1. Cat's Eye Technologies
  2. Maentwrog

Overview

The Maentwrog Programming Language

This is the reference distribution for the Maentwrog programming language, designed and implemented in 1993.

This distribution contains the reference interpreter, written in ANSI C, a rudimentary specification (below) and some example Maentwrog programs. It also contains a few other miscellaneous contemporaneous C programs by the author.

The current released version of the Maentwrog distribution is version 1.1 revision 2014.0923.

Specification

This is a rudimentary specification for the Maentwrog programming language.

This information, and the example programs in this distribution, were taken from the esolangs.org wiki page for Maentwrog, written by User:Marinus and (like all esowiki articles) placed in the public domain. Thanks Marinus!

Syntax

A Maentwrog program consists of a series of words, separated by whitespace. Words can contain any character except whitespace. The way these words are executed depends on the character they begin with.

  • A word that consists of digits is taken as an integer and pushed. A minus sign may be used to make negative numbers, so 25 and -14 are words that push 25 and -14 onto the stack. Extra characters at the end of the word are allowed, so 25abc and 25.14 both also push 25.
  • A word that isn't a number is treated as either a function or a variable. If the word is defined as a function, it is executed; if it's a variable, its current value is pushed to the stack. Using an undefined word results in an error, though this doesn't stop further execution of the program.
  • To define a word as a function, use the syntax : new-word words to execute ; (as in Forth). Redefining a word is not allowed, and neither are nested function definitions.
  • To define a word as a variable, use the syntax *varname. This must be done before using a variable.

Additionally, words (except number words) can take one of a list of prefixes, changing how the word is executed.

Prefix   Action               Example     Result
-----    ------               -------     ------
=        Assign to variable   =foo        A value popped from the stack is
                                          assigned to the variable foo.
@        If                   @bye        Pop value, stop the program (see
                                          predefined words) if it isn't 0.
[        While                [xyz        Pop value, if it's not 0 execute
                                          word xyz, then pop another value
                                          and do it again; continue until a
                                          0 is popped.
$        Repeat               $.          Pop value, then output that many
                                          values from the stack.

Predefined words

Word           Stack effect   Description
----           ------------   -----------
bye                           Stop program immediately.
rem ... ;                     Comment. (Ignore all words between rem and ;.)
: word ... ;                  Define a new word.
debug                         Turn on debugging (outputs all words executed).
vars                          Output a list of currently defined variables
                                and their values.
words                         Output a list of currently defined words.
alloc            n | ptr      Allocate memory for n C longs, returns a pointer.
free           ptr | -        Free memory at pointer.
size             - | n        Push stack size.
dup              a | a a      Duplicate top of stack.
swap           a b | b a      Swap the two topmost stack values.
pop              a | -        Remove top value from stack.
get            ptr | value    Push value at pointer to stack (C `*ptr`).
put            p v | -        Store value at pointer (C `*ptr = val`).
rnd              - | n        Push random value.
>              a b | (a>b)    Push 1 if a is greater than b, else 0.
<              a b | (a<b)    Push 1 if a is less than b, else 0.
==             undefined      Undefined.
.                n | -        Pop a value, output as integer, adding a newline.
..               n | -        Pop a value, output as an ASCII character.
mod            a b | (a%b)    Modulo.
+              a b | (a+b)    Addition.
-              a b | (a-b)    Subtraction.
*              a b | (a*b)    Multiplication.
/              a b | (a/b)    Division, result is rounded towards 0.