lhs2html

lhs2html.lhs

As my first venture into the world of Haskell as a scripting language, I decided to write a small command line tool to automate the task of producing HTML suitable for Blogger posts from Literate Haskell files.

The tool can be invoked on the command line. It takes Literate Haskell on standard input, which it assumes is formatted correctly, and formats the code as HTML on standard output.

> module Main where

> import Data.List ( intercalate )

> isComment ('>':' ':_) = False
> isComment _ = True

> subseqsWhere :: (a -> Bool) -> [a] -> [[a]]
> subseqsWhere p = subseqsWhere' [] [] where
>   subseqsWhere' xss xs [] = if null xs then xss else xss ++ [xs]
>   subseqsWhere' xss xs (x:xs') 
>     | p x = subseqsWhere' xss (xs ++ [x]) xs'
>     | otherwise = subseqsWhere' (if null xs then xss else xss ++ [xs]) [] xs'

> formatLines :: [String] -> String
> formatLines lines = 
>   let encoded = map encodeHtml lines in
>   case (isComment $ head $ lines) of
>     True -> "<p>" ++ (intercalate "\n" encoded) ++ "</p>"
>     False -> "<pre>" ++ (intercalate "<br />" encoded) ++ "</pre>"

> replaceChar x0 repl = flip (>>=) (\x -> if x == x0 then repl else [x])

> encodeHtml = (replaceChar '<' "&lt;") . 
>              (replaceChar '>' "&gt;") .
>              (replaceChar '&' "&amp;")

> process = (map formatLines) . subseqsWhere (not . null)

> main = interact (unlines . process . lines)