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purescript v0.10.1 Release Notes

Release Date: 2016-10-02 // over 7 years ago

  • 💥 Breaking Changes

    🛠 The new functional dependencies feature fixes type inference in some cases involving multi-parameter type classes. However, due to a bug in the compiler, some of those expressions were previously type checking where they should not have. As a result, it is necessary to add functional dependencies to some classes in order to make previous code type-check in some cases. Known examples are:

    • MonadEff and MonadAff
    • 💅 MonadState, MonadReader, and the rest of the MTL-style classes in transformers

    🆕 New Features

    Data.Newtype Deriving

    (@garyb)

    It is now possible to derive the Newtype class for any data declaration which is a newtype, using the existing deriving instance syntax:

    newtype Test = Test String

derive instance newtypeTest :: Newtype Test _

    Note that the second type argument should be specified as a wildcard, and will be inferred.

    ➕ Added type level string functions

    (@FrigoEU)

    🏗 The Prim module now defines the TypeString and TypeConcat type constructors, which can be used to build more descriptive error messages which can depend on types, using the Fail constraint:

    instance cannotShowFunctions
    :: Fail ("Function type " <> TypeString (a -> b) <> " cannot be shown.")
    => Show (a -> b) where
  show _ = "unreachable"

infixl 6 type TypeConcat as <>

    --dump-corefn

    (@rightfold)

    👍 The compiler now supports the --dump-corefn option, which causes the functional core to be dumped in output/**/corefn.json. This should be useful for implementing new backends which interpret the functional core.

    🆕 Newtype Deriving

    (@paf31)

    It is now possible to derive type class instances for newtypes, by reusing the instance for the underlying type:

    newtype X = X String

derive newtype instance showX :: Show X

    Note that it is possible to derive instances for multi-parameter type classes, but the newtype must only appear as the last type argument.

    👍 Allow anonymous accessor chains (_.a.b)

    (@rvion)

    Anonymous record accessor syntax has been extended to work with chains of one or more accessors:

    getBaz = _.foo.bar.baz

    Functional Dependencies (@paf31)

    👍 The type class solver now supports functional dependencies. A multi-parameter type class can define dependencies between its type arguments by using the -> operator:

    class Stream el s | s -> el where
  cons :: el -> (Unit -> s) -> s
  uncons :: s -> { head :: el, tail :: s }

    Here, the s and el type arguments are related by a single functional dependency, which ensures that there is at most one instance for any given type s. Alternatively, the type s determines the type el, i.e. there is an implicit function from types s to types el. This information can be used by the solver to infer types where it was previously not possible.

    👀 See the following examples for more information:

    ✨ Enhancements

    • Return qualifier from explicit/hiding imports (@nwolverson)
    • 👌 Verify entry points exist in psc-bundle (@kRITZCREEK)
    • 👌 Improved error messages for record subsumption (@FrigoEU)

    psc-ide

    • Resolve types/kinds for operators (@kRITZCREEK)
    • Unify Completion Commands (@kRITZCREEK)
    • 📜 Parse type annotations from source files (@kRITZCREEK)
    • ⚡️ Update pursuit JSON parsing (@nwolverson)
    • ✂ Remove a pursuit workaround (@kRITZCREEK)
    • ➕ Add a suggestion to the UnusedDctorImport warning (@FrigoEU)
    • Return JSON errors for cycles in module dependencies (@kRITZCREEK)

    🐛 Bug Fixes

    • 🛠 Fix usage detection for operators (@garyb)
    • 🛠 Fix handling of duplicate module imports in JS codegen (@garyb)
    • 🛠 Fix a small bug in the type pretty-printer (@paf31)
    • 🛠 Fix function application judgment (@paf31)
    • 🛠 Fix inlining for $ and # operators (@garyb)
    • 🛠 Fix everywhereOnTypesTopDown (@ianbollinger)
    • 🛠 Fix unification of string literals (@paf31)

    Infrastructure

    • 👌 Support aeson-1.0 (@phadej)
    • 👌 Support http-client-0.5 (@phadej)
    • Safer installation from source in INSTALL.md (@hdgarrood)

    Implementation

    • 🛠 Fix most HLint warnings (@ianbollinger)
    • 🛠 Fixing imports (@charleso)
    • Export desugarDecl from Sugar.ObjectWildcards (@rvion)
    • ✂ Remove legacy ObjectGetter and update doc (@rvion)