Architecture
Qi makes use of the logical notation of sequent calculus to define types. This type notation, under Qi's interpretation, is actually a Turing complete language in its own right. This notation allows Qi to assign extensible type systems to Common Lisp libraries and is thought of as an extremely powerful feature of the language.
Qi compiles sequent calculus to Qi Prolog (which is incorporated into the Qi environment) via the Abstract Unification Machine (AUM). The AUM acts as a functional programming analog to the Warren abstract machine generating virtual instructions from what is essentially an extended lambda calculus (see also Prolog#Implementation techniques). The Qi compiler maps AUM instructions to Common Lisp, and these the Lisp compiler compiles into byte code or machine code depending on the Lisp platform. The Qi environment also includes a compiler-compiler Qi-YACC which is used in the encoding of Qi to handle the parsing and reading of Qi code. Qi is thus bootstrapped or written (largely) in itself apart from a few Common Lisp functions.
Read more about this topic: Qi (programming Language)
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