Editing Whitespace (programming language) (section)

== Syntax ==

Whitespace defines a command as a sequences 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.
<ref name="whitespace" /> 

IMP sequences include:

{| class="wikitable"
|-
! IMP !! Meaning
|-
| [Space] || Stack Manipulation
|-
| [Tab][Space] || Arithmetic
|-
| [Tab][Tab] || Heap Access
|-
| [LineFeed] || Flow Control
|-
| [Tab][LineFeed] || I/O
|}

Operator sequences, organized by IMP, include:<ref name="whitespace"/>

{| class="wikitable"
|-
! 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 division
|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.

<nowiki>**</nowiki>The ''copy'' and ''slide'' operations were added in Whitespace 0.3.<ref name="whitespace" />

=== Comments ===

Characters other than <code>space</code>, <code>tab</code> and <code>linefeed</code> are ignored and thus can be used for comments. 

=== Numbers ===

A numeric value is represented as a sequence of <code>space</code> and <code>tab</code> characters that represent 0 and 1 respectively and terminated by a <code>linefeed</code>. The first character represents the [[Sign (mathematics)|sign]] of the value {{endash}} <code>space</code> for positive and <code>tab</code> for negative. Subsequent characters before the terminator represent the binary digits of a value.

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"/>