TECO (), 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.
Description 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. The same essay in describing TECO coined the acronym YAFIYGI, meaning "You Asked For It You Got It" (in contrast to WYSIWYG).
Impact The EMACS editor originally started by David A. Moon and Guy L. Steele Jr. was implemented in TECO as a set of Editor MACroS. TECO became more widely used following a Digital Equipment Corporation (DEC) PDP-6 implementation developed at MIT's Project MAC in 1964. This implementation continuously displayed the edited text visually on a CRT screen, and was used as an interactive online editor. Later versions of TECO were capable of driving full-screen mode on various DEC RS-232 video terminals such as the VT52 or VT100. TECO was available for several operating systems and computers, including the PDP-1 computer, the PDP-8 (under OS/8), the Incompatible Timesharing System (ITS) on the PDP-6 and PDP-10, and TOPS-10 and TOPS-20 on the PDP-10. A version of TECO was provided with all DEC operating systems; the version available for RT11 was able to drive the GT40 graphics display while the version available for RSTS/E was implemented as a multi-user run-time system and could be used as the user's complete operating environment; the user never actually had to exit TECO. The VTEDIT (Video Terminal Editor) TECO macro was commonly used on RSTS/E and VAX systems with terminals capable of direct-cursor control (e.g. VT52 and VT100) to provide a full-screen visual editor similar in function to the contemporaneously developed Emacs. TECO continues to be included in OpenVMS by VSI, and is invoked with the EDIT/TECO command. A descendant of the version DEC distributed for the PDP-10 is still available on the Internet, along with several partial implementations for the MS-DOS/Microsoft Windows environment.
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