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Error out for undefined variables

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VegOwOtenks 2024-09-16 11:38:22 +02:00
parent 16aca9a66b
commit 9e7ad28c5c
2 changed files with 17 additions and 8 deletions
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7
app/Main.hs
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@ -2,7 +2,7 @@ module Main (main) where
import Text.Parsec import Text.Parsec
import Lib (exprparser, evaluate, replaceVars) import Lib (exprparser, evaluate, replaceVars, Expr)
import Data.Map (Map) import Data.Map (Map)
import qualified Data.Map as Map import qualified Data.Map as Map
@ -21,8 +21,9 @@ showRatio p r = (if (r < 0) then "-" else "") ++ prepoint_digits ++ (if (length
prepoint_digits = init . show . round . abs $ (r * 10) prepoint_digits = init . show . round . abs $ (r * 10)
postpoint_digits = reverse .dropWhile (=='0') . reverse .(take p) . (drop (length prepoint_digits)) . show . round . abs $ (r * 10^p) postpoint_digits = reverse .dropWhile (=='0') . reverse .(take p) . (drop (length prepoint_digits)) . show . round . abs $ (r * 10^p)
useResult (Right e) = (showRatio precision) . evaluate $ replaceVars e vars useResult :: Either ParseError Expr -> String
useResult (Left e) = show e useResult (Right expr) = either id ((showRatio precision) . evaluate) $ replaceVars expr vars
useResult (Left error) = show error
vars :: Map String Rational vars :: Map String Rational
vars = Map.fromList [("pi", 245850922 % 78256779), ("e", 271801 % 99990)] vars = Map.fromList [("pi", 245850922 % 78256779), ("e", 271801 % 99990)]

18
src/Lib.hs
View file

@ -1,5 +1,5 @@
module Lib module Lib
( exprparser, evaluate, replaceVars ( exprparser, evaluate, replaceVars, Expr
) where ) where
import Control.Applicative((<*)) import Control.Applicative((<*))
@ -92,10 +92,17 @@ term = m_parens exprparser
<|> fmap Constant constantInteger <|> fmap Constant constantInteger
<|> fmap Constant constantRational <|> fmap Constant constantRational
replaceVars :: Expr -> Map.Map String Rational -> Expr replaceVars :: Expr -> Map.Map String Rational -> Either String Expr
replaceVars (Variable name) vs = Constant . maybe (0 % 1) id $ Map.lookup name vs replaceVars (Constant c) vs = Right $ Constant c
replaceVars (Binary op a b) vs = Binary op (replaceVars a vs) (replaceVars b vs) replaceVars (Variable name) vs = maybe (Left ("Usage of unknown variable: '" ++ name ++ "'\nSuggestion: define the variable\n++ " ++ name ++ "=42")) (Right . Constant . id) $ Map.lookup name vs
replaceVars (Constant c) vs = Constant c replaceVars (Binary op l r) vs = case leftBranch of
Left s -> Left s
Right a -> case rightBranch of
Left s -> Left s
Right b -> Right $ Binary op a b
where
leftBranch = replaceVars l vs
rightBranch = replaceVars r vs
evaluate :: Expr -> Rational evaluate :: Expr -> Rational
evaluate (Constant c) = c evaluate (Constant c) = c
@ -104,3 +111,4 @@ evaluate (Binary Minus a b) = evaluate a - evaluate b
evaluate (Binary Divide a b) = evaluate a / evaluate b evaluate (Binary Divide a b) = evaluate a / evaluate b
evaluate (Binary Multiply a b) = evaluate a * evaluate b evaluate (Binary Multiply a b) = evaluate a * evaluate b
evaluate (Binary Power a b) = rationalPower (evaluate a) (evaluate b) evaluate (Binary Power a b) = rationalPower (evaluate a) (evaluate b)
evaluate (Variable _) = error "Unreachable Code"