TECO (text editor)

TECO (ˈtiːkoʊ), short for Text Editor & Corrector, is both a character-oriented text editor and a programming language, that was developed in 1962 for use on Digital Equipment Corporation computers, and has since become available on PCs and Unix. Dan Murphy developed TECO while a student at the Massachusetts Institute of Technology (MIT). According to Murphy, the initial acronym was Tape Editor and Corrector because "punched paper tape was the only medium for the storage of program source on our PDP-1. There was no hard disk, floppy disk, magnetic tape (magtape), or network." By the time TECO was made available for general use, the name had become "Text Editor and Corrector", since even the PDP-1 version by then supported other media. It was subsequently modified by many other people and is a direct ancestor of Emacs, which was originally implemented in TECO macros. TECO is not only an editor but also an interpreted programming language for text manipulation. Arbitrary programs (called "macros") for searching and modifying text give it great power. Unlike regular expressions, however, the language was imperative, though some versions had an "or" operator in string search. TECO does not really have syntax; each character in a program is an imperative command, dispatched to its corresponding routine. That routine may read further characters from the program stream (giving the effect of string arguments), change the position of the "program counter" (giving the effect of control structures), or push values onto a value stack (giving the effect of nested parentheses). But there is nothing to prevent operations like jumping into the middle of a comment, since there is no syntax and no parsing. TECO ignores case and whitespace (except tab, which is an insertion command). A satirical essay on computer programming, Real Programmers Don't Use Pascal, suggested that a common game for TECO fans was to enter their name as a command sequence, and then try to work out what would happen.