Idris2/CHANGELOG.md

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 fromt the generated Scheme, using make bootstrap.

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.

Language extensions:

• %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)

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)

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.
  • In the run-time, reuse the old heap after garbage collection if it hasn't been resized, to avoid unnecessary system calls.

• 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

• 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

Changes since Idris 1

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