Text: flip isSubsequenceOf

Previous argument order was alike `lookup` argument order mistake, when key
cached (compiler saturates function) across DBs.

Efficient use of the function is to all it once (per pattern) on the whole
contents.

So the contents should be cached first, and the search patterns are switchable.

Author: Anton-Latukha

src/Data/Text.hs

@@ -1879,20 +1879,20 @@ isInfixOf needle haystack
 {-# INLINE [1] isInfixOf #-}
 
 -- | The 'isSubsequenceOf' function takes two 'Text's and returns
--- 'True' iff the first is a subsequence of a second.
--- (characters of the first argument appear in same sequential order in
--- the second, to say if first argument that can be derived by deleting some
--- or no elements from the second).
+-- 'True' iff the second is a subsequence of the first.
+-- (characters of the second argument appear in same sequential order in
+-- the first, to say if second argument can be derived by deleting some
+-- or no elements from the first).
 isSubsequenceOf :: Text -> Text -> Bool
-isSubsequenceOf sf tf
+isSubsequenceOf tf sf
   | length sf > length tf = False
-  | otherwise = subseqOf sf tf
+  | otherwise = subseqOf tf sf
  where
-  subseqOf s t
+  subseqOf t s
     | null s = True
     | null t = False
-    | unsafeHead s == unsafeHead t = subseqOf (unsafeTail s) (unsafeTail t)
-    | otherwise = subseqOf s $ unsafeTail t
+    | unsafeHead s == unsafeHead t = subseqOf (unsafeTail t) (unsafeTail s)
+    | otherwise = subseqOf (unsafeTail t) s
 
 -------------------------------------------------------------------------------
 -- * View patterns