58 lines
1.8 KiB
Plaintext
58 lines
1.8 KiB
Plaintext
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> -- | This module contains some generic combinators used in the
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> -- parser. None of the parsing which relies on the local lexers is
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> -- in this module. Some of these combinators have been taken from
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> -- other parser combinator libraries other than Parsec.
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> module Language.SQL.SimpleSQL.Combinators
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> (optionSuffix
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> ,(<??>)
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> ,(<$$>)
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> ,(<??.>)
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> ,(<??*>)) where
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> import Control.Applicative ((<$>), (<*>), (<**>))
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> import Text.Parsec (option,many)
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> import Text.Parsec.String (Parser)
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a possible issue with the option suffix is that it enforces left
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associativity when chaining it recursively. Have to review
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all these uses and figure out if any should be right associative
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instead, and create an alternative suffix parser
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This function style is not good, and should be replaced with chain and
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<??> which has a different type
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> optionSuffix :: (a -> Parser a) -> a -> Parser a
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> optionSuffix p a = option a (p a)
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parses an optional postfix element and applies its result to its left
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hand result, taken from uu-parsinglib
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TODO: make sure the precedence higher than <|> and lower than the
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other operators so it can be used nicely
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> (<??>) :: Parser a -> Parser (a -> a) -> Parser a
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> p <??> q = p <**> option id q
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this is analogous to <**>, flipped <$>
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> (<$$>) :: (a -> b -> c) -> Parser b -> Parser (a -> c)
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> (<$$>) = (<$>) . flip
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composing suffix parsers, not sure about the name. This is used to add
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a second or more suffix parser contingent on the first suffix parser
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succeeding.
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> (<??.>) :: Parser (a -> a) -> Parser (a -> a) -> Parser (a -> a)
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> (<??.>) pa pb = (.) <$$> pa <*> option id pb
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0 to many repeated applications of suffix parser
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> (<??*>) :: Parser a -> Parser (a -> a) -> Parser a
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> p <??*> q = foldr ($) <$> p <*> (reverse <$> many q)
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