Merge pull request #1017 from Techcable/feature/helper-func-contains

Add `contains?` helper function to boot.janet

src/boot/boot.janet

@@ -1196,6 +1196,47 @@
   (def kw (keyword prefix (slice alias 1 -2)))
   ~(def ,alias :dyn ,;more ,kw))
 
+
+(defn contains-key?
+  ```Checks if a collection contains the specified key.
+  
+  Semantically equivalent to `(not (nil? (get collection key)))`.
+  
+  Arrays, tuples, and buffer types (string, buffer, keyword, symbol) are all indexed by integer keys.
+  For those types, this function simply checks if the index is less than the length. 
+  
+  If this function succeeds, then a call to `(in collection key)` is guarenteed
+  to succeed as well.
+  
+  Note that tables or structs (dictionaries) never contain null keys```
+  [collection key]
+  (not (nil? (get collection key))))
+
+(defn contains?
+  ```Checks if a collection contains the specified value.
+  
+  This supports any iterable type by way of the `next` function.
+  This includes buffers, dictionaries, arrays, fibers, and possibly abstract types.
+  
+  For tables and structs, this checks the values, not the keys.
+  For arrays, tuples (and any other iterable type), this simply checks if any of the values are equal.
+  
+  For buffer types (strings, buffers, keywords), this checks if the specified byte is present.
+  This is because, buffer types (strings, keywords, symbols) are simply sequences, with byte values.
+  This means they will also work with `next` and `index-of`.
+  
+  However, it also means this function will not check for substrings, only integer bytes (which could be unexpected).
+  In other words is `(contains? "foo bar" "foo")` is always false, because "foo" is not an integer byte
+  If you want to check for a substring in a buffer, then use `(truthy? (string/find substr buffer))`,
+  or just `(if (string/find substr buffer) then else)`
+  
+  In general this function has O(n) performance, since it requires iterating over all the values.
+  
+  Note that tables or structs (dictionaries) never contain null values```
+  [collection val]
+  (not (nil? (index-of val collection))))
+
+
 (defdyn *defdyn-prefix* ``Optional namespace prefix to add to keywords declared with `defdyn`.
   Use this to prevent keyword collisions between dynamic bindings.``)
 (defdyn *out* "Where normal print functions print output to.")