System Description: Twelf — A Meta-Logical Framework for Deductive Systems

Twelf is a meta-logical framework for the specification, implementation, and meta-theory of deductive systems from the theory of programming languages and logics. It relies on the LF type theory and the judgments-as-types methodology for specification [HHP93], a constraint logic programming interpreter for implementation [Pfe91], and the meta-logic M2 for reasoning about object languages encoded in LF [SP98]. It is a significant extension and complete reimplementation of the Elf system [Pfe94].Twelf is written in Standard ML and runs under SML of New Jersey and MLWorks on Unix and Window platforms. The current version (1.2) is distributed with a complete manual, example suites, a tutorial in the form of on-line lecture notes [Pfe], and an Emacs interface. Source and binary distributions are accessible via the Twelf home page http://www.cs.cmu.edu/~twelf.