Gidubba/readme.md

Gidubba
========

Gidubba (Sumerian for 'stylus') is a simple line editor for the
Thingamajig computer architecture. Its git repository can be found at
https://ahti.space/git/crazyettin/Gidubba and that of Thingamajig at
https://ahti.space/git/crazyettin/Thingamajig.

System requirements
-------------------

Gidubba uses a terminal with local echo at address FFFF, and optionally
a character printer at address FFFE and a punched tape reader and punch
or a casette drive at FFFD. Do not be afraid to modify the code yourself
if your setup requires it!

Format
------

Gidubba works with texts consisting of lines and terminated with an
end-of-file (^Z). The lines consist of at most 256 characters terminated
by a newline of a carriage return (^M) followed by a line feed (^J),
included in the character count. Note that any characters following the
last newline and preceding the end-of-file are ignored.

Usage
-----

The commands are individual letters that can be followed by one or two
arguments separated by a comma, all case-insensitive. The first argument
is a line number between 0 and FFFF and the second a range of lines
between 0 and FF. To append lines, insert or copy them to any line
number after the text or to the shortcut hash (#); in other commands
line numbers or parts of a range after the text are ignored. Instead of
a predetermined range a prompt to insert the next line appears
automatically after the previous one has been committed.

Commands with a single argument:
  * I: Insert lines

Commands with two arguments:
  * C: Copy to the mark
  * D: Delete lines
  * L: List lines

Commands with no arguments:
  * M: Set a mark
  * P: Print
  * R: Read from the tape reader or casette drive
  * W: Write to the tape punch or casette drive

A delete (^?) discards the preceding character and outputs an underscore
to the terminal. An escape (^[) discards the contents of the current
command or line and outputs a backslash and a newline to the terminal.
A carriage return (^M) or a line feed (^J) inputs a newline that commits
the current command or line. An end-of-file (^Z) discards the current
command and halts the computer or discards the current line and returns
to the command prompt.