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[[File:Whitespace in vim2.png|right|206px|thumb|Whitespace [[hello world program]] with syntax highlighting {{legend|#0000ab|tabs}} {{legend|#ab0000|spaces}}]] <!-- make SVG file -->
'''Whitespace''' is an [[esoteric programming language|esoteric]] [[programming language]] with [[syntax]] where ''only'' [[whitespace characters]] ([[Space character|space]], [[Tab character|tab]] and [[linefeednewline]]) have meaning {{endash}} contrasting typical languages that largely ignore whitespace characters.
<ref name="whitespace">{{cite web|url=http://compsoc.dur.ac.uk/whitespace/tutorial.php|title=Whitespace|website=Compsoc|access-date=2015-12-08|url-status=dead|archive-url=https://web.archive.org/web/20150618184706/http://compsoc.dur.ac.uk/whitespace/tutorial.php|archive-date=18 June 2015}}</ref><ref name=parker>{{cite book|title=Humble Pi: a comedy of maths errors|publisher=Allen Lane|date=2019|first=Matt|last=Parker|author-link=Matt Parker|ISBN=978-0-241-36023-1|page=21}}</ref>
The programmer can push arbitrary-width [[integer]] values onto a [[Stack (abstract data type)|stack]] and access a [[dynamic memory allocation|heap]] to store data.
An [[Interpreter (computing)|interpreter]], andalong with its [[HaskelHaskell]] source code, is provided by the Whitespace creators.
== History ==
== Syntax ==
Whitespace defines a command as a sequencessequence of whitespace characters. For example, <code>[Tab][Space][Space][Space]</code> performs arithmetic addition of the top two elements on the stack.
A command is written as an instruction modification parameter (IMP) followed by an operation and then any parameters.
|-
! IMP !! Operator !! Parameter !! Meaning
!Minimum size of the stack required*
|-
| [Space] || [Space] || Number || Push the number onto the stack
|0
|-
| [Space] || [LF][Space] || - || Duplicate the top item on the stack
|1
|-
| [Space] || [Tab][Space] || Number ''n''|| Copy the nth item on the stack (given by the argument) onto the top of the stack**
|''n''+1
|-
| [Space] || [LF][Tab] || - || Swap the top two items on the stack
|2
|-
| [Space] || [LF][LF] || - || Discard the top item on the stack
|1
|-
| [Space] || [Tab][LF] || Number ''n''|| Slide n items off the stack, keeping the top item**
|may be less than '''''n''+1''',
but at least 1 item
(top of the stack)
is required
|-
| [Tab][Space] || [Space][Space] || - || Addition
|2
|-
| [Tab][Space] || [Space][Tab] || - || Subtraction
|2
|-
| [Tab][Space] || [Space][LF] || - || Multiplication
|2
|-
| [Tab][Space] || [Tab][Space] || - || Integer Divisiondivision
|2 (top may not be 0)
|-
| [Tab][Space] || [Tab][Tab] || - ||[[Modulo operation|Modulo]]
|2 (top may not be 0)
|-
| [Tab][Tab] || [Space] || - || Store in heap
|2
|-
| [Tab][Tab] || [Tab] || - || Retrieve from heap
|1
|-
| [LF] || [Space][Space] || Label || Mark a ___location in the program
|0
|-
| [LF] || [Space][Tab] || Label || Call a subroutine
|0
|-
| [LF] || [Space][LF] || Label || Jump to a label
|0
|-
| [LF] || [Tab][Space] || Label || Jump to a label if the top of the stack is zero
|1
|-
| [LF] || [Tab][Tab] || Label || Jump to a label if the top of the stack is negative
|1
|-
| [LF] || [Tab][LF] || - || End a subroutine and transfer control back to the caller
|0 ''(callstack: 1)''
|-
| [LF] || [LF][LF] || - || End the program
|0
|-
| [Tab][LF] || [Space][Space] || - || Output the character at the top of the stack
|1
|-
| [Tab][LF] || [Space][Tab] || - || Output the number at the top of the stack
|1
|-
| [Tab][LF] || [Tab][Space] || - || Read a character and place it in the ___location given by the top of the stack
|1
|-
| [Tab][LF] || [Tab][Tab] || - || Read a number and place it in the ___location given by the top of the stack
|1
|}
<nowiki>*</nowiki>Due to Haskell being lazily evaluated, the effect of the stack being too small may only show when, for example, invoking the ''outputting a number'' side-effect.
The ''copy'' and ''slide'' operations were added in Whitespace 0.3.<ref name="whitespace"/> ▼
▲<nowiki>**</nowiki>The ''copy'' and ''slide'' operations were added in Whitespace 0.3.<ref name="whitespace" />
=== Comments ===
For example:
* [space][tab][space][space][tab][space][tab][tab][linefeed] (STSSTSTTL) is positive since it starts with <code>space</code> and represents 1001011 in binary, which is 75 in decimal.
* [tab][tab][tab][space][space][tab][space][linefeed] (TTTSSTSL) is negative since it starts with <code>tab</code> and represents -110010 in binary which is −50 in decimal.
=== Labels ===
A label is used for [[control flow]]. It is a <code>linefeed</code>-terminated sequence of <code>space</code>and <code>tab</code> characters. As there is only one namespace, all labels must be unique.
<ref name="whitespace"/>
==Sample code==
<code><span style="color:#ffffff;background:#ff9999">space</span></code>,
<code><span style="color:#ffffff;background:#9999ff">tab</span></code>, and <code>linefeed</code>.
{{not a typo start}}
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T<span style="background:#9999ff">	Tab;</span>L S<span style="background:#ff9999"> {{sp}}</span>S<span style="background:#ff9999"> {{sp}}</span>:Output_'!';_L L L:End_the_program
{{not a typo end}}
When Whitespace source code is displayed in some browsers, the horizontal spacing produced by a tab character is not fixed, but depends on its ___location in the text relative to the next [[Tab key#HTML|horizontal tab stop]]. Depending on the software, tab characters may also get replaced by the corresponding variable number of space characters.
[[Category:Programming languages created in 2002]]
[[Category:Stack-oriented programming languages]]
{{Esoteric programming languages}}
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