Difference between revisions of "Poor man's here document"
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<haskell> |
<haskell> |
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main = do |
main = do |
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doc <- here "DATA" "Here.hs" [("variable","some"),("substitution","variables")] |
doc <- here "DATA" "Here.hs" [("variable","some"),("substitution","variables")] |
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</haskell> |
</haskell> |
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| + | == Even poorer man's here-doc / here-document == |
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| + | |||
| + | If you're just looking to define a multiline string constant, you can just say: |
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| + | |||
| + | <haskell> |
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| + | str :: String |
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| + | str = unlines [ |
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| + | "Here's a multiline string constant.", |
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| + | "\tIt's not as convenient as Perl's here-documents,", |
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| + | "\tbut it does the trick for me." |
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| + | ] |
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| + | </haskell> |
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| + | |||
| + | You can fake interpolation with: |
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| + | <haskell> |
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| + | hereDocPraise :: String -> String |
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| + | hereDocPraise lang = unlines [ |
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| + | "The language with the best here-document support", |
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| + | "in my opinion is " ++ lang ++ "." |
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| + | ] |
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| + | </haskell> |
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| + | |||
| + | Disadvantages to poorer man's here-docs: |
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| + | * You still need to escape special characters. |
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| + | * It ends with a newline whether you want one or not. |
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| + | |||
| + | ---- |
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See Also |
See Also |
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Revision as of 05:20, 20 April 2007
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 -}
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