Implement new Coercion rules

.github/workflows/test.yml

@@ -24,7 +24,7 @@ jobs:
       with:
         repository: 'dfinity/candid'
         path: candid
-        ref: ab15036543c10066d0b5c266de2108e9e0133e0a
+        ref: 9b0e92e8729e660bfdcf02a3169b9a4b829762a4
 
     - uses: haskell/actions/setup@v1
       with:

candid.cabal

@@ -41,6 +41,7 @@ library
         Codec.Candid.EncodeTextual
         Codec.Candid.Encode
         Codec.Candid.Infer
+        Codec.Candid.Subtype
         Codec.Candid.Coerce
 
     default-language: Haskell2010
@@ -89,6 +90,7 @@ test-suite test
     hs-source-dirs:   test
     other-modules:
         SpecTests
+        Tests
         THTests
 
     default-language: Haskell2010

src/Codec/Candid.hs

@@ -118,6 +118,7 @@ Candid is inherently typed, so before encoding or decoding, you have to indicate
  , unescapeFieldName
  , candidHash
  , Value(..)
+ , isSubtypeOf
 
 -- ** Dynamic use
 
@@ -150,6 +151,7 @@ import Codec.Candid.TypTable
 import Codec.Candid.Decode
 import Codec.Candid.Encode
 import Codec.Candid.EncodeTextual
+import Codec.Candid.Subtype
 
 -- $setup
 -- >>> :set -dppr-cols=200

src/Codec/Candid/Class.hs

@@ -73,8 +73,7 @@ decode b = do
     -- Decode
     (ts, vs) <- decodeVals b
     -- Coerce to expected type
-    c <- coerceSeqDesc ts (buildSeqDesc (asTypes @(AsTuple a)))
-    vs' <- c vs
+    vs' <- coerceSeqDesc vs ts (buildSeqDesc (asTypes @(AsTuple a)))
     fromCandidVals vs'
 
 -- | Decode (dynamic) values to Haskell type
@@ -106,9 +105,12 @@ class CandidSeq a where
 seqDesc :: forall a. CandidArg a => SeqDesc
 seqDesc = buildSeqDesc (asTypes @(AsTuple a))
 
+typeGraph :: forall a. Candid a => Type (Ref TypeRep Type)
+typeGraph = asType @(AsCandid a)
+
 -- | NB: This will loop with recursive types!
 typeDesc :: forall a. Candid a => Type Void
-typeDesc = asType @(AsCandid a) >>= go
+typeDesc = typeGraph @a >>= go
   where go (Ref _ t) = t >>= go
 
 instance Pretty TypeRep where