Macros

LisPy's macro system is highly inspired by Clojure's macro system. You can check out the Chapter 7 and Chapter 8 of "Brave Clojure" for more information about Clojure's macro system.

Expression Nodes

These nodes are defined in src/lispython/core/nodes.py.

You can check out how to manipulate these nodes in

• the definitions of nodes themselves
• the definitions of built-in macros in src/lispython/macros/sugar.lpy.

quote

'expr

syntax-quote

`expr

unquote

~expr

unquote-splicing

~@expr

Macro Definition

Just change def in function definition to defmacro. And macros usually return a quoted expression.

(defmacro name [args*]
  body*)

Macro Example

(defmacro when [pred *body]
  (return `(if ~pred
             (do ~@body))))

(defmacro cond [*body]
  (def recur [*body]
    (if (< (len body) 4)
        (return `(if ~@body))
        (do (= [test then *orelse] body)
            (return `(if ~test ~then ~(recur *orelse))))))
  (return (recur *body)))

(defmacro -> [x *fs]
  (if (== 0 (len fs))
      (return x))
  (= [f *rest] fs)
  (if (isinstance f Paren)
      (do (f.list.insert 1 x)
          (return `(-> ~f ~@rest)))
      (return `(-> (~f ~x) ~@rest))))

You can find more in src/lispython/macros/sugar.lpy.