Hy (programming language)

Hy is a dialect of the Lisp programming language designed to interact with Python by translating s-expressions into Python's abstract syntax tree (AST).^[2][3] Hy was introduced at Python Conference (PyCon) 2013 by Paul Tagliamonte.^[4] Lisp allows operating on code as data (metaprogramming), thus Hy can be used to write domain-specific languages.^[5]

Hy

Hy logo – Cuddles the cuttlefish
Paradigm	Multi-paradigm: procedural, functional, object-oriented, meta, reflective, generic
Family	Lisp
Designed by	Paul Tagliamonte
Developers	Core team
First appeared	2013; 12 years ago (2013)
Stable release	1.1.0[1]  / 8 May 2025; 17 days ago (8 May 2025)
Scope	lexical, optionally dynamic[citation needed]
Platform	IA-32, x86-64
OS	Cross-platform
License	MIT-style
Filename extensions	.hy
Website	hylang.org
Influenced by
Kawa, Clojure, Common Lisp

Similar to Kawa's and Clojure's mappings onto the Java virtual machine (JVM),^[6][7] Hy is meant to operate as a transparent Lisp front-end for Python.^[8] It allows Python libraries, including the standard library, to be imported and accessed alongside Hy code with a compiling^{[note 1]} step where both languages are converted into Python's AST.^{[note 2][9][10][11]}

Example code

From the language documentation:^[12]

=> (print "Hy!")
Hy!
=> (defn salutationsnm [name] (print (+ "Hy " name "!")))
=> (salutationsnm "YourName")
Hy YourName!

See also

• Common Lisp
• Clojure
• Kawa (Scheme implementation)
• CLPython

Notes

1. The term "compiled" may apply to expressing Hy code in Python's AST or converting that AST into bytecode, the latter being dependent on the specific Python interpreter used and not Hy.
2. Hy is tested on Python 2.7, 3.4 through 3.6, and PyPy.