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)