added 'arr_find', 'arr_contains' and did small fixes to 'find' and 'rfind'

stdlib/arr.sl

@@ -326,3 +326,22 @@ word dyn_arr_sorted
     dyn_arr_clone
     dyn_arr_sort
 end
+
+# arr_contains [*, addr | x] -> [* | bool]
+word arr_contains
+    over @ >r >r 8 + r> r>
+    for
+        2dup swap @ == if 1 nip nip rdrop ret end
+        swap 8 + swap
+    end 0 nip nip
+end
+
+# arr_find [*, addr | x] -> [* | bool]
+word arr_find
+    over @ >r >r 8 + r> r>
+    0 >r
+    for
+        2dup swap @ == if rswap r> nip nip rdrop ret end
+        swap 8 + swap rswap r> 1 + >r rswap
+    end rdrop -1 nip nip
+end

stdlib/utils.sl

@@ -531,7 +531,26 @@ end
 # contains [*, addr, len, addr | len] -> [* | bool]
 word contains
     2 pick for
-        4dup strcmp 1 == if 1 nip nip nip nip ret end
+        4dup strcmp 1 == if 1 nip nip nip nip rdrop ret end
         >r >r >r 1 + r> r> r>
     end 0 nip nip nip nip
 end
+
+# find the first occurence of a string inside another string, returns the index
+# find [*, addr, len, addr | len] -> [* | index]
+word find
+    0 >r 2 pick for
+        4dup strcmp 1 == if rswap r> nip nip nip nip rdrop ret end
+        >r >r >r 1 + r> r> r> rswap r> 1 + >r rswap
+    end -1 nip nip nip nip
+end
+
+# find the last occurence of a string inside another string, returns the index
+# rfind [*, addr, len, addr | len] -> [* | index]
+word rfind
+    >r >r dup >r + 1 - r> r> r>
+    2 pick 1 - >r 2 pick for
+        4dup strcmp 1 == if rswap r> nip nip nip nip rdrop ret end
+        >r >r >r 1 - r> r> r> rswap r> 1 - >r rswap
+    end -1 nip nip nip nip
+end