「48時間でSchemeを書こう/練習問題の解答」の版間の差分
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マークアップの改善 |
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<syntaxhighlight lang="haskell">
import System
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putStrLn ("Hello, " ++ args !! 0 ++ " " ++ args !! 1)
</syntaxhighlight>
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<syntaxhighlight lang="haskell">
import System
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<code>$</code>演算子によって括弧の数を減らしています。最後の行は<code>$</code>を使わずに<code>print ((read (args !! 0)) + (read $ args !! 1))</code>とも書けます。
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<syntaxhighlight lang="haskell">
import System
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putStrLn $ "あなたの名前は" ++ name ++ "ですね!"
</syntaxhighlight>
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= 練習問題2 =
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▲</ol>
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We need to create a new parser action that accepts a backslash followed by either another backslash or a doublequote. This action needs to return only the second character.
<syntaxhighlight lang="haskell">
escapedChars = do char '\\' -- a backslash </syntaxhighlight>
Once that is done, we need to make some changes to parseString.
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char '"'
return $ String x
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escapedChars :: Parser Char
escapedChars = do char '\\'
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'r' -> '\r'
't' -> '\t'
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First, it is necessary to change the definition of symbol.
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bin2dig' old xs
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data LispVal = Atom String
| List [LispVal]
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<|> try parseBool -- these can all start with the hash char
<|> try parseCharacter
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A possible solution for floating point numbers:
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| Float Double
to the LispVal type.
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'''Ratio''', using Haskell's Ratio type:
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| Complex (Complex Double)
to the LispVal type.
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==Section 4 - Recursive Parsers: Adding lists, dotted lists, and quoted datums==
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