Merge pull request #20 from nomeata/joachim/subtype

Implement new Coercion rules

.github/workflows/test.yml

@@ -25,7 +25,7 @@ jobs:
       with:
         repository: 'dfinity/candid'
         path: candid
-        ref: ab15036543c10066d0b5c266de2108e9e0133e0a
+        ref: 6edd82f928b6242c596003ced00ffc8e099ee04e
 
     - uses: haskell/actions/setup@v1
       with:

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Revision history for haskell-candid
 
+## 0.4-- 2022-11-05
+
+* Fix did file parsing bug: Allow underscores in unicode escapes
+* Implement the new subtyping rules from spec version 0.1.4
+  https://github.com/dfinity/candid/pull/311
+
 ## 0.3.2.1 -- 2022-12-01
 
 * GHC-9.2 compatibility

candid.cabal

@@ -1,6 +1,6 @@
 cabal-version:      >=1.10
 name:               candid
-version:            0.3.2.1
+version:            0.4
 license:            Apache
 license-file:       LICENSE
 maintainer:         [email protected]
@@ -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

@@ -1,8 +1,6 @@
 {-|
 
-This module provides preliminary Haskell supprot for decoding and encoding the __Candid__ data format. See <https://github.com/dfinity/candid/blob/master/spec/Candid.md> for the official Candid specification.
-
-__Warning:__ The interface of this library is still in flux, as we are yet learning the best idioms around Candid and Haskell.
+This module provides Haskell support for decoding and encoding the __Candid__ data format. See <https://github.com/dfinity/candid/blob/master/spec/Candid.md> for the official Candid specification.
 
 -}
 
@@ -49,7 +47,6 @@ Candid is inherently typed, so before encoding or decoding, you have to indicate
 {- |
 
 * Generating interface descriptions (.did files) from Haskell functions
-* Future types
 * Parsing the textual representation dynamically against an expected type
 
 -}
@@ -118,6 +115,7 @@ Candid is inherently typed, so before encoding or decoding, you have to indicate
  , unescapeFieldName
  , candidHash
  , Value(..)
+ , isSubtypeOf
 
 -- ** Dynamic use
 
@@ -150,15 +148,18 @@ 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
 -- >>> import Data.Text (Text)
 -- >>> import qualified Data.Text as T
--- >>> import Data.Void (Void)
+-- >>> import Data.Void (Void, vacuous)
 -- >>> import Prettyprinter (pretty)
 -- >>> import qualified Data.ByteString.Lazy.Char8 as BS
+-- >>> import Numeric.Natural
 -- >>> :set -XScopedTypeVariables
+-- >>> :set -XTypeApplications
 
 {- $haskell_types
 
@@ -169,7 +170,7 @@ The easiest way is to use this library is to use the canonical Haskell types. An
 >>> decode (encode ([True, False], Just 100)) == Right ([True, False], Just 100)
 True
 
-Here, no type annotations are needed, the library can infer them from the types of the Haskell values. You can see the Candid types used using `typeDesc` and `seqDesc`:
+Here, no type annotations are needed, the library can infer them from the types of the Haskell values. You can see the Candid types used using `seqDesc` (with `tieKnot`) for an argument sequence, or `typeDesc` for a single type:
 
 >>> :type +d ([True, False], Just 100)
 ([True, False], Just 100) :: ([Bool], Maybe Integer)
@@ -188,6 +189,8 @@ records directly:
 >>> pretty (typeDesc @(Rec ("bar" .== Maybe Integer .+ "foo" .== [Bool])))
 record {bar : opt int; foo : vec bool}
 
+NB: `typeDesc` cannot work with recursive types, but see `seqDesc` together with `tieKnot`.
+
 -}
 
 {- $own_type
@@ -375,7 +378,7 @@ If this encounters a Candid type definition, it will just inline them. This mean
 
 Sometimes one needs to interact with Candid in a dynamic way, without static type information.
 
-This library allows the parsing and pretty-printing of candid values. The binary value was copied from above:
+This library allows the parsing and pretty-printing of candid values:
 
 >>> import Data.Row
 >>> :set -XDataKinds -XTypeOperators
@@ -402,5 +405,18 @@ Right (#bar .== Just 100 .+ #foo .== [True,False])
 
 This function does not support the full textual format yet; in particular type annotations can only be used around number literals.
 
+Related to dynamic use is the ability to perform a subtype check, using 'isSubtypeOf' (but you have to set up the arguments correctly first):
+
+>>> isSubtypeOf (vacuous $ typeDesc @Natural) (vacuous $ typeDesc @Integer)
+Right ()
+>>> isSubtypeOf (vacuous $ typeDesc @Integer) (vacuous $ typeDesc @Natural)
+Left "Type int is not a subtype of nat"
+>>> isSubtypeOf (vacuous $ typeDesc @(Rec ("foo" .== [Bool]))) (vacuous $ typeDesc @(Rec ("bar" .== Maybe Integer .+ "foo" .== Maybe [Bool])))
+Right ()
+>>> isSubtypeOf (vacuous $ typeDesc @(Rec ("bar" .== Maybe Integer .+ "foo" .== Maybe [Bool]))) (vacuous $ typeDesc @(Rec ("foo" .== [Bool])))
+Left "Type opt vec bool is not a subtype of vec bool"
+>>> isSubtypeOf (vacuous $ typeDesc @(Rec ("bar" .== Integer))) (vacuous $ typeDesc @(Rec ("foo" .== Integer)))
+Left "Missing record field foo of type int"
+
 -}
 

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