From 4f6622730ae10fcd414d39abb71c91348b03cc4e Mon Sep 17 00:00:00 2001
From: Ava Hahn <ava@sunnypup.io>
Date: Mon, 20 Mar 2023 21:07:16 -0700
Subject: [PATCH] added userlib reduce function

Signed-off-by: Ava Hahn <ava@sunnypup.io>
---
 Readme.org                 |  1 -
 snippets/userlib-tests.rls |  7 +++++++
 snippets/userlib.rls       | 21 +++++++++++++++++++++
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/Readme.org b/Readme.org
index e9408fa..f24e3a7 100644
--- a/Readme.org
+++ b/Readme.org
@@ -507,7 +507,6 @@ Note: this section only tracks the state of incomplete TODO items. Having everyt
 - Custom ast pretty print
 - Implement Compose for lambdas
   Document this in relevant readme sections
-- Userlib Reduce function
 - File operations
   - read-to-string
   - write-to-file
diff --git a/snippets/userlib-tests.rls b/snippets/userlib-tests.rls
index ab46c66..e2ab3bf 100644
--- a/snippets/userlib-tests.rls
+++ b/snippets/userlib-tests.rls
@@ -35,6 +35,7 @@
        (let ((test-val 0))
          (set (q test-val) 3)
          (eq? test-val 3))))
+
    ('prepend prepends to list'
      (quote
        (let ((list (2 3 4))
@@ -48,6 +49,12 @@
              (adder (lambda (x) (add 1 x))))
          (eq? (map adder list) (2 3 4)))))
 
+   ('reduce function adds numbers'
+     (quote
+       (let ((list (1 2 3))
+             (adder (lambda (x y) (add x y))))
+         (eq? (reduce adder list) (add 1 2 3)))))
+
      ;; add more test cases here
    ))
 
diff --git a/snippets/userlib.rls b/snippets/userlib.rls
index 41f9d79..0cef067 100644
--- a/snippets/userlib.rls
+++ b/snippets/userlib.rls
@@ -64,3 +64,24 @@ result is added to a new list. Returns the new list.'
       (set (q result) (cons result current-res))
       (set (q list-iter) (pop remaining))))
   result))
+
+(def reduce
+'Takes two arguments: a function and a list.
+The function is expected to take two arguments:
+* the current list item
+* the previous result
+Initially the function will take element1 and element2, outputting result1.
+Then the function will take result1 and element3, outputting result2.
+this will continue iuntil the list is exhausted.'
+(func list)
+(let ((list-iter (pop list))
+      (result (car list-iter)))
+  (set (q list-iter) (pop (cdr list-iter)))
+  (if (lt? (len list) 2)
+      (echo "list too short!")
+      (while (gt? (len list-iter) 1)
+        (let ((current (car list-iter))
+              (remaining (cdr list-iter)))
+          (set (q result) (func result current))
+          (set (q list-iter) (pop remaining)))))
+  result))