Pretty.hs

module Text.Sifflet.Pretty 
    (Pretty(..)
    , indentLine, sepLines, sepLines2
    , sepComma, sepCommaSp, sepSpace)

where

import Data.List (intercalate)


-- | The class of types that can be pretty-printed.
-- (Unfortunately this is not very useful, because
-- and Expr can be pretty Haskell or pretty Python or pretty Scheme,
-- leading to overlapping instance declarations.)
--
-- pretty x is a pretty String representation of x.
-- prettyList prefix infix postfix xs is a pretty String representation
--    of the list xs, with prefix, infix, and postfix specifying the
--    punctuation.  For example, if (pretty x) => "x",
--    then prettyList "[" ", " "]" [x, x, x] => "[x, x, x]".
--
-- Minimal complete implementation: define pretty.

class Pretty a where

    pretty :: a -> String

    prettyList :: String -> String -> String -> [a] -> String
    prettyList pre tween post xs =
        pre ++ intercalate tween (map pretty xs) ++ post

-- | Indent a single line n spaces.
indentLine :: Int -> String -> String
indentLine n line = replicate n ' ' ++ line

-- | sepLines is like unlines, but omits the \n at the end of the
-- last line.
sepLines :: [String] -> String
sepLines = intercalate "\n"

-- | sepLines2 is like sepLines, but adds an extra \n between each
-- pair of lines so they are "double spaced."
sepLines2 :: [String] -> String
sepLines2 = intercalate "\n\n"

-- | Separate strings by commas and nothing else (",")
sepComma :: [String] -> String
sepComma = intercalate ","

-- | Separate strings by commas and spaces (", ")
sepCommaSp :: [String] -> String
sepCommaSp = intercalate ", "

-- | Separate strings by just spaces (" ")
sepSpace :: [String] -> String
sepSpace = unwords