Poor man's here document
From HaskellWiki
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| + | == Poor man's heredoc / here document == | ||
<haskell> | <haskell> | ||
| - | |||
main = do | main = do | ||
doc <- here "DATA" "Here.hs" [("variable","some"),("substitution","variables")] | doc <- here "DATA" "Here.hs" [("variable","some"),("substitution","variables")] | ||
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</haskell> | </haskell> | ||
| + | |||
| + | == Even poorer man's here-doc / here-document == | ||
| + | |||
| + | If you're just looking to define a multiline string constant, you can just say: | ||
| + | |||
| + | <haskell> | ||
| + | str :: String | ||
| + | str = unlines [ | ||
| + | "Here's a multiline string constant.", | ||
| + | "\tIt's not as convenient as Perl's here-documents,", | ||
| + | "\tbut it does the trick for me." | ||
| + | ] | ||
| + | </haskell> | ||
| + | |||
| + | You can fake interpolation with: | ||
| + | <haskell> | ||
| + | hereDocPraise :: String -> String | ||
| + | hereDocPraise lang = unlines [ | ||
| + | "The language with the best here-document support", | ||
| + | "in my opinion is " ++ lang ++ "." | ||
| + | ] | ||
| + | </haskell> | ||
| + | |||
| + | Disadvantages to poorer man's here-docs: | ||
| + | * You still need to escape special characters. | ||
| + | * It ends with a newline whether you want one or not. | ||
| + | |||
| + | ---- | ||
See Also | See Also | ||
Revision as of 05:20, 20 April 2007
1 Poor man's heredoc / here document
main = do doc <- here "DATA" "Here.hs" [("variable","some"),("substitution","variables")] putStrLn doc html <- here "HTML" "Here.hs" [("code",doc)] putStrLn html here tag file env = do txt <- readFile file let (_,_:rest) = span (/="{- "++tag++" START") (lines txt) (doc,_) = span (/=" "++tag++" END -}") rest return $ unlines $ map subst doc where subst ('$':'(':cs) = case span (/=')') cs of (var,')':cs) -> maybe ("$("++var++")") id (lookup var env) ++ subst cs _ -> '$':'(':subst cs subst (c:cs) = c:subst cs subst "" = "" {- DATA START this is a poor man's here-document with quotes ", and escapes \, and line-breaks, and layout without escaping \" \\ \n, without concatenation. oh, and with $(variable) $(substitution), $(too). DATA END -} {- HTML START <html> <head><title>very important page</title></head> <body> <verb> $(code) </verb> </body> </html> HTML END -}
2 Even poorer man's here-doc / here-document
If you're just looking to define a multiline string constant, you can just say:
str :: String str = unlines [ "Here's a multiline string constant.", "\tIt's not as convenient as Perl's here-documents,", "\tbut it does the trick for me." ]
You can fake interpolation with:
hereDocPraise :: String -> String hereDocPraise lang = unlines [ "The language with the best here-document support", "in my opinion is " ++ lang ++ "." ]
Disadvantages to poorer man's here-docs:
- You still need to escape special characters.
- It ends with a newline whether you want one or not.
See Also
