From bbde84c7d7d525f8fcfa3638ae0bca428efc9e67 Mon Sep 17 00:00:00 2001
From: Aryadev Chavali <aryadev@aryadevchavali.com>
Date: Sun, 9 Feb 2025 13:29:22 +0000
Subject: Add type alias for function and macro for defining functions with
 type specifier

`fn' is a convenience macro for defining functions with a type
specifier.  Only really matters for `sbcl` and other hard-optimising
Lisp interpreters which actually take these seriously.
---
 lib.macros.lisp | 12 ++++++++++++
 packages.lisp   |  3 ++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/lib.macros.lisp b/lib.macros.lisp
index f96636d..057a89f 100644
--- a/lib.macros.lisp
+++ b/lib.macros.lisp
@@ -66,3 +66,15 @@ Like the `|>' operator in Ocaml."
   `(loop :while ,condition
          :do
          (progn ,@body)))
+
+(deftype -> (args result)
+  "Type alias for function."
+  `(function ,args ,result))
+
+(defmacro fn (name lambda-list type &body body)
+  "Construct a function `NAME' with a declared function type `TYPE' that takes
+arguments `LAMBDA-LIST' with body `BODY'."
+  `(progn
+     (declaim (ftype ,type ,name))
+     (defun ,name ,lambda-list
+       ,@body)))
diff --git a/packages.lisp b/packages.lisp
index 8e66c78..f7e56a6 100644
--- a/packages.lisp
+++ b/packages.lisp
@@ -21,7 +21,8 @@
   (:use :cl)
   (:export
    :_ :--> :->>
-   :while))
+   :while
+   :-> :fn))
 
 (defpackage main
   (:use :cl :lib.macros)
-- 
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