Extensible Language One. An extensible language by B. Wegbreit of Harvard ca 1974. EL1 is internally somewhat Lisp -like, but fully typed with record s and pointers. The external syntax is ALGOL -like and extensible, supporting user-defined data structure s, control structures and operations. The parser is table-driven, with a modifiable set of productions. Used as the basis for the ECL operating system .
["Studies in Extensible Programming Languages", B. Wegbreit, Garland. Pub 1980].