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|
module Error (
LispError (..)
, LispResult (..)
, unwrap
) where
import Control.Monad.Except
import Parser
import Text.ParserCombinators.Parsec
data LispError = Parse ParseError
| BadForm String Expr
| ArgCount Int [Expr]
| UnknownFunction String
| TypeMismatch String Expr
unwordsList :: [Expr] -> String
unwordsList = unwords . map show
instance Show LispError where
show (Parse e) = "Parser Error: " ++ show e
show (BadForm s expr) = "Bad Form: " ++ s ++ ": " ++ show expr
show (ArgCount n es) = "Invalid arity, expected " ++ show n ++ ", got value(s): " ++ unwordsList es
show (UnknownFunction fn) = "Cannot apply function: " ++ fn
show (TypeMismatch msg got) = "Type mismatch, expected " ++ msg ++ ", got: " ++ show got
type LispResult = Either LispError
unwrap :: LispResult t -> t
unwrap (Right v) = v
unwrap (Left _) = undefined -- should panic
|
