Only display horizontal lines if there are non-empty separators

src/Text/Layout/Table.hs

@@ -232,7 +232,7 @@ tableLines :: Cell a
            -> [RowGroup a] -- ^ Rows which form a cell together
            -> [String]
 tableLines specs TableStyle { .. } header rowGroups =
-    topLine : addHeaderLines (rowGroupLines ++ [bottomLine])
+    maybe id (:) optTopLine . addHeaderLines $ maybe id (\b -> (++[b])) optBottomLine rowGroupLines
   where
     -- Helpers for horizontal lines that will put layout characters arround and
     -- in between a row of the pre-formatted grid.
@@ -246,27 +246,28 @@ tableLines specs TableStyle { .. } header rowGroups =
         (sym', l) = let l' = length sym in if l' == 0 then (" ", 1) else (sym, l')
 
     -- Horizontal seperator lines that occur in a table.
-    topLine       = hLineDetail realTopH realTopL realTopC realTopR $ fakeColumns realTopH
-    bottomLine    = hLineDetail groupBottomH groupBottomL groupBottomC groupBottomR $ fakeColumns groupBottomH
-    groupSepLine  = hLineDetail groupSepH groupSepLC groupSepC groupSepRC $ fakeColumns groupSepH
-    headerSepLine = hLineDetail headerSepH headerSepLC headerSepC headerSepRC $ fakeColumns headerSepH
+    optTopLine       = optHorizontalDetailLine realTopH realTopL realTopC realTopR $ fakeColumns realTopH
+    optBottomLine    = optHorizontalDetailLine groupBottomH groupBottomL groupBottomC groupBottomR $ fakeColumns groupBottomH
+    optGroupSepLine  = optHorizontalDetailLine groupSepH groupSepLC groupSepC groupSepRC $ fakeColumns groupSepH
+    optHeaderSepLine = optHorizontalDetailLine headerSepH headerSepLC headerSepC headerSepRC $ fakeColumns headerSepH
 
     -- Vertical content lines
-    rowGroupLines =
-        intercalate [groupSepLine] $ map (map (hLineContent groupV) . applyRowMods . rows) rowGroups
+    rowGroupLines = maybe concat (\seps -> intercalate [seps]) optGroupSepLine linesPerRowGroup
+    linesPerRowGroup = map rowGroupToLines rowGroups
+    rowGroupToLines = map (horizontalContentLine groupV) . applyRowMods . rows
 
     -- Optional values for the header
     (addHeaderLines, fitHeaderIntoCMIs, realTopH, realTopL, realTopC, realTopR)
                   = case header of
         HeaderHS headerColSpecs hTitles
                ->
-            let headerLine    = hLineContent headerV (zipWith ($) headerRowMods hTitles)
+            let headerLine    = horizontalContentLine headerV (zipWith ($) headerRowMods hTitles)
                 headerRowMods = zipWith3 headerCellModifier
                                          headerColSpecs
                                          cMSs
                                          cMIs
             in
-            ( (headerLine :) . (headerSepLine :)
+            ( (headerLine :) . maybe id (:) optHeaderSepLine
             , fitTitlesCMI hTitles posSpecs
             , headerTopH
             , headerTopL

src/Text/Layout/Table/Primitives/Table.hs

@@ -1,26 +1,45 @@
 -- | This module provides primitives for generating tables. Tables are generated
 -- line by line thus the functions in this module produce 'StringBuilder's that
 -- contain a line.
-module Text.Layout.Table.Primitives.Table where
+module Text.Layout.Table.Primitives.Table
+    ( horizontalDetailLine
+    , optHorizontalDetailLine
+    , horizontalContentLine
+    ) where
 
 import           Data.List
 
 import           Text.Layout.Table.StringBuilder
 import           Text.Layout.Table.Spec.Util
 
 
--- | Draw a horizontal line that will use the delimiters around the
--- appropriately and visually separate by 'hSpace'.
-hLineDetail
+-- | Draw a horizontal line that will use the provided delimiters around
+-- the content appropriately and visually separate by 'hSpace'.
+--
+-- Return 'Nothing' if all delimiters are empty, and 'Just' otherwise.
+optHorizontalDetailLine
     :: StringBuilder b
     => String -- ^ The space characters that are used as padding.
     -> String -- ^ The delimiter that is used on the left side.
     -> String -- ^ The delimiter that is used in between cells.
-    -> String -- ^ The delimiter that is sued on the right side.
+    -> String -- ^ The delimiter that is used on the right side.
+    -> Row b -- ^ A row of builders.
+    -> Maybe b -- ^ The formatted line as a 'StringBuilder', or Nothing if all delimiters are null.
+optHorizontalDetailLine ""     ""     ""     ""     = const Nothing
+optHorizontalDetailLine hSpace delimL delimM delimR = Just . horizontalDetailLine hSpace delimL delimM delimR
+
+-- | Draw a horizontal line that will use the provided delimiters around
+-- the content appropriately and visually separate by 'hSpace'.
+horizontalDetailLine
+    :: StringBuilder b
+    => String -- ^ The space characters that are used as padding.
+    -> String -- ^ The delimiter that is used on the left side.
+    -> String -- ^ The delimiter that is used in between cells.
+    -> String -- ^ The delimiter that is used on the right side.
     -> Row b -- ^ A row of builders.
     -> b -- ^ The formatted line as a 'StringBuilder'.
-hLineDetail hSpace delimL delimM delimR cells =
-    mconcat $ intersperse (stringB hSpace) $ stringB delimL : intersperse (stringB delimM) cells ++ [stringB delimR]
+horizontalDetailLine hSpace delimL delimM delimR cells = mconcat . intersperse (stringB hSpace) $
+    stringB delimL : intersperse (stringB delimM) cells ++ [stringB delimR]
 
 -- | A simplified version of 'hLineDetail' that will use the same delimiter
 -- for everything.
@@ -30,12 +49,12 @@ hLine
     -> String -- ^ The delimiter that is used for everything.
     -> Row b -- ^ A row of builders.
     -> b -- ^ The formatted line as a 'StringBuilder'.
-hLine hSpace delim = hLineDetail hSpace delim delim delim
+hLine hSpace delim = horizontalDetailLine hSpace delim delim delim
 
 -- | Render a line with actual content.
-hLineContent
+horizontalContentLine
     :: StringBuilder b
     => String -- ^ The delimiter that is used for everything.
     -> Row b -- ^ A row of builders.
     -> b
-hLineContent = hLine " "
+horizontalContentLine = hLine " "