Add drop-while

docs/api/nfnl/core.md

@@ -13,6 +13,7 @@
 - [`count`](#count)
 - [`dec`](#dec)
 - [`distinct`](#distinct)
+- [`drop-while`](#drop-while)
 - [`empty?`](#empty)
 - [`even?`](#even)
 - [`filter`](#filter)
@@ -164,6 +165,15 @@ Function signature:
 
 Takes a sequential table of values (xs) and returns a distinct sequential table with all duplicates removed.
 
+## `drop-while`
+Function signature:
+
+```
+(drop-while f xs)
+```
+
+Drop values while (f x) returns true.
+
 ## `empty?`
 Function signature:
 

fnl/nfnl/core.fnl

@@ -441,6 +441,19 @@
           (set done? true))))
     acc))
 
+(fn drop-while [f xs]
+  "Drop values while (f x) returns true."
+  (local xs (seq xs))
+  (when xs
+    (var acc [])
+    (var done? false)
+    (for [i 1 (count xs) 1]
+      (let [v (. xs i)]
+        (when (or done? (not (f v)))
+          (table.insert acc v)
+          (set done? true))))
+    acc))
+
 {: rand
  : nil?
  : number?
@@ -494,4 +507,5 @@
  : clear-table!
  : sequential?
  : seq
- : take-while}
+ : take-while
+ : drop-while}

fnl/spec/nfnl/core_spec.fnl

@@ -512,3 +512,14 @@
             [[:hi :world]]
             (core.take-while #(= (. $1 1) :hi) {:hi :world}))
           nil))))
+
+(describe
+  "drop-while"
+  (fn []
+    (it "drops values while f is true"
+        (fn []
+          (assert.are.same [1 2 3] (core.drop-while #(< $1 0) [-1 -2 -3 1 2 3]))
+          (assert.are.same [2 3] (core.drop-while #(< $1 2) [1 2 3]))
+          (assert.are.same nil (core.drop-while #(> $1 0) nil))
+          (assert.are.same [] (core.drop-while #(= (. $1 1) :hi) {:hi :world}))
+          nil))))