Implement threading macros and make package lib.macros to hold them.

1 files changed, 63 insertions, 0 deletions

diff --git a/lib.macros.lisp b/lib.macros.lisp
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+;;; lib.macros.lisp - 2025-02-09
+
+;; Copyright (C) 2025 Aryadev Chavali
+
+;; This program is distributed in the hope that it will be useful, but WITHOUT
+;; ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+;; FOR A PARTICULAR PURPOSE.  See the GNU General Public License Version 2 for
+;; details.
+
+;; You may distribute and modify this code under the terms of the GNU General
+;; Public License Version 2, which you should have received a copy of along with
+;; this program.  If not, please go to <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; Helpful macros for usage throughout the project.
+
+;;; Code:
+
+(in-package :lib.macros)
+
+(defmacro --> (&rest functions)
+  "Lexically bind current form as `_' for use in the next form, returning the
+  result of the last form.
+
+i.e.
+
+(--> (a1 a2...) (b1 b2...) (c1 c2...)) =
+(let* ((_ (a1 a2 ...))
+       (_ (b1 b2 ...))
+       (_ (c1 c2 ...)))
+    _ )
+
+Also includes transformer where symbols are considered unary functions i.e.
+(--> x y) <-> (--> x (y _)).
+"
+  (if (null functions)
+      nil
+      (let ((assignment-forms
+              (loop :for f :in functions
+                    :for canon-f = (if (symbolp f) (list f 'lib.macros:_) f)
+                    :collect `(lib.macros:_ ,canon-f))))
+        `(let* ,assignment-forms
+           lib.macros:_))))
+
+(defmacro ->> (&rest functions)
+  "Make current form the last argument of the next form, returning the last
+  form.
+
+i.e.
+(->> (a1 a2...) (b1 b2...) (c1 c2...)) == (c1 c2 ... (b1 b2 ... (a1 a2 ...)))
+
+Also includes transformer where fun in functions that are symbols are considered
+unary functions.
+
+Like the `|>' operator in Ocaml."
+  (if (null functions)
+      nil
+      (loop :with acc = (car functions)
+            :for func :in (cdr functions)
+            :for canon-func = (if (symbolp func) (list func) func)
+            :do (setq acc (append canon-func (list acc)))
+            :finally (return acc))))