Write You a Haskell Stephen Diehl

Let x e body -> do
e’ do
VBool br do
eval env (App e (Fix e))
binop :: Binop -> Integer -> Integer -> Value
binop Add a b = VInt $ a + b
binop Mul a b = VInt $ a * b
binop Sub a b = VInt $ a - b
binop Eql a b = VBool $ a == b
Interactive Shell
Our language has now grown out the small little shells we were using before, and now we need something
much more robust to hold the logic for our interactive interpreter.
We will structure our REPL as a monad wrapped around IState (the interpreter state) datatype. We will
start to use the repline library from here out which gives us platform independent readline, history, and
tab completion support.
data IState = IState
{ tyctx :: TypeEnv -- Type environment
, tmctx :: TermEnv -- Value environment
}
initState :: IState
initState = IState emptyTyenv emptyTmenv
type Repl a = HaskelineT (StateT IState IO) a
hoistErr :: Show e => Either e a -> Repl a
hoistErr (Right val) = return val
hoistErr (Left err) = do
liftIO $ print err
abort
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