Hi,

 

I want to implement a function in C++ via Haskell FFI, which should have the (final) type of String -> String.

Say, is it possible to re-implement the following function in C++ with the exact same signature?

 

import Data.Char
toUppers:: String -> String
toUppers s = map toUpper senter code here

 

In particular, I wanted to avoid having an IO in the return type because introducing the impurity

(by that I mean the IO monad) for this simple task is logically unnecessary. All examples involing

 a C string I have seen so far involve returning an IO something or Ptr which cannot be converted back to a pure String.

 

The reason I want to do this is that I have the impression that marshaling is not easy with FFI. Maybe

if I can fix the simplest case above (other than primitive types such as int), then I can do whatever data

parsing I want on the C++ side, which should be easy, practically.

 

The cost of parsing is negligible compared to the computation that I want to do between

the marshalling to/from strings.

 

Thanks in advance.