Rewriting code with continuations

Question

I have some code that evaluates primitive programs. Program is a list of statements (expression, block, return statement). Result of evaluation is last evaluated expression.

Answer 1

The translation is fairly mechanical.

Keep in mind that in the continuation monad, return feeds the value into the continuation.

evalStmt :: Statement -> Cont Value Value
evalStmt (Expr val) = 
    let res = Value val
    in return res
evalStmt (Block stmts) = evalBlock stmts
evalStmt (Return val) = cont $ \_ -> Value val

evalBlock :: [Statement] -> Cont Value Value
evalBlock [] = return Undefined
evalBlock [st] = evalStmt st
evalBlock (st:rest) = evalStmt st >> evalBlock rest

evalProgram :: [Statement] -> Value
evalProgram stmts = runCont (evalBlock stmts) id

And to simulate early returns, we just ignore the continuation given to Return val and just return the value we have.