	`(... n -- ...)`	Move nth to top
`clear`	`(... --)`	Remove all
`depth`	`(... -- ... n)`	Count values

Duplication

dup

Duplicates the top value on the stack.

Signature: (a -- a a)

5 dup + // 10

dup2

Duplicates the top two values.

Signature: (a b -- a b a b)

1 2 dup2 // Stack: [1, 2, 1, 2]

dupd

Duplicates the second value, keeping top on top.

Signature: (a b -- a a b)

Removal

drop

Removes the top value from the stack.

Signature: (a --)

1 2 3 drop // Stack: [1, 2]

drop2

Removes the top two values from the stack.

Signature: (a b --)

Swapping

swap

Exchanges the top two values.

Signature: (a b -- b a)

1 2 swap // Stack: [2, 1]

swap2

Exchanges the top two pairs of values.

Signature: (a b c d -- c d a b)

swapd

Swaps the second and third values, keeping top on top.

Signature: (a b c -- b a c)

Copying

over

Copies the second value to the top.

Signature: (a b -- a b a)

1 2 over // Stack: [1, 2, 1]

over2

Copies the second pair to the top.

Signature: (a b c d -- a b c d a b)

overd

Copies the second value, keeping top on top.

Signature: (a b c -- a b a c)

Rotation

rot

Rotates the top three values, moving third to top.

Signature: (a b c -- b c a)

1 2 3 rot // Stack: [2, 3, 1]

Other operations

nip

Removes the second value, keeping top.

Signature: (a b -- b)

1 2 nip // Stack: [2]

nipd

Removes the second value, keeping top and third.

Signature: (a b c -- a c)

tuck

Copies the top value under the second.

Signature: (a b -- b a b)

pick

Copies the nth value (0-indexed from top) to the top.

Signature: (... n -- ... val)

1 2 3 4 2 pick // Copies index 2 (value 2) to top

roll

Moves the nth value to the top, shifting others down.

Signature: (... n -- ...)

1 2 3 4 2 roll // Moves index 2 (value 2) to top

clear

Removes all values from the stack.

Signature: (... --)

depth

Pushes the number of values on the stack.

Signature: (... -- ... n)

1 2 3 depth // Stack: [1, 2, 3, 3]