Forth 2012: ?DUP

6.1.0630

?DUP

question-dupe

CORE

( x -- 0 | x x )

Duplicate x if it is non-zero.

Testing:

T{ -1 ?DUP -> -1 -1 }T
T{ 0 ?DUP -> 0 }T
T{ 1 ?DUP -> 1 1 }T

Forth 2012
- Forth 2012
Glossary
?DUP
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- #S
- '
- (
- *
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- */MOD
- +
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- 0=
- 1+
- 1-
- 2!
- 2*
- 2/
- 2@
- 2DROP
- 2DUP
- 2OVER
- 2SWAP
- :
- ;
- <
- <#
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- >BODY
- >IN
- >NUMBER
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- ?DUP
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- ABORT
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- ABS
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- BEGIN
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- C!
- C,
- C@
- CELL+
- CELLS
- CHAR
- CHAR+
- CHARS
- CONSTANT
- COUNT
- CR
- CREATE
- DECIMAL
- DEPTH
- DO
- DOES>
- DROP
- DUP
- ELSE
- EMIT
- ENVIRONMENT?
- EVALUATE
- EXECUTE
- EXIT
- FILL
- FIND
- FM/MOD
- HERE
- HOLD
- I
- IF
- IMMEDIATE
- INVERT
- J
- KEY
- LEAVE
- LITERAL
- LOOP
- LSHIFT
- M*
- MAX
- MIN
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- POSTPONE
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- R>
- R@
- RECURSE
- REPEAT
- ROT
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- SM/REM
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- SPACES
- STATE
- SWAP
- THEN
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