Avoid 'iff' for clarity

Instead write it in full as 'if and only if'.

Author: AlistairB

src/Data/Text.hs

@@ -1042,7 +1042,7 @@ minimum t = S.minimum (stream t)
 -- __Properties__
 --
 -- @'head' ('scanl' f z xs) = z@
--- 
+--
 -- @'last' ('scanl' f z xs) = 'foldl' f z xs@
 scanl :: (Char -> Char -> Char) -> Char -> Text -> Text
 scanl f z t = unstream (S.scanl g z (stream t))
@@ -1848,14 +1848,14 @@ unwords = intercalate (singleton ' ')
 {-# INLINE unwords #-}
 
 -- | /O(n)/ The 'isPrefixOf' function takes two 'Text's and returns
--- 'True' iff the first is a prefix of the second.
+-- 'True' if and only if the first is a prefix of the second.
 isPrefixOf :: Text -> Text -> Bool
 isPrefixOf a@(Text _ _ alen) b@(Text _ _ blen) =
     alen <= blen && S.isPrefixOf (stream a) (stream b)
 {-# INLINE [1] isPrefixOf #-}
 
 -- | /O(n)/ The 'isSuffixOf' function takes two 'Text's and returns
--- 'True' iff the first is a suffix of the second.
+-- 'True' if and only if the first is a suffix of the second.
 isSuffixOf :: Text -> Text -> Bool
 isSuffixOf a@(Text _aarr _aoff alen) b@(Text barr boff blen) =
     d >= 0 && a == b'
@@ -1865,7 +1865,7 @@ isSuffixOf a@(Text _aarr _aoff alen) b@(Text barr boff blen) =
 {-# INLINE isSuffixOf #-}
 
 -- | /O(n+m)/ The 'isInfixOf' function takes two 'Text's and returns
--- 'True' iff the first is contained, wholly and intact, anywhere
+-- 'True' if and only if the first is contained, wholly and intact, anywhere
 -- within the second.
 --
 -- In (unlikely) bad cases, this function's time complexity degrades

src/Data/Text/Internal/Fusion/Common.hs

@@ -834,7 +834,7 @@ minimum (Stream next0 s0 _len) = loop0_minimum s0
 -- __Properties__
 --
 -- @'head' ('scanl' f z xs) = z@
--- 
+--
 -- @'last' ('scanl' f z xs) = 'foldl' f z xs@
 scanl :: (Char -> Char -> Char) -> Char -> Stream Char -> Stream Char
 scanl f z0 (Stream next0 s0 len) = Stream next (Scan1 z0 s0) (len+1) -- HINT maybe too low
@@ -1008,7 +1008,7 @@ dropWhile p (Stream next0 s0 len) = Stream next (L s0) (len - unknownSize)
 {-# INLINE [0] dropWhile #-}
 
 -- | /O(n)/ The 'isPrefixOf' function takes two 'Stream's and returns
--- 'True' iff the first is a prefix of the second.
+-- 'True' if and only if the first is a prefix of the second.
 --
 -- __Properties__
 --

src/Data/Text/Lazy.hs

@@ -1460,7 +1460,7 @@ unwords = intercalate (singleton ' ')
 {-# INLINE unwords #-}
 
 -- | /O(n)/ The 'isPrefixOf' function takes two 'Text's and returns
--- 'True' iff the first is a prefix of the second.
+-- 'True' if and only if the first is a prefix of the second.
 isPrefixOf :: Text -> Text -> Bool
 isPrefixOf Empty _  = True
 isPrefixOf _ Empty  = False
@@ -1474,14 +1474,14 @@ isPrefixOf (Chunk x xs) (Chunk y ys)
         ly = T.length y
 
 -- | /O(n)/ The 'isSuffixOf' function takes two 'Text's and returns
--- 'True' iff the first is a suffix of the second.
+-- 'True' if and only if the first is a suffix of the second.
 isSuffixOf :: Text -> Text -> Bool
 isSuffixOf x y = reverse x `isPrefixOf` reverse y
 {-# INLINE isSuffixOf #-}
 -- TODO: a better implementation
 
 -- | /O(n+m)/ The 'isInfixOf' function takes two 'Text's and returns
--- 'True' iff the first is contained, wholly and intact, anywhere
+-- 'True' if and only if the first is contained, wholly and intact, anywhere
 -- within the second.
 --
 -- This function is strict in its first argument, and lazy in its