Hi. I recently learned how to use Haskell IArrays and MArrays, and they are quite convenient. I find myself often using some type of MArray for performance reasons, but also some IArray type for array data that is static in a set of computations. Then I started wanting to use arrays inside other kinds of data types, and so quickly ran into the question: what do you do if you want a data type to contain an array, but you don't know in advance what array type you'll be working with (immutable vs. mutible, boxed vs. unboxed). My exploration of this question led to discovering something called GADTs, which allowed me to do definitions like so data Surface a where ISurface :: IArray a e => (a Int Vertex) -> (a Int Face) -> Surface a MSurface :: MArray a e m => (a Int Vertex) -> (a Int Face) -> Surface a Am I heading down the right track here, or is there some better approach? -- https://qlfiles.net My PGP public key ID is 0x340EA95A (pgp.mit.edu).