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Idris2/CHANGELOG.md
Edwin Brady 3a6614b227 Look at intermediate results in program search 
This has involved quite a bit of reorganisation and some improvements in
resugaring so that the results look nice. In summary:

* Expression search now gives back a RawImp rather than a checked term,
  which allows it to include case expressions
* Case with one pattern is resugared to a destructuring let
* Some name generation issues address in function generation

We look at intermediate results for local variables which are functions
that return a concrete type, or recursive calls that return a single
constructor type. In these cases, we:

* let bind the local variable/recursive call
* generate a new definition for the scope, as a 'case' function

When we recursively generate the definition, it's a bit more restricted
so as not to explode the search space. We only take the first result, we
only look one constructor deep, and we go right to left on variable
splitting so only deconstruct the name we've just added.
2020-08-04 12:51:57 +01:00

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Changes since Idris 2 v0.2.0

Language changes:

  • Bits8, Bits16, Bits32 and Bits64 primitive types added, with:
    • Num, Eq, Ord and Show implementations.
    • Casts from Integer, for literals
    • Casts to Int (except Bits64 which might not fit), Integer and String
    • Passed to C FFI as unsigned
    • Primitives added in Data.Buffer
  • Elaborator reflection and quoting terms
    • Requires extension %language ElabReflection
    • API defined in Language.Reflection, including functions for getting types of global names, constructors of data types, and adding new top level declarations
    • Implemented %macro function flag, to remove the syntactic noise of invoking elaborator scripts. This means the function must always be fully applied, and is run under %runElab
  • Add import X as Y
    • This imports the module X, adding aliases for the definitions in namespace Y, so they can be referred to as Y.
  • do notation can now be qualified with a namespace
    • MyDo.do opens a do block where the >>= operator used is MyDo.(>>=)

Library changes:

  • IO operations in the prelude and base libraries now use the HasIO interface, rather than using IO directly.
  • Experimental Data.Linear.Array added to contrib, supporting mutable linear arrays with constant time read/write, convertible to immutable arrays with constant time read.
    • Anything in Data.Linear in contrib, just like the rest of contrib, should be considered experimental with the API able to change at any time! Further experiments in Data.Linear are welcome :).
  • Experimental Control.Linear.LIO added to contrib, supporting computations which track the multiplicities of their return values, which allows linear resources to be tracked.
  • Added Control.Monad.ST, for update in-place via STRef (which is like IORef, but can escape from IO). Also added Data.Ref which provides an interface to both IORef and STRef.
  • Added Control.ANSI in contrib, for usage of ANSI escape codes for text styling and cursor/screen control in terminals.

Command-line options changes:

  • Removed --ide-mode-socket-with option. --ide-mode-socket now accepts an optional host:port argument.
  • Added options to override source directory, build directory and output directory: --source-dir, --build-dir, --output-dir.
    • These options are also available as fields in the package description: sourcedir, builddir, outputdir.

Compiler changes:

  • It is now possible to create new backends with minimal overhead. Idris.Driver exposes the function mainWithCodegens that takes a list of codegens. The feature in documented here.
  • New code generators node and javascript.

REPL/IDE mode changes:

  • Implemented :module command, to load a module during a REPL session.
  • Implemented :doc, which displays documentation for a name.
  • Implemented :browse, which lists the names exported by a namespace.
  • Added :psnext, which continues the previous proof search, looking for the next type correct expression
    • Correspondingly, added the IDE mode command proof-search-next (which takes no arguments)
  • Added :gdnext, which continues the previous program search, looking for the next type correct implementation
    • Correspondingly, added the IDE mode command generate-def-next (which takes no arguments)
  • Improved program search to allow deconstructing intermediate values, and in simple cases, the result of recursive calls.

Changes since Idris 2 v0.1.0

The implementation is now self-hosted. To initialise the build, either use the bootstrapping version of Idris2 or build from the generated Scheme, using make bootstrap.

Language changes:

  • total, covering and partial flags on functions now have an effect.
  • %default <totality status> has been implemented. By default, functions must be at least covering
    • That is, %default covering is the default status.
  • Fields of records can be accessed (and updated) using the dot syntax, such as r.field1.field2 or record { field1.field2 = 42 }. For details, see https://idris2.readthedocs.io/en/latest/reference/records.html
  • New function flag %tcinline which means that the function should be inlined for the purposes of totality checking (but otherwise not inlined). This can be used as a hint for totality checking, to make the checker look inside functions that it otherwise might not.
  • %transform directive, for declaring transformation rules on runtime expressions. Transformation rules are automatically added for top level implementations of interfaces.
  • A %spec flag on functions which allows arguments to be marked for partial evaluation, following the rules from "Scrapping Your Inefficient Engine" (ICFP 2010, Brady & Hammond)
  • To improve error messages, one can use with NS.name <term> or with [NS.name1, NS.name2, ...] <term> to disable disambiguation for the given names in <term>. Example: with MyNS.(>>=) do ....

Library additions:

  • Additional file management operations in base
  • New module in base for time (System.Clock)
  • New modules in contrib for JSON (Language.JSON.*); random numbers (System.Random)

Compiler updates:

  • Data types with a single constructor, with a single unerased arguments, are translated to just that argument, to save repeated packing and unpacking. (c.f. newtype in Haskell)
    • A data type can opt out of this behaviour by specifying noNewtype in its options list. noNewtype allows code generators to apply special handling to the generated constructor/deconstructor, for a newtype-like data type, that would otherwise be optimised away.
  • 0-multiplicity constructor arguments are now properly erased, not just given a placeholder null value.

Other improvements:

  • Various performance improvements in the typechecker:
    • Noting which metavariables are blocking unification constraints, so that they only get retried if those metavariables make progress.
    • Evaluating fromInteger at compile time.
  • Extend Idris2's literate mode to support reading Markdown and OrgMode files. For more details see: https://idris2.readthedocs.io/en/latest/reference/literate.html

Changes since Idris 1

Everything :). For full details, see: https://idris2.readthedocs.io/en/latest/updates/updates.html