TECO is a powerful, yet underappreciated, programming language. It was originally developed in the early 1960s at the MIT AI Lab by Dan Murphy, Dick Grune, and Bob Corbett. It is an interpreted language, which means that programs are not compiled, but are instead read and executed by a TECO interpreter.
TECO is known for its extreme flexibility and for being "the programmer's editor." It is a full-featured text editor, but it can also be used to write programs. In fact, many of the features that make TECO such a great editor also make it a great language for writing programs. For example, TECO has a powerful macro system that allows you to define new commands and even new programming languages.
TECO is also known for its "string processing" capabilities. It has a rich set of string manipulation operators that make it easy to write programs that process text. This is one of the reasons that TECO was used to write the first version of the Emacs text editor.
Despite its many strengths, TECO is not a widely used language. This is partly due to its unusual syntax, which can be daunting to newcomers. But it is also because TECO is not well-suited for "industrial-strength" programming. It is a great language for writing small programs or for prototyping new ideas, but it is not suited for large, complex programs.
If you are looking for a powerful, yet underutilized, programming language, TECO is definitely worth checking out.