From b29855047be9a172d570db71600425b2b06a8a59 Mon Sep 17 00:00:00 2001
From: Aryadev Chavali <aryadev@aryadevchavali.com>
Date: Mon, 10 Feb 2025 07:14:05 +0000
Subject: Implement `$` operator, second class version of the applicative
 operator

The `$` operator takes a sequence of FORMS and returns a unary
function which applies the input through that sequence via the `->>`
operator.

For example, consider the predicate "not null".  `null` is built into
Common Lisp but "not null" requires writing a
function (lambda (x) (not (null x))).  Now, using this operator, you
can write ($ not null) which returns the same lambda as above while
being more concise.
---
 lib.macros.lisp | 6 ++++++
 packages.lisp   | 3 ++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/lib.macros.lisp b/lib.macros.lisp
index 5489564..f02e7a2 100644
--- a/lib.macros.lisp
+++ b/lib.macros.lisp
@@ -77,3 +77,9 @@ arguments `LAMBDA-LIST' with body `BODY'."
      (declaim (ftype ,type ,name))
      (defun ,name ,lambda-list
        ,@body)))
+
+(defmacro $ (&rest forms)
+  "Given a sequence of FORMS, return a unary function which applies each form
+sequentially"
+  `(lambda (x)
+     (->> x ,@forms)))
diff --git a/packages.lisp b/packages.lisp
index aff5b68..d50945b 100644
--- a/packages.lisp
+++ b/packages.lisp
@@ -22,7 +22,8 @@
   (:export
    :_ :--> :->>
    :while
-   :-> :fn))
+   :-> :fn
+   :$))
 
 (defpackage lib.functions
   (:use :cl :lib.macros)
-- 
cgit v1.2.3-13-gbd6f