1 files changed, 121 insertions, 0 deletions
diff --git a/Biz/Language/Bs/Parser.hs b/Biz/Language/Bs/Parser.hs
new file mode 100644
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--- /dev/null
+++ b/Biz/Language/Bs/Parser.hs
@@ -0,0 +1,121 @@
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE NoImplicitPrelude #-}
+module Language.Bs.Parser (
+  readExpr
+, readExprFile
+) where
+
+import Control.Monad (fail)
+import Control.Monad (mzero)
+import Data.Char (digitToInt)
+import Data.Functor.Identity (Identity)
+import Data.String
+import qualified Data.Text as T
+import Language.Bs.Expr
+import Protolude hiding ((<|>), try)
+import Text.Parsec
+import qualified Text.Parsec.Language as Lang
+import Text.Parsec.Text
+import qualified Text.Parsec.Token as Tok
+
+lexer :: Tok.GenTokenParser T.Text () Identity
+lexer = Tok.makeTokenParser style
+
+style :: Tok.GenLanguageDef T.Text () Identity
+style = Lang.emptyDef {
+  Tok.commentStart = "#|"
+  , Tok.commentEnd = "|#"
+  , Tok.commentLine = ";"
+  , Tok.opStart = mzero
+  , Tok.opLetter = mzero
+  , Tok.identStart = letter <|> oneOf "!$%&*/:<=>?^_~"
+  , Tok.identLetter = digit <|> letter <|> oneOf "!$%&*/:<=>?^_~+-.@"
+  }
+
+parens :: Parser a -> Parser a
+parens = Tok.parens lexer
+
+whitespace :: Parser ()
+whitespace = Tok.whiteSpace lexer
+
+lexeme :: Parser a -> Parser a
+lexeme = Tok.lexeme lexer
+
+quoted :: Parser a -> Parser a
+quoted p = try (char '\'') *> p
+
+identifier :: Parser T.Text
+identifier = T.pack <$> (Tok.identifier lexer <|> specialIdentifier) <?> "identifier"
+  where
+  specialIdentifier :: Parser String
+  specialIdentifier = lexeme $ try $
+    string "-" <|> string "+" <|> string "..."
+
+-- | The @Radix@ type consists of a base integer (e.g. @10@) and a parser for
+-- digits in that base (e.g. @digit@).
+type Radix = (Integer, Parser Char)
+
+-- | Parse an integer, given a radix as output by @radix@.
+-- Copied from Text.Parsec.Token
+numberWithRadix :: Radix -> Parser Integer
+numberWithRadix (base, baseDigit) = do
+  digits <- many1 baseDigit
+  let n = foldl (\x d -> base*x + toInteger (digitToInt d)) 0 digits
+  seq n (return n)
+
+decimal :: Parser Integer
+decimal = Tok.decimal lexer
+
+-- | Parse a sign, return either @id@ or @negate@ based on the sign parsed.
+-- Copied from Text.Parsec.Token
+sign :: Parser (Integer -> Integer)
+sign = char '-' *> return negate
+   <|> char '+' *> return identity
+   <|> return identity
+
+intRadix :: Radix -> Parser Integer
+intRadix r = sign <*> numberWithRadix r
+
+textLiteral :: Parser T.Text
+textLiteral = T.pack <$> Tok.stringLiteral lexer
+
+nil :: Parser ()
+nil = try ((char '\'') *> string "()") *> return () <?> "nil"
+
+hashVal :: Parser Expr
+hashVal = lexeme $ char '#'
+  *> (char 't' *> return (Bool True)
+  <|> char 'f' *> return (Bool False)
+  <|> char 'b' *> (Numb <$> intRadix (2, oneOf "01"))
+  <|> char 'o' *> (Numb <$> intRadix (8, octDigit))
+  <|> char 'd' *> (Numb <$> intRadix (10, digit))
+  <|> char 'x' *> (Numb <$> intRadix (16, hexDigit))
+  <|> oneOf "ei" *> fail "Unsupported: exactness"
+  <|> char '(' *> fail "Unsupported: vector"
+  <|> char '\\' *> fail "Unsupported: char")
+
+
+lispVal :: Parser Expr
+lispVal = hashVal
+  <|> Nil <$ nil
+  <|> Numb <$> try (sign <*> decimal)
+  <|> Atom <$> identifier
+  <|> Tape <$> textLiteral
+  <|> _Quote <$> quoted lispVal
+  <|> List <$> parens manyExpr
+
+manyExpr :: Parser [Expr]
+manyExpr = lispVal `sepBy` whitespace
+
+_Quote :: Expr -> Expr
+_Quote x = List [Atom "quote", x]
+
+contents :: Parser a -> ParsecT T.Text () Identity a
+contents p = whitespace *> lexeme p <* eof
+
+readExpr :: T.Text -> Either ParseError Expr
+readExpr = parse (contents lispVal) "<stdin>"
+
+readExprFile :: SourceName -> T.Text -> Either ParseError Expr
+readExprFile = parse (contents (List <$> manyExpr))