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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 Lib (exprparser, evaluate, replaceVars)
import Lib (exprparser, evaluate, replaceVars, Expr)
import Data.Map (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)
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 (Left e) = show e
useResult :: Either ParseError Expr -> String
useResult (Right expr) = either id ((showRatio precision) . evaluate) $ replaceVars expr vars
useResult (Left error) = show error
vars :: Map String Rational
vars = Map.fromList [("pi", 245850922 % 78256779), ("e", 271801 % 99990)]

18
src/Lib.hs
View file

@ -1,5 +1,5 @@
module Lib
( exprparser, evaluate, replaceVars
( exprparser, evaluate, replaceVars, Expr
) where
import Control.Applicative((<*))
@ -92,10 +92,17 @@ term = m_parens exprparser
<|> fmap Constant constantInteger
<|> fmap Constant constantRational
replaceVars :: Expr -> Map.Map String Rational -> Expr
replaceVars (Variable name) vs = Constant . maybe (0 % 1) id $ Map.lookup name vs
replaceVars (Binary op a b) vs = Binary op (replaceVars a vs) (replaceVars b vs)
replaceVars (Constant c) vs = Constant c
replaceVars :: Expr -> Map.Map String Rational -> Either String Expr
replaceVars (Constant c) vs = Right $ Constant c
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 (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 (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 Multiply a b) = evaluate a * evaluate b
evaluate (Binary Power a b) = rationalPower (evaluate a) (evaluate b)
evaluate (Variable _) = error "Unreachable Code"