On 20.01.2012 00:37, Nicholas Tung wrote:

Dear all,

    I wanted to voice support for a partial type annotations. Here's my
usage scenario: I have a monad for an imperative EDSL, which has an
associated expression data type,

I wanted such extension more than once. For me it's useful when compiler can almost infer type and only few type variables are actually required. Now I have to either type full signature or invert functions a la `asTypeOf'

class (Monad m, Expression (ExprTyp m)) => MyDSLMonad m where
    data ExprTyp m :: * -> *

    and you write imperative EDSL code like so,

my_code_block = do
    x <- instruction1
    y <- instruction2 (x + x)
    ...

    I want the user to be able to annotate "x is an Integer". However,
to do that now, one has to now add a type signature for my_code_block
like so, so that the $m$ variable is in scope,

my_code_block :: forall m. MyDSLMonad m => m ()
my_code_block = do
    x :: ExprTyp m Integer <- instruction1

Actually it should be

> my_code_block :: ...
> my_code_block = do
>   x :: Integer <- instruction1 -- Require ScopedTypeVariables

or

>   x <- instruction1 :: Expr Integer

or with partial type signatures

>   x <- instruction1 :: _ _ Integer

or wiht

>   x <- instruction1
>   y <- instrunctio2 (x + x :: Integer)