lib: Introduce takeEnd to get rid of some reverse . take n . reverse.

hledger-lib/Hledger/Data/Transaction.hs

@@ -302,11 +302,10 @@ commentSpace = ("  "++)
 -- appropriately bracketed/parenthesised for the given posting type.
 showAccountName :: Maybe Int -> PostingType -> AccountName -> String
 showAccountName w = fmt
-    where
-      fmt RegularPosting = take w' . T.unpack
-      fmt VirtualPosting = parenthesise . reverse . take (w'-2) . reverse . T.unpack
-      fmt BalancedVirtualPosting = bracket . reverse . take (w'-2) . reverse . T.unpack
-      w' = fromMaybe 999999 w
+  where
+    fmt RegularPosting = maybe id take w . T.unpack
+    fmt VirtualPosting = parenthesise . maybe id (takeEnd . subtract 2) w . T.unpack
+    fmt BalancedVirtualPosting = bracket . maybe id (takeEnd . subtract 2) w . T.unpack
 
 parenthesise :: String -> String
 parenthesise s = "("++s++")"

hledger-lib/Hledger/Utils/String.hs

@@ -1,6 +1,7 @@
 -- | String formatting helpers, starting to get a bit out of control.
 
 module Hledger.Utils.String (
+ takeEnd,
  -- * misc
  lowercase,
  uppercase,
@@ -57,6 +58,14 @@ import Text.Printf (printf)
 import Hledger.Utils.Parse
 import Hledger.Utils.Regex
 
+
+-- | Take elements from the end of a list.
+takeEnd n l = go (drop n l) l
+  where
+    go (_:xs) (_:ys) = go xs ys
+    go []     r      = r
+    go _      []     = []
+
 lowercase, uppercase :: String -> String
 lowercase = map toLower
 uppercase = map toUpper
@@ -86,7 +95,7 @@ stripbrackets = dropWhile (`elem` "([") . reverse . dropWhile (`elem` "])") . re
 
 elideLeft :: Int -> String -> String
 elideLeft width s =
-    if length s > width then ".." ++ reverse (take (width - 2) $ reverse s) else s
+    if length s > width then ".." ++ takeEnd (width - 2) s else s
 
 elideRight :: Int -> String -> String
 elideRight width s =