我正在尝试为一种简单的函数式语言制作解析器,有点像 Caml,但我似乎被最简单的东西困住了。
所以我想知道是否有一些更完整的parsec
解析器示例,超越“这就是你解析 2 + 3 的方式”。尤其是术语等方面的函数调用。
而且我读过“给你写一个方案”,但方案的语法很简单,对学习没有帮助。
我遇到的最大问题是如何正确使用try
,因为我真的不明白为什么 parsec 似乎从来没有使用这个解析器解析为函数调用:<|>
choice
a(6)
expr = choice [number, call, ident]
number = liftM Number float <?> "Number"
ident = liftM Identifier identifier <?> "Identifier"
call = do
name <- identifier
args <- parens $ commaSep expr
return $ FuncCall name args
<?> "Function call"
编辑添加了一些完成代码,尽管这实际上不是我问的:
AST.hs
module AST where
data AST
= Number Double
| Identifier String
| Operation BinOp AST AST
| FuncCall String [AST]
deriving (Show, Eq)
data BinOp = Plus | Minus | Mul | Div
deriving (Show, Eq, Enum)
Lexer.hs
module Lexer (
identifier, reserved, operator, reservedOp, charLiteral, stringLiteral,
natural, integer, float, naturalOrFloat, decimal, hexadecimal, octal,
symbol, lexeme, whiteSpace, parens, braces, angles, brackets, semi,
comma, colon, dot, semiSep, semiSep1, commaSep, commaSep1
) where
import Text.Parsec
import qualified Text.Parsec.Token as P
import Text.Parsec.Language (haskellStyle)
lexer = P.makeTokenParser haskellStyle
identifier = P.identifier lexer
reserved = P.reserved lexer
operator = P.operator lexer
reservedOp = P.reservedOp lexer
charLiteral = P.charLiteral lexer
stringLiteral = P.stringLiteral lexer
natural = P.natural lexer
integer = P.integer lexer
float = P.float lexer
naturalOrFloat = P.naturalOrFloat lexer
decimal = P.decimal lexer
hexadecimal = P.hexadecimal lexer
octal = P.octal lexer
symbol = P.symbol lexer
lexeme = P.lexeme lexer
whiteSpace = P.whiteSpace lexer
parens = P.parens lexer
braces = P.braces lexer
angles = P.angles lexer
brackets = P.brackets lexer
semi = P.semi lexer
comma = P.comma lexer
colon = P.colon lexer
dot = P.dot lexer
semiSep = P.semiSep lexer
semiSep1 = P.semiSep1 lexer
commaSep = P.commaSep lexer
commaSep1 = P.commaSep1 lexer
Parser.hs
module Parser where
import Control.Monad (liftM)
import Text.Parsec
import Text.Parsec.String (Parser)
import Lexer
import AST
expr = number <|> callOrIdent
number = liftM Number float <?> "Number"
callOrIdent = do
name <- identifier
liftM (FuncCall name) (parens $ commaSep expr) <|> return (Identifier name)