roam/20210608234049-hy.org

:PROPERTIES:
:ID:       295a5f40-5639-45e0-b277-8b5aecee600c
:END:
#+title: Hy

A lisp dialect of Python.

* Example
#+name: dataclass
#+begin_src hy :exports code :eval never
  (import [dataclasses [dataclass])

  (with-decorator dataclass
    (defclass Thing []
      (^str name)
      (^int age)))
#+end_src

Disassembling the above code generates the following Python equivalent.

#+begin_src hy :exports results :cache yes :wrap src python
  (disassemble
    (quote
      (do
        (import [dataclasses [dataclass]])

        (with-decorator dataclass
          (defclass Thing []
            (^str description)
            (^int value)))))
    True)
#+end_src

#+RESULTS[08e5153ad26dcf0fd8ca2a7c041eb26268461381]:
#+begin_src python
from dataclasses import dataclass


@dataclass
class Thing:
    description: str
    value: int
#+end_src

* Annotations
Supports [[id:5cb1f706-0162-4e6d-9cd8-dc6af3ae68cc][Python Typing]] annotations via the special form =^=:

#+begin_src hy :exports code :eval never
  ; Annotate the variable x as an int (equivalent to `x: int`).
  (^int x)
  ; Can annotate with expressions if needed (equivalent to `y: f(x)`).
  (^(f x) y)

  ; Annotations with an assignment: each annotation (int, str) covers the term that
  ; immediately follows.
  ; Equivalent to: x: int = 1; y = 2; z: str = 3
  (setv ^int x 1 y 2 ^str z 3)

  ; Annotate a as an int, c as an int, and b as a str.
  ; Equivalent to: def func(a: int, b: str = None, c: int = 1): ...
  (defn func [^int a ^str [b None] ^int [c 1]] ...)
#+end_src