From The Free On-line Dictionary of Computing (19 January 2023):
Y
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.