blob: dcbfdb1ad96c2a3fa1c07f2f1fef5d16b94a7a39 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
|
module Parser ( parseLispValue
, Expr(..)
, parseString
, parseInt
, parseFloat
, parseAtom
, parseList
, parseQuote
, parseDottedList
) where
import Control.Applicative ((<$>))
import Control.Monad (liftM)
import Text.ParserCombinators.Parsec
type Ident = String
data Expr = List [Expr]
| DottedList [Expr] Expr
| StringLiteral String
| IntLiteral Integer
| FloatLiteral Double
| BoolLiteral Bool
| Id Ident
deriving (Eq)
parseString :: Parser Expr
parseString = do
char '"'
innards <- many (noneOf "\"")
char '"'
return (StringLiteral innards)
parseInt :: Parser Expr
parseInt = IntLiteral . read <$> many1 digit
parseFloat :: Parser Expr
parseFloat = do
characteristic <- many digit
char '.'
mantissa <- many1 digit
return $ (FloatLiteral . read) $ characteristic ++ "." ++ mantissa
symbol :: Parser Char
symbol = oneOf "!#$%&|*+:/-=<?>@^_~"
parseAtom :: Parser Expr
parseAtom = do
first <- letter <|> symbol
rest <- many (letter <|> symbol <|> digit)
let atom = first:rest
return $ case atom of
"#t" -> BoolLiteral True
"#f" -> BoolLiteral False
_ -> Id atom
whiteSpace :: Parser ()
whiteSpace = skipMany1 space
parseList :: Parser Expr
parseList = List <$> sepBy parseLispValue whiteSpace
parseDottedList :: Parser Expr
parseDottedList = do
head <- endBy parseLispValue whiteSpace
char '.'
whiteSpace
DottedList head <$> parseLispValue
parseQuote :: Parser Expr
parseQuote = do
char '\''
x <- parseLispValue
return $ List [Id "quote", x]
parseLispValue :: Parser Expr
parseLispValue =
try parseAtom
<|> parseString
<|> parseInt
<|> parseQuote
-- TODO: figure out a way to have floats and dotted lists
-- <|> parseFloat
<|> do
char '('
x <- try parseList <|> parseDottedList
char ')'
return x
<?> "expected lisp value!"
instance Show Expr where
show (DottedList xs x) = "(" ++ unwords (map show xs) ++ " . " ++ show x ++ ")"
show (List xs) = "(" ++ unwords (map show xs) ++ ")"
show (StringLiteral s) = "\"" ++ s ++ "\""
show (IntLiteral n) = show n
show (FloatLiteral n) = show n
show (BoolLiteral True) = "#t"
show (BoolLiteral False) = "#f"
show (Id i) = i
|
