TREE-META

The TREE-META (or Tree Meta, TREEMETA) Translator Writing System is a compiler-compiler system for context-free languages originally developed in the 1960s. Parsing statements of the metalanguage resemble augmented Backus–Naur form with embedded tree-building directives. Unparsing rules include extensive tree-scanning and code-generation constructs. The TREE-META (or Tree Meta, TREEMETA) Translator Writing System is a compiler-compiler system for context-free languages originally developed in the 1960s. Parsing statements of the metalanguage resemble augmented Backus–Naur form with embedded tree-building directives. Unparsing rules include extensive tree-scanning and code-generation constructs. TREE-META was instrumental in the development of the On-Line System and was ported to many systems including the Univac 1108, GE 645, SDS-940, ICL 1906A, PERQ, and UCSD p-System. This is a complete example of a TREE-META program extracted (and untested) from the more complete (declarations, conditionals, and blocks) example in Appendix 6 of the ICL 1900 TREE-META manual. That document also has a definition of TREE-META in TREE-META in Appendix 3. This program is not just a recognizer, but also outputs the assembly language for the input. It demonstrates one of the key features of TREE-META, which is tree pattern matching. It is used on both the LHS (GET and VAL for example) and the RHS (ADD and SUB).