It originated at the Massachusetts Institute of Technology's (MIT) Project MAC[1] (from which it derived its prefix) in the late 1960s and was based on Lisp 1.5.
Maclisp also employed reader macros to make more readable input and output, termed input/output (I/O).
were added which in other language systems would typically correspond to major release numbers.
The SHRDLU blocks-world program was written in Maclisp, and so the language was in widespread use in the artificial intelligence (AI) research community through the early 1980s.
Later additions included: arrays, which were never first-class data types; arbitrary-precision integers (bignums); strings; and tuples.
The Ncomplr compiler (mid-1970s) introduced fast numeric support to Lisp languages, generating machine code (instructions) for arithmetic rather than calling interpretive routines which dispatched on data type.
The original version was limited by the 18-bit word memory address of the PDP-10, and considerable effort was expended in keeping the implementation lean and simple.