In the spirit of Oleg's hack, but with nicer combinator support, you can
use the patch combinators I just uploaded to Hackage (prompted by this
thread):
http://hackage.haskell.org/package/patch-combinators
Your example then becomes:
my_code_block = do
x <- instruction1 -:: tCon (tCon tInteger)
y <- instruction2 (x + x)
The signature `tCon (tCon tInteger)` should be read as the type `_ (_
Integer)`.
Alternatively, with ViewPatterns, you can write:
my_code_block2 = do
(tCon tInteger -> x) <- instruction1
y <- instruction2 (x + x)
return y
/ Emil
2012-01-19 21:37, Nicholas Tung skrev:
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,
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
...
If such a feature were available, one could write a nice type
synonym "Expr" and use it like so,
type Expr a = ExprTyp _ a
my_code_block = do
x :: Expr Integer <- instruction1
Suggestions for workarounds are appreciated. I created an
`asExprTypeOf`, similar to Prelude's `asExprTyp`, but I don't like the
syntax as much.
Some previous discussion
* http://www.haskell.org/pipermail/haskell/2002-April/009409.html
* (a reply) http://www.haskell.org/pipermail/haskell/2002-April/009413.html
* http://hackage.haskell.org/trac/haskell-prime/wiki/PartialTypeAnnotations
cheers,
Nicholas — https://ntung.com — 4432-nstung
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