Equivalent of python eval in Haskell

Question

There is function in python called eval that takes string input and evaluates it.

>>> x = 1
>>> print eval('x+1')
2
>>> print eval('12 + 32')
44
>>>  

What is Haskell equivalent of eval function?

Answer 1

This question is asked 11 years ago, and now use the package hint we can define eval very easily, following is an example as self-contained script (you still need nix to run it)

#!/usr/bin/env nix-shell
#! nix-shell -p "haskellPackages.ghcWithPackages (p: with p; [hint])"
#! nix-shell -i "ghci -ignore-dot-ghci -fdefer-type-errors -XTypeApplications"

{-# LANGUAGE ScopedTypeVariables, TypeApplications, PartialTypeSignatures #-}

import Data.Typeable (Typeable)
import qualified Language.Haskell.Interpreter as Hint

-- DOC: https://www.stackage.org/lts-18.18/package/hint-0.9.0.4

eval :: forall t. Typeable t => String -> IO t
eval s = do
    mr <- Hint.runInterpreter $ do
        Hint.setImports ["Prelude"]
        Hint.interpret s (Hint.as :: t)
    case mr of
        Left err -> error (show err)
        Right r -> pure r

-- * Interpret expressions into values:

e1 = eval @Int "1 + 1 :: Int"
e2 = eval @String "\"hello eval\""

-- * Send values from your compiled program to your interpreted program by interpreting a function:

e3 = do
    f <- eval @(Int -> [Int]) "\\x -> [1..x]"
    pure (f 5)