Use `stripPrefix` where appropriate.

9 files changed, 57 insertions, 54 deletions

diff --git a/src/Text/Pandoc/Readers/Docx.hs b/src/Text/Pandoc/Readers/Docx.hs
index 86ce62ced..be486c83f 100644
--- a/src/Text/Pandoc/Readers/Docx.hs
+++ b/src/Text/Pandoc/Readers/Docx.hs
@@ -86,7 +86,7 @@ import Text.Pandoc.Readers.Docx.TexChar
 import Text.Pandoc.Shared
 import Text.Pandoc.MediaBag (insertMedia, MediaBag)
 import Data.Maybe (mapMaybe, fromMaybe)
-import Data.List (delete, isPrefixOf, (\\), intercalate, intersect)
+import Data.List (delete, stripPrefix, (\\), intercalate, intersect)
 import Data.Monoid
 import qualified Data.ByteString.Lazy as B
 import qualified Data.Map as M
@@ -455,8 +455,8 @@ oMathElemToTexString (LowerLimit base limElems) = do
     --  we want to make sure to replace the `\rightarrow` with `\to`
   let arrowToTo :: String -> String
       arrowToTo "" = ""
-      arrowToTo s | "\\rightarrow" `isPrefixOf` s =
-        "\\to" ++ (arrowToTo $ drop (length "\\rightarrow") s)
+      arrowToTo s | Just s' <- stripPrefix "\\rightarrow" s =
+        "\\to" ++ arrowToTo s'
       arrowToTo (c:cs) = c : arrowToTo cs
       lim' = arrowToTo lim
   return $ case baseString of
@@ -470,8 +470,8 @@ oMathElemToTexString (UpperLimit base limElems) = do
     --  we want to make sure to replace the `\rightarrow` with `\to`
   let arrowToTo :: String -> String
       arrowToTo "" = ""
-      arrowToTo s | "\\rightarrow" `isPrefixOf` s =
-        "\\to" ++ (arrowToTo $ drop (length "\\rightarrow") s)
+      arrowToTo s | Just s' <- stripPrefix "\\rightarrow" s =
+        "\\to" ++ arrowToTo s'
       arrowToTo (c:cs) = c : arrowToTo cs
       lim' = arrowToTo lim
   return $ case baseString of
@@ -698,8 +698,8 @@ ilToCode Space = " "
 ilToCode _     = ""
 
 isHeaderClass :: String -> Maybe Int
-isHeaderClass s | "Heading" `isPrefixOf` s =
-  case reads (drop (length "Heading") s) :: [(Int, String)] of
+isHeaderClass s | Just s' <- stripPrefix "Heading" s =
+  case reads s' :: [(Int, String)] of
     [] -> Nothing
     ((n, "") : []) -> Just n
     _       -> Nothing
diff --git a/src/Text/Pandoc/Shared.hs b/src/Text/Pandoc/Shared.hs
index f0e5bbe5d..93a575809 100644
--- a/src/Text/Pandoc/Shared.hs
+++ b/src/Text/Pandoc/Shared.hs
@@ -99,7 +99,7 @@ import System.Environment (getProgName)
 import System.Exit (exitWith, ExitCode(..))
 import Data.Char ( toLower, isLower, isUpper, isAlpha,
                    isLetter, isDigit, isSpace )
-import Data.List ( find, isPrefixOf, intercalate )
+import Data.List ( find, stripPrefix, intercalate )
 import qualified Data.Map as M
 import Network.URI ( escapeURIString, isURI, nonStrictRelativeTo,
                      unEscapeString, parseURIReference, isAllowedInURI )
@@ -183,9 +183,9 @@ substitute :: (Eq a) => [a] -> [a] -> [a] -> [a]
 substitute _ _ [] = []
 substitute [] _ xs = xs
 substitute target replacement lst@(x:xs) =
-    if target `isPrefixOf` lst
-       then replacement ++ substitute target replacement (drop (length target) lst)
-       else x : substitute target replacement xs
+    case stripPrefix target lst of
+      Just lst' -> replacement ++ substitute target replacement lst'
+      Nothing   -> x : substitute target replacement xs
 
 ordNub :: (Ord a) => [a] -> [a]
 ordNub l = go Set.empty l
@@ -808,9 +808,9 @@ fetchItem' media sourceURL s = do
 -- | Read from a URL and return raw data and maybe mime type.
 openURL :: String -> IO (Either E.SomeException (BS.ByteString, Maybe String))
 openURL u
-  | "data:" `isPrefixOf` u =
-    let mime     = takeWhile (/=',') $ drop 5 u
-        contents = B8.pack $ unEscapeString $ drop 1 $ dropWhile (/=',') u
+  | Just u' <- stripPrefix "data:" u =
+    let mime     = takeWhile (/=',') u'
+        contents = B8.pack $ unEscapeString $ drop 1 $ dropWhile (/=',') u'
     in  return $ Right (decodeLenient contents, Just mime)
 #ifdef HTTP_CLIENT
   | otherwise = withSocketsDo $ E.try $ do
diff --git a/src/Text/Pandoc/Writers/AsciiDoc.hs b/src/Text/Pandoc/Writers/AsciiDoc.hs
index ffcce7990..e5b8c5167 100644
--- a/src/Text/Pandoc/Writers/AsciiDoc.hs
+++ b/src/Text/Pandoc/Writers/AsciiDoc.hs
@@ -43,7 +43,8 @@ import Text.Pandoc.Shared
 import Text.Pandoc.Writers.Shared
 import Text.Pandoc.Options
 import Text.Pandoc.Parsing hiding (blankline, space)
-import Data.List ( isPrefixOf, intersperse, intercalate )
+import Data.Maybe (fromMaybe)
+import Data.List ( stripPrefix, intersperse, intercalate )
 import Text.Pandoc.Pretty
 import Control.Monad.State
 import qualified Data.Map as M
@@ -401,7 +402,7 @@ inlineToAsciiDoc opts (Link txt (src, _tit)) = do
   let prefix = if isRelative
                   then text "link:"
                   else empty
-  let srcSuffix = if isPrefixOf "mailto:" src then drop 7 src else src
+  let srcSuffix = fromMaybe src (stripPrefix "mailto:" src)
   let useAuto = case txt of
                       [Str s] | escapeURI s == srcSuffix -> True
                       _                                  -> False
diff --git a/src/Text/Pandoc/Writers/Docbook.hs b/src/Text/Pandoc/Writers/Docbook.hs
index 25c1e156e..bc4732d7f 100644
--- a/src/Text/Pandoc/Writers/Docbook.hs
+++ b/src/Text/Pandoc/Writers/Docbook.hs
@@ -37,7 +37,7 @@ import Text.Pandoc.Writers.Shared
 import Text.Pandoc.Options
 import Text.Pandoc.Templates (renderTemplate')
 import Text.Pandoc.Readers.TeXMath
-import Data.List ( isPrefixOf, intercalate, isSuffixOf )
+import Data.List ( stripPrefix, isPrefixOf, intercalate, isSuffixOf )
 import Data.Char ( toLower )
 import Data.Monoid ( Any(..) )
 import Text.Pandoc.Highlighting ( languages, languagesByExtension )
@@ -312,19 +312,19 @@ inlineToDocbook _ (RawInline f x) | f == "html" || f == "docbook" = text x
                                   | otherwise                     = empty
 inlineToDocbook _ LineBreak = text "\n"
 inlineToDocbook _ Space = space
-inlineToDocbook opts (Link txt (src, _)) =
-  if isPrefixOf "mailto:" src
-     then let src' = drop 7 src
-              emailLink = inTagsSimple "email" $ text $
-                          escapeStringForXML $ src'
-          in  case txt of
-               [Str s] | escapeURI s == src' -> emailLink
-               _             -> inlinesToDocbook opts txt <+>
-                                  char '(' <> emailLink <> char ')'
-     else (if isPrefixOf "#" src
-              then inTags False "link" [("linkend", drop 1 src)]
-              else inTags False "ulink" [("url", src)]) $
-          inlinesToDocbook opts txt
+inlineToDocbook opts (Link txt (src, _))
+  | Just email <- stripPrefix "mailto:" src =
+      let emailLink = inTagsSimple "email" $ text $
+                      escapeStringForXML $ email
+      in  case txt of
+           [Str s] | escapeURI s == email -> emailLink
+           _             -> inlinesToDocbook opts txt <+>
+                              char '(' <> emailLink <> char ')'
+  | otherwise =
+      (if isPrefixOf "#" src
+            then inTags False "link" [("linkend", drop 1 src)]
+            else inTags False "ulink" [("url", src)]) $
+        inlinesToDocbook opts txt
 inlineToDocbook _ (Image _ (src, tit)) =
   let titleDoc = if null tit
                    then empty
diff --git a/src/Text/Pandoc/Writers/FB2.hs b/src/Text/Pandoc/Writers/FB2.hs
index 7a9bff4fe..930076c9e 100644
--- a/src/Text/Pandoc/Writers/FB2.hs
+++ b/src/Text/Pandoc/Writers/FB2.hs
@@ -29,7 +29,7 @@ import Control.Monad.State (StateT, evalStateT, get, modify)
 import Control.Monad.State (liftM, liftM2, liftIO)
 import Data.ByteString.Base64 (encode)
 import Data.Char (toLower, isSpace, isAscii, isControl)
-import Data.List (intersperse, intercalate, isPrefixOf)
+import Data.List (intersperse, intercalate, isPrefixOf, stripPrefix)
 import Data.Either (lefts, rights)
 import Network.Browser (browse, request, setAllowRedirects, setOutHandler)
 import Network.HTTP (catchIO_, getRequest, getHeaders, getResponseBody)
@@ -252,22 +252,21 @@ readDataURI :: String -- ^ URI
             -> Maybe (String,String,Bool,String)
                -- ^ Maybe (mime,charset,isBase64,data)
 readDataURI uri =
-    let prefix = "data:"
-    in  if not (prefix `isPrefixOf` uri)
-        then Nothing
-        else
-            let rest = drop (length prefix) uri
-                meta = takeWhile (/= ',') rest  -- without trailing ','
-                uridata = drop (length meta + 1) rest
-                parts = split (== ';') meta
-                (mime,cs,enc)=foldr upd ("text/plain","US-ASCII",False) parts
-            in  Just (mime,cs,enc,uridata)
+  case stripPrefix "data:" uri of
+    Nothing   -> Nothing
+    Just rest ->
+      let meta = takeWhile (/= ',') rest  -- without trailing ','
+          uridata = drop (length meta + 1) rest
+          parts = split (== ';') meta
+          (mime,cs,enc)=foldr upd ("text/plain","US-ASCII",False) parts
+      in  Just (mime,cs,enc,uridata)
+
  where
    upd str m@(mime,cs,enc)
-       | isMimeType str               = (str,cs,enc)
-       | "charset=" `isPrefixOf` str  = (mime,drop (length "charset=") str,enc)
-       | str ==  "base64"             = (mime,cs,True)
-       | otherwise                    = m
+       | isMimeType str                          = (str,cs,enc)
+       | Just str' <- stripPrefix "charset=" str = (mime,str',enc)
+       | str ==  "base64"                        = (mime,cs,True)
+       | otherwise                               = m
 
 -- Without parameters like ;charset=...; see RFC 2045, 5.1
 isMimeType :: String -> Bool
diff --git a/src/Text/Pandoc/Writers/LaTeX.hs b/src/Text/Pandoc/Writers/LaTeX.hs
index ea704c91d..3ea070ee7 100644
--- a/src/Text/Pandoc/Writers/LaTeX.hs
+++ b/src/Text/Pandoc/Writers/LaTeX.hs
@@ -37,7 +37,7 @@ import Text.Pandoc.Options
 import Text.Pandoc.Templates
 import Text.Printf ( printf )
 import Network.URI ( isURI, unEscapeString )
-import Data.List ( (\\), isSuffixOf, isInfixOf,
+import Data.List ( (\\), isSuffixOf, isInfixOf, stripPrefix,
                    isPrefixOf, intercalate, intersperse )
 import Data.Char ( toLower, isPunctuation, isAscii, isLetter, isDigit, ord )
 import Data.Maybe ( fromMaybe )
@@ -761,8 +761,8 @@ inlineToLaTeX (Link txt (src, _)) =
              do modify $ \s -> s{ stUrl = True }
                 src' <- stringToLaTeX URLString src
                 return $ text $ "\\url{" ++ src' ++ "}"
-        [Str x] | "mailto:" `isPrefixOf` src &&
-                  escapeURI x == drop 7 src -> -- email autolink
+        [Str x] | Just rest <- stripPrefix "mailto:" src,
+                  escapeURI x == rest -> -- email autolink
              do modify $ \s -> s{ stUrl = True }
                 src' <- stringToLaTeX URLString src
                 contents <- inlineListToLaTeX txt
diff --git a/src/Text/Pandoc/Writers/Man.hs b/src/Text/Pandoc/Writers/Man.hs
index 2af7c0e31..6b2c4c200 100644
--- a/src/Text/Pandoc/Writers/Man.hs
+++ b/src/Text/Pandoc/Writers/Man.hs
@@ -36,7 +36,8 @@ import Text.Pandoc.Writers.Shared
 import Text.Pandoc.Options
 import Text.Pandoc.Readers.TeXMath
 import Text.Printf ( printf )
-import Data.List ( isPrefixOf, intersperse, intercalate )
+import Data.List ( stripPrefix, intersperse, intercalate )
+import Data.Maybe (fromMaybe)
 import Text.Pandoc.Pretty
 import Text.Pandoc.Builder (deleteMeta)
 import Control.Monad.State
@@ -343,7 +344,7 @@ inlineToMan _ (LineBreak) = return $
 inlineToMan _ Space = return space
 inlineToMan opts (Link txt (src, _)) = do
   linktext <- inlineListToMan opts txt
-  let srcSuffix = if isPrefixOf "mailto:" src then drop 7 src else src
+  let srcSuffix = fromMaybe src (stripPrefix "mailto:" src)
   return $ case txt of
            [Str s]
              | escapeURI s == srcSuffix ->
diff --git a/src/Text/Pandoc/Writers/Markdown.hs b/src/Text/Pandoc/Writers/Markdown.hs
index a859267cc..211d793dd 100644
--- a/src/Text/Pandoc/Writers/Markdown.hs
+++ b/src/Text/Pandoc/Writers/Markdown.hs
@@ -38,7 +38,8 @@ import Text.Pandoc.Shared
 import Text.Pandoc.Writers.Shared
 import Text.Pandoc.Options
 import Text.Pandoc.Parsing hiding (blankline, blanklines, char, space)
-import Data.List ( group, isPrefixOf, find, intersperse, transpose, sortBy )
+import Data.Maybe (fromMaybe)
+import Data.List ( group, stripPrefix, find, intersperse, transpose, sortBy )
 import Data.Char ( isSpace, isPunctuation )
 import Data.Ord ( comparing )
 import Text.Pandoc.Pretty
@@ -815,7 +816,7 @@ inlineToMarkdown opts (Link txt (src, tit)) = do
   let linktitle = if null tit
                      then empty
                      else text $ " \"" ++ tit ++ "\""
-  let srcSuffix = if isPrefixOf "mailto:" src then drop 7 src else src
+  let srcSuffix = fromMaybe src (stripPrefix "mailto:" src)
   let useAuto = isURI src &&
                 case txt of
                       [Str s] | escapeURI s == srcSuffix -> True
diff --git a/src/Text/Pandoc/Writers/RST.hs b/src/Text/Pandoc/Writers/RST.hs
index 5e97d2ac3..57ebfc360 100644
--- a/src/Text/Pandoc/Writers/RST.hs
+++ b/src/Text/Pandoc/Writers/RST.hs
@@ -37,7 +37,8 @@ import Text.Pandoc.Shared
 import Text.Pandoc.Writers.Shared
 import Text.Pandoc.Templates (renderTemplate')
 import Text.Pandoc.Builder (deleteMeta)
-import Data.List ( isPrefixOf, intersperse, transpose )
+import Data.Maybe (fromMaybe)
+import Data.List ( isPrefixOf, stripPrefix, intersperse, transpose )
 import Network.URI (isURI)
 import Text.Pandoc.Pretty
 import Control.Monad.State
@@ -401,7 +402,7 @@ inlineToRST (Link [Str str] (src, _))
     if "mailto:" `isPrefixOf` src
        then src == escapeURI ("mailto:" ++ str)
        else src == escapeURI str = do
-  let srcSuffix = if isPrefixOf "mailto:" src then drop 7 src else src
+  let srcSuffix = fromMaybe src (stripPrefix "mailto:" src)
   return $ text srcSuffix
 inlineToRST (Link [Image alt (imgsrc,imgtit)] (src, _tit)) = do
   label <- registerImage alt (imgsrc,imgtit) (Just src)