dep-t-advice 0.2.0.1 → 0.3.0.0

raw patch · 5 files changed

+32/−36 lines, 5 filesdep −constraintsPVP ok

version bump matches the API change (PVP)

Dependencies removed: constraints

API changes (from Hackage documentation)

Files

• CHANGELOG.md +7/−2
• README.md +1/−1
• dep-t-advice.cabal +1/−2
• lib/Control/Monad/Dep/Advice.hs +20/−28
• test/tests.hs +3/−3

@@ -1,10 +1,15 @@ # Revision history for dep-t-advice
 
+## 0.3.0.0 
+
+* BREAKING CHANGE. Removed the dependency on "constraints" to reduce the
+  dependency footprint. This changes the signature of restrictArgs.
+
 ## 0.2.0.0 
 
 * BREAKING CHANGE. The Advice type is no longer parameterized by the `cem` and
-  `cr` constraints. Instead, it's directly parameterized by the types @e@ of
-  the environment, @m@ of the base monad and @r@ of the result, which are left
+  `cr` constraints. Instead, it's directly parameterized by the types `e` of
+  the environment, `m` of the base monad and `r` of the result, which are left
   polymorphic when needed. This simplifies a bunch of things. The `ca`
   constraint paramter remains however.
 

@@ -78,7 +78,7 @@ 
 - Change the result value of the function.
 
-- Sidestep the execution of the function altogeher, providing al alternative result.
+- Sidestep the execution of the function altogether, providing al alternative result.
 
 Here's how a `printArgs` advice might be defined:
 

@@ -1,7 +1,7 @@ cabal-version:       3.0
 
 name:                dep-t-advice
-version:             0.2.0.1
+version:             0.3.0.0
 synopsis:            Giving good advice to functions in a DepT environment.
 description:         Companion to the dep-t package. Easily add behaviour to functions living in a DepT environment, 
                      whatever the number of arguments they might have.
@@ -23,7 +23,6 @@ common common
   build-depends:       base >=4.10.0.0 && < 5,
                        sop-core ^>= 0.5.0.0,
-                       constraints ^>= 0.12,
                        dep-t ^>= 0.1.3.0,
   default-language:    Haskell2010
 

@@ -101,19 +101,14 @@     NP (..),
     I (..),
     cfoldMap_NP,
-
-    -- * "constraints" re-exports
-    -- $constraints
-    type (:-) (..),
-    Dict (..),
+    Dict (..)
   )
 where
 
 import Control.Monad.Dep
-import Data.Constraint
 import Data.Kind
 import Data.SOP
-import Data.SOP.Dict qualified as SOP
+import Data.SOP.Dict
 import Data.SOP.NP
 
 -- $setup
@@ -131,7 +126,6 @@ -- >>> import Control.Monad.Dep
 -- >>> import Control.Monad.Dep.Advice
 -- >>> import Control.Monad.Dep.Advice.Basic (printArgs,returnMempty)
--- >>> import Data.Constraint
 -- >>> import Data.Kind
 -- >>> import Data.SOP
 -- >>> import Data.SOP.NP
@@ -484,30 +478,34 @@ --    normal function constraints—the @ca@ constraints of an 'Advice' aren't
 --    automatically "collected" during composition.
 --
---    Instead, we need to harmonize the @ca@ constraints of each 'Advice' by turning them
---    into the combination of all constraints. 'restrictArgs' helps with that.
+--    Instead, we need to harmonize the @ca@ constraints of each 'Advice' by
+--    turning them into the combination of all constraints. 'restrictArgs'
+--    helps with that.
 --
---    'restrictArgs' takes as parameter evidence of entailment between @ca@
---    constraints, using the type '(:-)' from the \"constraints\" package.  But
---    how to construct such evidence? By using the 'Sub' and the 'Dict'
---    constructors, either with an explicit type signature:
+--    'restrictArgs' takes as parameter value-level "\evidence\" that one
+--    constraint implies another. But how to construct such evidence? By using
+--    the 'Dict' GADT, more precisely the deceptively simple-looking term
+--    @\\Dict -> Dict@. That function "absorbs" some constraint present in the
+--    ambient context and re-packages it a a new constraint that is implied by
+--    the former. We can't rely on type inference here; we need to provide
+--    enough type information to the GADT, be it as an explicit signature:
 --
 -- >>> :{
 --  stricterPrintArgs :: forall e m r. MonadIO m => Advice (Show `And` Eq `And` Ord) NilEnv m r
---  stricterPrintArgs = restrictArgs (Sub Dict) (printArgs stdout "foo")
+--  stricterPrintArgs = restrictArgs (\Dict -> Dict) (printArgs stdout "foo")
 -- :}
 --
 --    or with a type application to 'restrictArgs':
 --
--- >>> stricterPrintArgs = restrictArgs @(Show `And` Eq `And` Ord) (Sub Dict) (printArgs stdout "foo")
+-- >>> stricterPrintArgs = restrictArgs @(Show `And` Eq `And` Ord) (\Dict -> Dict) (printArgs stdout "foo")
 --
 --
 
 -- | Makes the constraint on the arguments more restrictive.
 restrictArgs ::
   forall more less e m r.
-  -- | Evidence that one constraint implies the other.
-  (forall x. more x :- less x) ->
+  -- | Evidence that one constraint implies the other. Every @x@ that has a @more@ instance also has a @less@ instance.
+  (forall x. Dict more x -> Dict less x) -> 
   -- | Advice with less restrictive constraint on the args.
   Advice less e m r ->
   -- | Advice with more restrictive constraint on the args.
@@ -523,7 +521,7 @@ restrictArgs evidence (Advice proxy tweakArgs tweakExecution) =
   let captureExistential ::
         forall more less e m r u.
-        (forall x. more x :- less x) ->
+        (forall x. Dict more x -> Dict less x) ->
         Proxy u ->
         ( forall as.
           All less as =>
@@ -540,19 +538,13 @@         Advice
           (Proxy @u)
           ( let tweakArgs'' :: forall as. All more as => NP I as -> DepT e m (u, NP I as)
-                tweakArgs'' = case SOP.mapAll @more @less (translateEvidence @more @less evidence') of
-                  f -> case f (SOP.Dict @(All more) @as) of
-                    SOP.Dict -> \args -> tweakArgs' @as args
+                tweakArgs'' = case Data.SOP.Dict.mapAll @more @less evidence' of
+                  f -> case f (Dict @(All more) @as) of
+                    Dict -> \args -> tweakArgs' @as args
              in tweakArgs''
           )
           tweakExecution'
    in captureExistential evidence proxy tweakArgs tweakExecution
-
-
-translateEvidence :: forall more less a. (forall x. more x :- less x) -> SOP.Dict more a -> SOP.Dict less a
-translateEvidence evidence SOP.Dict =
-  case evidence @a of
-    Sub Dict -> SOP.Dict @less @a
 
 -- $sop
 -- Some useful definitions re-exported the from \"sop-core\" package.

@@ -29,6 +29,7 @@ import Test.Tasty.HUnit
 import Prelude hiding (log)
 import Data.Proxy
+import System.IO
 
 -- Some helper typeclasses.
 --
@@ -254,9 +255,8 @@ returnMempty'' :: forall ca e m r. (Monad m, Monoid r, Show r, Read r) => Advice ca e m r
 returnMempty'' = returnMempty <> justAResultConstraint
 
--- 
--- returnMempty'' = restrictResult @(Monoid `And` Show) (Sub Dict) returnMempty
--- 
+printArgs' = restrictArgs @(Eq `And` Ord `And` Show) (\Dict -> Dict) (printArgs @NilEnv @IO stdout "foo")
+ 
 -- does EnvConstraint compile?
 
 -- type FooAdvice = Advice Top (EnvConstraint (MustBe NilEnv)) Top