purescript

Enhancements

Scoped Type Variables

(#347, @paf31)

This feature allows type variables which are bound by a forall keyword to be used inside type annotations in the body of the function. For example, suppose we want to define a map function on a List type:

data List a = Nil | Cons a (List a)

map :: forall a b. (a -> b) -> List a -> List b
map f = go
  where
  go Nil = Nil
  go (Cons x xs) = Cons (f x) (map f xs) 

To give a type to go, we could previously use type wildcards:

go :: List _ -> List _

Now, we can refer to the types a and b inside the type of go, giving a more precise type:

go :: List a -> List b

Rows In Instance Contexts

(@paf31, @apsk)

This feature allows rows to appear on the left of a => in a type signature. For example, given a MonadEff class:

class MonadEff eff m where
  liftEff :: forall a. Eff eff a -> m a

we can now write the following function which works in any Monad supporting Trace actions:

logging :: forall m a eff. (Monad m, MonadEff (trace :: Trace | eff) m) => String -> m a -> m a
logging s action = do
  liftEff $ trace $ "Starting: " <> s
  a <- action
  liftEff $ trace $ "Done: " <> s
  return a

Improved let bindings in psci

(#782, @paf31)

Any declaration can now be used inside a let binding in psci. For example, we can define data types or foreign imports:

> let data Foo = Foo | Bar | Baz

> let foreign import foo :: Foo -> String

The general form of a let statement in psci now contains one or more declarations of any type, and these declarations simply get added to the current module.

As a bonus, polymorphic functions bound using let now work at multiple type instantiations in psci:

> let f x = x

> if f true then f "true" else f "False"
"true"

Markdown Support in psc-docs

(#802, @paf31)

Markdown can now be used for documentation purposes by using pipe characters to align content. For example:

-- | Create a copy of the array without its first element.
-- |
-- | Running time: `O(n)`, where `n` is the length of the array.
-- |
-- | This function is partial. Specifically, `tail []` is undefined.
tail :: forall a. [a] -> [a]

psc-docs will insert this markdown content verbatim into your generated documentation.

Bug Fixes

• Modules are rebuilt before a command is executed in psci, to avoid situations where compiled code becomes out-of-date (@paf31)
• @ is a valid operator name again (#815, @paf31)
• Reserved module names are now properly escaped (@garyb)

Breaking Changes

• The syntax of record getters was changed to _.prop (@garyb)

Enhancements

• The record part of a record updater can now be made into a wildcard, e.g. _ { foo = 1 } (@garyb)

• Extended infix expressions are now supported, (@paf31) e.g.

  [1, 2, 3] `zipWith (+)` [4, 5, 6]
  

Bug Fixes

• Newline issues were fixed in executables (@michaelficarra)

Enhancements

• Lightweight record constructors are now supported (@garyb):

  person :: Maybe String -> Maybe Number -> Maybe Address -> Maybe Person
  person = { name: _, age: _, location: _ } <$> name <*> age <*> location
  

• Field accessor sections are now supported (@garyb):

  getPersonName :: Maybe String
  getPersonName = (.name) <$> getPersonInfo
  

• Syntactic sugar has been introduced for object update functions:

  updateName :: Person -> String -> Person
  updateName person = person { name = _ }
  

• Operator sections are now supported (@garyb)

Bug Fixes

• Some command line options were fixed in psc-make (@paulyoung)
• Some module import errors were fixed (@garyb)
• A typechecker bug related to row synonyms was fixed (#795, @paf31)

Various small bug fixes.

• Fix some precedence issues in the code generator.
• Tighten the bounds on utf8-string.
• Fixed a bug in the typechecker.

Breaking Changes

Bug Fixes

• Case statement at end of Eff block not being executed. (#759, @paf31)
• A bug related to dead code elimination was fixed. (@garyb)
• Wildcards can now appear in row endings. (@RossMeikleham)

Enhancements

• There is a new "core functional representation", which will enable certain optimizations, and new features such as rewrite rules. (#710, @garyb)
• Record pattern matches now allow field names to be separated from binders using : instead of =, to match record construction (#760, @leighman)
• Some improvements needed for the Pursuit tool (@hdgarrood)
• The lexer was separated from the parser, and now supports explicit comments in the AST. Documentation generated by psc-docs now contains any inline comments which precede the corresponding declaration, and generated code preserves the same comments. (@paf31)
• PureScript now builds on GHC 7.6.* again. (@dylex)
• Proper names can now contain underscores. (@dylex)
• Several auto-completion improvements and fixes in PSCI. (@vkorablin)

Libraries

• The Prelude now contains a pureST function to run ST computations in a pure context. (@KMahoney)

Tools

• The Pursuit tool now runs on the community server, and integrates with Bower. Libraries can be added by submitting a pull request. (@hdgarrood)

Breaking Changes

• Command line options with multiplicity 1 now require an equals symbol, e.g.

  psc --main=Main --browser-namespace=PS
  

  The Grunt and Gulp plugins already support this format.

Enhancements

• Use optparse-applicative instead of cmdtheline (@anthoq88)

Libraries

• Move STArray out of Prelude. (@paf31)

Breaking Changes

• The pipe symbol is now a reserved operator.
• The operators in the Bits type class have been renamed.

Enhancements

• Fix build on GHC 7.6.* (@dylex)
• Relax indentation requirements (@paf31)

Breaking Changes

• The body of a guarded expression must now be indented past the guard. For example, this is valid:

positive n | n > 0 = true
positive _ = false

but this is not:

positive n | n > 0 
  = true
positive _ = false

New Features

• Type wildcards are now supported (#287, @paf31)

Enhancements

• Allow unquoted keywords as key names in record literals (#606, @michaelficarra)
• Import instances when referencing qualified values (#667, @garyb)
• Multiple guard clauses are now supported (#294, @paf31)
• Type check let declarations immediately in psci (#615, @garyb)

• Prevent psci and psc-make from rebuilding everything on every build #692

For more information on PureScript, see the purescript.org website.

Breaking Changes

• The Alternative type class hierarchy was refactored. See here.
• --runtime-type-checks has been removed. The recommended approach is to use purescript-foreign. (@garyb)
• The Unit type is now used in the Prelude and core libraries to represent values containing no data. (@garyb)
• The Prelude is no longer distributed as a separate file, but is embedded in the compiler executables. (@paf31)
• docgen is now called psc-docs.

New Features

• Newtypes are now supported using the newtype keyword. The runtime representation of a newtype is identical to that of the contained type. (@garyb)
• Multiline string literals are now supported via triple-quote syntax, making FFI declarations much neater. (@phadej)
• Kind signatures on types and type constructor arguments are now supported. (@paf31)

Enhancements

• The runFnN and mkFnN families of functions are now inlined by the optimizer, making interop with JavaScript functions of multiple arguments much simpler. (@paf31)
• Tail call optimization has been improved for functions using case expressions. (@paf31)
• Saturated calls to data constructors are now optimized. (@garyb)
• A new Renamer module now renames identifiers which shadow other names in scope, which greatly simplies code generation. (@garyb)
• psci now provides the following new options:
  • :b to browse a module (@ardumont)
  • :s to show current imports or modules (@ardumont)
  • :k to find the kind of a type constructor (@5outh)
• The approach to checking whether a name is initialized in the generated JavaScript was simplified (@paf31)
• The dependency on the PureScript_paths module has been removed, which makes distribution via binaries simpler. (@paf31)
• Nested if blocks now get optimized. (@garyb)
• Generated code for type class dictionaries was simplified. (@garyb, @dylex)
• The code generator now inserts the version of psc into the file as a comment. (@co-dh)
• () is now valid syntax, referring to the empty row. (@paf31)
• The type checker will now display multiple errors for type errors in the same binding group. (@paf31)
• Imports can now specify hidden names using import ... hiding ( ... ) (@andreypopp)

Bug Fixes

• Binding group errors in type class members are now caught at compile time. (@dylex)
• Some errors related to type checking rows with duplicate labels were fixed. (@paf31)
• Some issues with the calculation of binding groups were fixed. (@paf31)
• Error messages for invalid case declarations are now generated. (@natefaubion)
• Some issues related to module exports were fixed. (@garyb)
• psci now checks imports for validity. (@Bogdanp)

Libraries

• The Alternative type class hierarchy was refactored (@joneshf, @garyb)
• The exceptions library no longer supports throwing exceptions of any type.
• The following libraries have been moved to the core PureScript organisation: (@garyb)
  • purescript-transformers
  • purescript-free
  • purescript-const
  • purescript-identity
  • purescript-lazy
  • purescript-distributive
  • purescript-bifunctors
  • purescript-contravariant
  • purescript-profunctors
  • purescript-maps

Documentation

• The PureScript book is now available.
• The PureScript wiki is now the main resource for compiler and library documentation.

This incremental release is provided to provide bug fixes and features required to compile the latest core libraries.