1. General purpose language syntactically like RATFOR, semantically like C. Lacks structures and pointers. Used as a source language for Jack W. Davidson and Christopher W. Fraser's peephole optimiser which inspired GCC RTL and other optimisation ideas.
ftp://ftp.cs.princeton.edu/pub/y+po.tar.Z. It is a copy of the original distribution from the University of Arizona during the early 80's, totally unsupported.
["The Y Programming Language", D.R. Hanson, SIGPLAN Notices 16(2):59-68 (Feb 1981)].
[Jack W. Davidson and Christopher W. Fraser, "The Design and Application of a Retargetable Peephole Optimiser", TOPLAS, Apr. 1980].
[Jack W. Davidson, "Simplifying Code Through Peephole Optimisation" Technical Report TR81-19, The University of Arizona, Tucson, AZ, 1981].
[Jack W. Davidson and Christopher W. Fraser, "Register Allocation and Exhaustive Peephole Optimisation" Software-Practice and Experience, Sep. 1984].
2. See fixed point combinator.