Don't use empty output delimiters unless requested

In particular, while input delimiters are usually used for the default
output delimiters, setting empty input delimiters to specify the
line-based or the stream based input format should not cause the output
delimiters to be empty.

runtime/System/Console/Hawk/Args/Spec.hs

@@ -66,8 +66,9 @@ data Separator = Whitespace | Delimiter Delimiter
   deriving (Show, Eq)
 
 fromSeparator :: Separator -> Delimiter
-fromSeparator Whitespace    = " "
-fromSeparator (Delimiter d) = d
+fromSeparator Whitespace     = " "
+fromSeparator (Delimiter "") = " "
+fromSeparator (Delimiter d)  = d
 
 
 newtype ContextSpec = ContextSpec

src/System/Console/Hawk/Args/Parse.hs

@@ -104,7 +104,7 @@ inputSpec (rSep, fSep) = InputSpec <$> source <*> format
 -- 
 -- >>> test ["-D;", "-d", "-a", "L.reverse"]
 -- UseStdout
--- (";","")
+-- (";"," ")
 -- 
 -- >>> test ["-o\t", "-d,", "-O|"]
 -- UseStdout

tests/System/Console/Hawk/PreludeTests.hs

@@ -81,6 +81,25 @@ testEval flags expr = test flags expr ""
 --     parse error (possibly incorrect indentation or mismatched brackets)
 -- *** Exception: ExitFailure 1
 -- 
+-- Making sure that setting line-mode or stream-mode doesn't affect the output format
+-- unless specifically requested:
+-- 
+-- >>> testPrelude "default" ["-d", "-m"]       "\\x -> ('a', x, 'b')" "1-3"
+-- a 1 b
+-- a 2 b
+-- a 3 b
+-- 
+-- >>> testPrelude "default" ["-d", "-o", "-m"] "\\x -> ('a', x, 'b')" "1-3"
+-- a1b
+-- a2b
+-- a3b
+-- 
+-- >>> testPrelude "default" ["-D", "-a"]       "\\x -> ('a', x, 'b')" "equation"
+-- a x1*y1*z1 + x2*y2*z2 b
+-- 
+-- >>> testPrelude "default" ["-D", "-O", "-a"] "\\x -> ('a', x, 'b')" "equation"
+-- ax1*y1*z1 + x2*y2*z2b
+-- 
 -- Making sure that we don't assume the user prelude exports "map":
 -- 
 -- >>> testPrelude "set" ["-m"] "const $ \"hello\"" "1-3"