Whitespace (programming language)


Whitespace is an esoteric programming language developed by Edwin Brady and Chris Morris at the University of Durham. It was released on 1 April 2003. Its name is a reference to whitespace characters. Unlike most programming languages, which ignore or assign little meaning to most whitespace characters, the Whitespace interpreter ignores any non-whitespace characters. Only spaces, tabs and linefeeds have meaning. A consequence of this property is that a Whitespace program can easily be contained within the whitespace characters of a program written in another language, except possibly in languages which depend on spaces for syntax validity such as Python, making the text a polyglot.
The language itself is an imperative stack-based language. The virtual machine on which the programs run has a stack and a heap. The programmer is free to push arbitrary-width integers onto the stack and can also access the heap as a permanent store for variables and data structures.

History

Whitespace was created by Edwin Brady and Chris Morris in 2002. Slashdot gave a review of this programming language on 1 April 2003.
The idea of using whitespace characters as operators for the C++ language was facetiously suggested five years earlier by Bjarne Stroustrup.

Syntax

Commands are composed of sequences of spaces, tab stops and linefeeds. For example, tab-space-space-space performs arithmetic addition of the top two elements on the stack.
Data is represented in binary using spaces and tabs, followed by a linefeed; thus, space-space-space-tab-space-tab-tab-linefeed is the binary number 0001011, which is 11 in decimal. All other characters are ignored and thus can be used for comments.
Code is written as an Instruction Modification Parameter followed by the operation. The table below shows a list of all the IMPs in Whitespace.
IMPMeaning
Stack Manipulation
Arithmetic
Heap Access
Flow Control
I/O

Each IMP is followed by one operation defined for that IMP, and a parameter if needed. The list of operations supported in Whitespace is:
IMPCommandParameterMeaning
NumberPush the number onto the stack
-Duplicate the top item on the stack
-Swap the top two items on the stack
-Discard the top item on the stack
-Addition
-Subtraction
-Multiplication
-Integer Division
-Modulo
-Store in heap
-Retrieve from heap
LabelMark a location in the program
LabelCall a subroutine
LabelJump to a label
LabelJump to a label if the top of the stack is zero
LabelJump to a label if the top of the stack is negative
-End a subroutine and transfer control back to the caller
-End the program
-Output the character at the top of the stack
-Output the number at the top of the stack
-Read a character and place it in the location given by the top of the stack
-Read a number and place it in the location given by the top of the stack

Sample code

The following is a commented Whitespace program that simply prints "Hello, world!", where each Space, Tab, or Linefeed character is preceded by the identifying comment "S", "T", or "L", respectively:
S S S T S S T S S S L T L S S S S S T T S S T S T L T L S S S S S T T S T T S S L T L S S S S S T T S T T S S L T L S S S S S T T S T T T T L T L S S S S S T S T T S S L T L S S S S S T S S S S S L T L S S S S S T T T S T T T L T L S S S S S T T S T T T T L T L S S S S S T T T S S T S L T L S S S S S T T S T T S S L T L S S S S S T T S S T S S L T L S S S S S T S S S S T L T L S S L L L
Note that 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.