hylang/hy 0.15.0 on GitHub

Removals

Dotted lists, HyCons, cons, cons?, and list* have been removed. These were redundant with Python's built-in data structures and Hy's most common model types (HyExpression, HyList, etc.).
&key is no longer special in lambda lists. Use &optional instead.
Lambda lists can no longer unpack tuples.
ap-pipe and ap-compose have been removed. Use threading macros and comp instead.
for/a has been removed. Use (for [:async ...] ...) instead.
(except) is no longer allowed. Use (except []) instead.
(import [foo]) is no longer allowed. Use (import foo) instead.

HyExpression, HyDict, and HySet no longer inherit from HyList. This means you can no longer use alternative punctuation in place of square brackets in special forms (e.g. (fn (x) ...) instead of the standard (fn [x] ...)).
Mangling rules have been overhauled; now, mangled names are always legal Python identifiers.
_ and - are now equivalent, even as single-character names.
- The REPL history variable _ is now *1.
Non-shadow unary =, is, <, etc. now evaluate their argument instead of ignoring it.
list-comp, set-comp, dict-comp, and genexpr have been replaced by lfor, sfor, dfor, and gfor, respectively, which use a new syntax and have additional features. All Python comprehensions can now be written in Hy.
&-parameters in lambda lists must now appear in the same order that Python expects.
Literal keywords now evaluate to themselves, and HyKeyword no longer inherits from a Python string type
HySymbol no longer inherits from HyString.

Python 3.7 is now supported.
while and for are allowed to have empty bodies.
for supports the various new clause types offered by lfor.
defclass in Python 3 supports specifying metaclasses and other keyword arguments.
Added mangle and unmangle as core functions.
Added more REPL history variables: *2 and *3.
Added a REPL variable holding the last exception: *e.
Added a command-line option -E per CPython.
Added a new module hy.model_patterns.

hy2py should now output legal Python code equivalent to the input Hy code in all cases.
Fixed (return) so it can exit a Python 2 generator.
Fixed a case where -> and ->> duplicated an argument.
Fixed bugs that caused defclass to drop statements or crash.
Fixed a REPL crash caused by illegal backslash escapes.
NaN can no longer create an infinite loop during macro-expansion.
Fixed a bug that caused try to drop expressions.
The compiler now properly recognizes unquote-splice.
Trying to import a dotted name is now a syntax error, as in Python.
defmacro! now allows optional arguments.
Fixed handling of variables that are bound multiple times in a single let.