From e5747b6c0d5751bbbcad902cc640e2ace00cd73c Mon Sep 17 00:00:00 2001
From: Jakub Jankiewicz <jcubic@onet.pl>
Date: Wed, 25 Aug 2021 11:42:09 +0200
Subject: [PATCH 1/3] recipe: add let-optional

---
 ...create-bindinng-with-optional-arguments.md | 43 +++++++++++++++++++
 www-index.scm                                 |  1 +
 2 files changed, 44 insertions(+)
 create mode 100644 recipes/create-bindinng-with-optional-arguments.md

diff --git a/recipes/create-bindinng-with-optional-arguments.md b/recipes/create-bindinng-with-optional-arguments.md
new file mode 100644
index 0000000..fb4155f
--- /dev/null
+++ b/recipes/create-bindinng-with-optional-arguments.md
@@ -0,0 +1,43 @@
+# Create binding with optionnal arguments
+
+## Problem
+
+You have a list, example from a function, and you want to simplify checking optional parameters with default values.
+
+## Solution
+
+```scheme
+(define-syntax let-optionals
+  (syntax-rules ()
+    ((_ expr ((v d) ... . tail) . body)
+     ($let-optionals (v ...) () (d ...) () f tail expr body))))
+
+(define-syntax $let-optionals
+  (syntax-rules ()
+
+    ((_ () (vt ...) _ (cl ...) f tail expr body)
+     (letrec ((f (case-lambda cl ... ((vt ... . tail) . body))))
+       (apply f expr)))
+
+    ((_ (vrf . vr*) (vt ...) (df . dr*) (cl ...) f . tailexprbody)
+     ($let-optionals vr* (vt ... vrf) dr* (cl ... ((vt ...) (f vt ... df))) f . tailexprbody))))
+```
+
+Credit [@tallflier](https://www.reddit.com/user/tallflier/)
+
+**NOTE**: this macro is requirement for base implementation of [SRFI-1](https://github.com/scheme-requests-for-implementation/srfi-1).
+
+## Usage
+
+```scheme
+(define (calc num . rest)
+  (let-optionals rest ((multipier 1) (factor 10))
+    (/ (* num multipier) factor)))
+
+(calc 10)
+;; ==> 1
+(calc 10 2)
+;; ==> 2
+(calc 10 2 5)
+;; ==> 4
+```
\ No newline at end of file
diff --git a/www-index.scm b/www-index.scm
index d710b9e..3bac713 100644
--- a/www-index.scm
+++ b/www-index.scm
@@ -1,5 +1,6 @@
 (("Pairs and lists"
   "create-k-combinations-from-list"
+  "create-bindinng-with-optional-arguments"
   "find-depth-of-list"
   "find-index-of-element-in-list"
   "find-most-frequent-element-in-list"

From 6e5921de891bd7ecf3c4f5a87655eb67b03bb016 Mon Sep 17 00:00:00 2001
From: Jakub Jankiewicz <jcubic@onet.pl>
Date: Wed, 25 Aug 2021 12:31:57 +0200
Subject: [PATCH 2/3] typo

---
 recipes/create-bindinng-with-optional-arguments.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/recipes/create-bindinng-with-optional-arguments.md b/recipes/create-bindinng-with-optional-arguments.md
index fb4155f..aad3bd2 100644
--- a/recipes/create-bindinng-with-optional-arguments.md
+++ b/recipes/create-bindinng-with-optional-arguments.md
@@ -31,8 +31,8 @@ Credit [@tallflier](https://www.reddit.com/user/tallflier/)
 
 ```scheme
 (define (calc num . rest)
-  (let-optionals rest ((multipier 1) (factor 10))
-    (/ (* num multipier) factor)))
+  (let-optionals rest ((multiplier 1) (factor 10))
+    (/ (* num multiplier) factor)))
 
 (calc 10)
 ;; ==> 1

From d6495a1be5be8d52e21c803058f3137ed33e4527 Mon Sep 17 00:00:00 2001
From: Jakub Jankiewicz <jcubic@onet.pl>
Date: Wed, 25 Aug 2021 15:43:15 +0200
Subject: [PATCH 3/3] change name and title of optional arguments recipe

---
 ...-with-optional-arguments.md => bind-optional-arguments.md} | 4 ++--
 www-index.scm                                                 | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)
 rename recipes/{create-bindinng-with-optional-arguments.md => bind-optional-arguments.md} (95%)

diff --git a/recipes/create-bindinng-with-optional-arguments.md b/recipes/bind-optional-arguments.md
similarity index 95%
rename from recipes/create-bindinng-with-optional-arguments.md
rename to recipes/bind-optional-arguments.md
index aad3bd2..d729ff0 100644
--- a/recipes/create-bindinng-with-optional-arguments.md
+++ b/recipes/bind-optional-arguments.md
@@ -1,4 +1,4 @@
-# Create binding with optionnal arguments
+# Bind optional arguments
 
 ## Problem
 
@@ -40,4 +40,4 @@ Credit [@tallflier](https://www.reddit.com/user/tallflier/)
 ;; ==> 2
 (calc 10 2 5)
 ;; ==> 4
-```
\ No newline at end of file
+```
diff --git a/www-index.scm b/www-index.scm
index 3bac713..f29f38e 100644
--- a/www-index.scm
+++ b/www-index.scm
@@ -1,6 +1,6 @@
 (("Pairs and lists"
   "create-k-combinations-from-list"
-  "create-bindinng-with-optional-arguments"
+  "bind-optional-arguments"
   "find-depth-of-list"
   "find-index-of-element-in-list"
   "find-most-frequent-element-in-list"