Whitespace is an esoteric programming language with syntax where only whitespace characters (space, tab and linefeed) have meaning – contrasting typical languages that largely ignore whitespace characters. [1][2]
As a consequence of its syntax, Whitespace source code can be contained within the whitespace of code written in a language that ignores whitespace – making the text a polyglot.[2]
Whitespace is an imperative, stack-based language. The programmer can push arbitrary-width integer values onto a stack and access a heap to store data.
An interpreter, along with its Haskell source code, is provided by the Whitespace creators.
History
editEdwin Brady and Chris Morris, who also developed the Kaya and Idris languages, created Whitespace in 2002 at the University of Durham. Slashdot published a review on April Fool's Day 2003.[3]
The idea of using whitespace characters as operators for the C++ language had been facetiously suggested five years earlier by Bjarne Stroustrup.[4]
Syntax
editWhitespace defines a command as a sequences of whitespace characters. For example, [Tab][Space][Space][Space] 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. [1]
IMP sequences include:
| 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:[1]
| IMP | Operator | Parameter | Meaning |
|---|---|---|---|
| [Space] | [Space] | Number | Push the number onto the stack |
| [Space] | [LF][Space] | - | Duplicate the top item on the stack |
| [Space] | [Tab][Space] | Number | Copy the nth item on the stack (given by the argument) onto the top of the stack |
| [Space] | [LF][Tab] | - | Swap the top two items on the stack |
| [Space] | [LF][LF] | - | Discard the top item on the stack |
| [Space] | [Tab][LF] | Number | Slide n items off the stack, keeping the top item |
| [Tab][Space] | [Space][Space] | - | Addition |
| [Tab][Space] | [Space][Tab] | - | Subtraction |
| [Tab][Space] | [Space][LF] | - | Multiplication |
| [Tab][Space] | [Tab][Space] | - | Integer division |
| [Tab][Space] | [Tab][Tab] | - | Modulo |
| [Tab][Tab] | [Space] | - | Store in heap |
| [Tab][Tab] | [Tab] | - | Retrieve from heap |
| [LF] | [Space][Space] | Label | Mark a location in the program |
| [LF] | [Space][Tab] | Label | Call a subroutine |
| [LF] | [Space][LF] | Label | Jump to a label |
| [LF] | [Tab][Space] | Label | Jump to a label if the top of the stack is zero |
| [LF] | [Tab][Tab] | Label | Jump to a label if the top of the stack is negative |
| [LF] | [Tab][LF] | - | End a subroutine and transfer control back to the caller |
| [LF] | [LF][LF] | - | End the program |
| [Tab][LF] | [Space][Space] | - | Output the character at the top of the stack |
| [Tab][LF] | [Space][Tab] | - | Output the number at the top of the stack |
| [Tab][LF] | [Tab][Space] | - | Read a character and place it in the location given by the top of the stack |
| [Tab][LF] | [Tab][Tab] | - | Read a number and place it in the location given by the top of the stack |
The copy and slide operations were added in Whitespace 0.3.[1]
Comments
editCharacters other than space, tab and linefeed are ignored and thus can be used for comments.
Numbers
editA numeric value is represented as a sequence of space and tab characters that represent 0 and 1 respectively and terminated by a linefeed. The first character represents the sign of the value – space for positive and tab 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
spaceand represents 1001011 in binary, which is 75 in decimal. - [tab][tab][tab][space][space][tab][space][linefeed] (TTTSSTSL) is negative since it starts with
taband represents -110010 in binary which is −50 in decimal.
Labels
editA label is used for control flow. It is a linefeed-terminated sequence of spaceand tab characters. As there is only one namespace, all labels must be unique.
[1]
Sample code
editThe following source code is for a Whitespace "Hello, world!" program. For clarity, it is annotated with S, T and L before each
space,
tab, and linefeed.
S S S T S S T S S S L:Push_+1001000=72='H'_onto_the_stack T L S S :Output_'H';_S S S T T S S T S T L:Push_+1100101=101='e'_onto_the_stack T L S S :Output_'e';_S S S T T S T T S S L:+1101100=108='l' T L S S S S S T T S T T S S L:+1101100=108='l' T L S S S S S T T S T T T T L:+1101111=111='o' T L S S S S S T S T T S S L:+101100=44=',' T L S S S S S T S S S S S L:+100000=32=Space T L S S S S S T T T S T T T L:+1110111=119='w' T L S S S S S T T S T T T T L:+1101111=111='o' T L S S S S S T T T S S T S L:+1110010=114='r' T L S S S S S T T S T T S S L:+1101100=108='l' T L S S S S S T T S S T S S L=+1100100=100='d' T L S S S S S T S S S S T L:+100001=33='!' T L S S :Output_'!';_L L L:End_the_program
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 horizontal tab stop. Depending on the software, tab characters may also get replaced by the corresponding variable number of space characters.
References
edit- ^ a b c d e "Whitespace". Compsoc. Archived from the original on 18 June 2015. Retrieved 8 December 2015.
- ^ a b Parker, Matt (2019). Humble Pi: a comedy of maths errors. Allen Lane. p. 21. ISBN 978-0-241-36023-1.
- ^ Timothy (1 April 2003). "New Whitespace-Only Programming Language". Slashdot. Retrieved 23 January 2014.
- ^ Stroustrup, Bjarne. "Generalizing Overloading for C++2000" (PDF). Florham Park, NJ, USA: AT&T Labs. Retrieved 23 January 2014.
External links
edit- Official website
- Release announcement on Slashdot
- The Whitespace Corpus A collection of interpreters, compilers, and programs for Whitespace
- Collection of Whitespace interpreters in various script languages
- Acme::Bleach A Perl module that rewrites the body of your module to a whitespace-only encoding ("for really clean programs").