From f83f3ea71a897428902d78b217b207b62e7ad8d2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Thu, 14 May 2020 11:01:44 +0200
Subject: Add label macro.

---
 module/util.scm | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

(limited to 'module/util.scm')

diff --git a/module/util.scm b/module/util.scm
index 0417d36f..10e36d4e 100644
--- a/module/util.scm
+++ b/module/util.scm
@@ -14,7 +14,7 @@
                 -> ->> set set-> aif awhen
                 tree-map let-lazy let-env
                 case* define-many
-                and=>>
+                and=>> label
                 print-and-return
                 )
   #:replace (let* set! define-syntax
@@ -256,6 +256,23 @@
      (begin (def symbols value) ...
             (define-many def rest ...))]))
 
+;; Attach a label to a function, allowing it to call itself
+;; without actually giving it a name (can also be thought
+;; of as letrec-1).
+;; @example
+;; ((label fact
+;;   (match-lambda
+;;     [0 1]
+;;     [x (* x (fact (1- x)))]))
+;;  5)
+;; @end example
+(define-syntax label
+  (syntax-rules ()
+    [(_ self proc)
+     (letrec ((self proc))
+       proc)]))
+
+
 ;; This function borrowed from web-ics (calendar util)
 (define* (sort* items comperator #:optional (get identity))
   "A sort function more in line with how python's sorted works"
-- 
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