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Muriel is an esoteric programming language designed by Matthew Westcott in 2001.


The name Muriel is an acronym that stands for Monumentally Useless Re-Iterative Execution Language.

Computational model

Like SMITH, Muriel has no traditional control structures. Instead, Muriel has a command to replace the currently running Muriel program with a given string, and run that instead. This leads to a programming method where a program must quine itself in order to perform any sort of loop.

General syntax

A Muriel program consists zero or more instructions separated by ; (semicolons).


a:0 Assign the integer variable a with the value 0. Integer variables can be any lowercase letter [a-z] and value can be any integer expression.
A:"Foo" Assign the string variable A with the value Foo. String variables can be any uppercase letter [A-Z] and value can be any string expression.
."Foo" Output Foo. Can be any string expression.
@".$0" Execute the Muriel program .$0. Can be any string expression. Variables in the current program are not passed down and control does not return to the parent program on completion.


If multiple expressions are chained, they are evaluated left to right. Brackets can be used to determine the order of operation ($1+1 is invalid but $(1+1) is "2").


123 Integer literal in decimal. Can be negative.
a Value of the integer variable a. Integer variables can be any lowercase letter [a-z].
1+2 Addition of two integer expressions.
4-2 Substraction. Unary minus is allowed (-x means 0-x).
2*2 Multiplication.
2=2 Equality test. 1 if true, 0 if false.
2>1 Greater than test. 1 if true, 0 if false.
2<3 Less than test. 1 if true, 0 if false.
#N Number represented by string expression N. Causes an error if N does not make sense as a number.
&N Length of string N.


"Bar" String literal. Valid escape sequences are \" for ", \n for new line and \\ for \.
A Value of the string variable A. String variables can be any uppercase letter [A-Z].
~ String received from user input.
"X"+"Y" Concatenation of two string expressions.
$n String representation of integer expression n.
%N,a,b Substring of N, starting at character a included (first character is 0) up to b excluded. Errors if numbers are out of range or a > b.
|N Replaces all ", \ and new lines in the string N by their respective escape sequences.

Computational class

There exists an interpreter for the language Bub written in Muriel. Since Bub is a small variant of Brainfuck, it ought to be possible to show through simulation and reduction that Muriel is Turing-complete as well.

See also

External resources