mirror of
https://github.com/pavelchristof/syntax-example.git
synced 2024-09-11 09:55:56 +03:00
107 lines
3.1 KiB
Haskell
107 lines
3.1 KiB
Haskell
{-# LANGUAGE TemplateHaskell #-}
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{-# LANGUAGE FlexibleContexts #-}
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{-# LANGUAGE OverloadedStrings #-}
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import Control.Applicative
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import Control.Lens.Cons
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import Control.Lens.SemiIso
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import Control.Lens.TH
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import qualified Data.Attoparsec.Text.Lazy as AP
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import Data.Char
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import Data.Scientific (Scientific)
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import Data.SemiIsoFunctor
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import Data.Syntax (Syntax)
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import qualified Data.Syntax as S
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import qualified Data.Syntax.Attoparsec.Text.Lazy as S
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import Data.Syntax.Char (SyntaxChar)
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import qualified Data.Syntax.Char as S
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import qualified Data.Syntax.Combinator as S
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import qualified Data.Syntax.Printer.Text as S
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import Data.Text (Text)
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import qualified Data.Text.Lazy.Builder as T
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import qualified Data.Text.Lazy.IO as T
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-- A simple lambda calculus.
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data Literal = LitStr Text
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| LitNum Scientific
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deriving (Show)
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$(makePrisms ''Literal)
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data AST = Var Text
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| Lit Literal
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| App AST AST
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| Abs Text AST
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| Let Text AST AST
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deriving (Show)
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$(makePrisms ''AST)
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-- | A variable name.
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name :: Syntax syn Text => syn Text
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name = _Cons /$/ S.satisfy isAlpha /*/ S.takeWhile isAlphaNum
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-- | A quoted string.
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quoted :: SyntaxChar syn seq => syn seq
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quoted = S.char '"' */ S.takeTill (=='"') /* S.char '"'
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-- | Encloses a symbol in parentheses.
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parens :: SyntaxChar syn seq => syn a -> syn a
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parens m = S.char '(' */ S.spaces_ */ m /* S.spaces_ /* S.char ')'
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-- | A literal.
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literal :: SyntaxChar syn Text => syn Literal
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literal = _LitNum /$/ S.scientific
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/|/ _LitStr /$/ quoted
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-- | An atom is a variable, literal or an expression in parentheses.
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atom :: SyntaxChar syn Text => syn AST
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atom = _Lit /$/ literal
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/|/ _Var /$/ name
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/|/ parens expr
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-- | Parses a list of atoms and folds them with the _App prism.
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apps :: SyntaxChar syn Text => syn AST
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apps = bifoldl1 _App /$/ S.sepBy1 atom S.spaces1
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-- | An expression of our lambda calculus.
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--
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-- Thanks to 'tuple-morph' we don't have to worry about /* and */ here.
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-- Tuples are reassociated and units are removed by the 'morphed'
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-- isomorphism (applied in /$~ operator).
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expr :: SyntaxChar syn Text => syn AST
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expr = _Abs /$~ S.char '\\' /*/ S.spaces_
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/*/ name /*/ S.spaces
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/*/ S.string "->" /*/ S.spaces
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/*/ expr
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/|/ _Let /$~ S.string "let" /*/ S.spaces1
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/*/ name /*/ S.spaces
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/*/ S.char '=' /*/ S.spaces
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/*/ expr /*/ S.spaces1
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/*/ S.string "in" /*/ S.spaces1
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/*/ expr
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/|/ apps
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main :: IO ()
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main = do
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-- Load the standard input.
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t <- T.getContents
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-- Try to parse it.
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case AP.parse (S.getParser expr <* AP.skipSpace <* AP.endOfInput) t of
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AP.Fail _ _ err -> putStrLn err
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AP.Done _ ast -> do
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-- If parsing succeeded print the AST.
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print ast
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-- Try to pretty print it.
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-- (Printing cannot really fail in this example)
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case S.runPrinter expr ast of
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Left err -> putStrLn err
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Right bld -> T.putStrLn (T.toLazyText bld)
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return ()
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