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3ee965e30d
We had a lot of things missing here, and the contributing guidelines were extremely out of date and reflected the state when I first made the Idris 2 repo public. I've updated both to reflect the current state of the way we work, and to give better guidelines about what will be most helpful.
119 lines
6.0 KiB
Markdown
119 lines
6.0 KiB
Markdown
Idris 2
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=======
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[](https://idris2.readthedocs.io/en/latest/?badge=latest)
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[](https://github.com/idris-lang/Idris2/actions/workflows/ci-idris2.yml)
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[Idris 2](https://idris-lang.org/) is a purely functional programming language
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with first class types.
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For full installation instructions, see [INSTALL.md](INSTALL.md). Briefly, if
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you have Chez Scheme installed, with the executable name `chez`, type:
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* `make bootstrap SCHEME=chez`
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* `make install`
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You may need to change `chez` to be the local name of your Chez Scheme. This
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is often one of `scheme`, `chezscheme` or `chezscheme9.5` (depending on the
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version). On a modern desktop machine, this process (including tests)
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should take less than 5 minutes.
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Idris 2 is mostly backwards compatible with Idris 1, with some minor
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exceptions. The most notable user visible differences, which might cause Idris
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1 programs to fail to type check, are:
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+ Unbound implicit arguments are always erased, so it is a type error to
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attempt to pattern match on one.
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+ Simplified resolution of ambiguous names, which might mean you need to
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explicitly disambiguate more often. As a general rule, Idris 2 will be able
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to disambiguate between names which have different concrete return types
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(such as data constructors), or which have different concrete argument
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types (such as record projections). It may struggle to resolve ambiguities
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if one name requires an interface to be resolved.
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+ The `cong` function now takes its congruence explicitly as its first argument.
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+ Minor differences in the meaning of export modifiers `private`, `export`,
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and `public export`, which now refer to visibility of names from other
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*namespaces* rather than visibility from other *files*.
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+ Module names must match the filename in which they are defined (unless
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the module's name is "Main").
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+ Anything which uses a `%language` pragma in Idris 1 is likely to be different.
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Notably, elaborator reflection will exist, but most likely in a slightly
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different form because the internal details of the elaborator are different.
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+ The `Prelude` is much smaller (and easier to replace with an alternative).
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Command-line option `--no-prelude` can be used to not implicitly import `Prelude`.
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+ `let x = val in e` no longer computes with `x` in `e`, instead being
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essentially equivalent to `(\x => e) val`. This is to make the
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behaviour of `let` consistent in the presence of `case` and `with` (where
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it is hard to push the computation inside the `case`/`with` efficiently).
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Instead, you can define functions locally with `let`, which do have
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computational force, as follows:
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let x : ?
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x = val in
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e
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Watch this space for more details and the rationale for the changes, as I
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get around to writing it...
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Summary of new features:
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+ A core language based on "Quantitative Type Theory" which allows explicit
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annotation of erased types, and linear types.
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+ `let` bindings are now more expressive, and can be used to define pattern
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matching functions locally.
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+ Names which are in scope in a type are also always in scope in the body of
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the corresponding definition.
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+ Better inference. Holes are global to a source file, rather than local to
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a definition, meaning that some holes can be left in function types to be
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inferred by the type checker. This also gives better inference for the types
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of `case` expressions, and means fewer annotations are needed in interface
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declarations.
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+ Better type checker implementation which minimises the need for compile
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time evaluation.
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+ New Chez Scheme based back end which both compiles and runs faster than the
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default Idris 1 back end. (Also, optionally, Racket and Gambit can be used
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as targets).
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+ Everything works faster :).
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A significant change in the implementation is that there is an intermediate
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language `TTImp`, which is essentially a desugared Idris, and is cleanly
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separated from the high level language which means it is potentially usable
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as a core language for other high level syntaxes.
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Javascript
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----------
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The javascript codegen uses the new BigInt, hence nodejs 10.4 or higher is required.
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Editor Plugins
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--------------
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The [wiki](https://github.com/idris-lang/Idris2/wiki/The-Idris-editor-experience)
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lists the current plugins available for common text editors and their features.
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Things still missing
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--------------------
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+ Cumulativity (so we currently have Type : Type! Bear that in mind when you
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think you've proved something :))
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+ 'rewrite' doesn't yet work on dependent types
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Contributions wanted
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-------------------
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+ [Contribution guidelines](CONTRIBUTING.md)
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+ [Good first issues](https://github.com/idris-lang/Idris2/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22)
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+ [Contributors wanted](https://github.com/idris-lang/Idris2/wiki/Contributions-wanted)
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If you want to learn about Idris more, contributing to the compiler could be one
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way to do so. Just select one good first issue and ask about it on the [Discord](https://discord.gg/UX68fDs2jc) channel.
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Talks
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-----
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[](https://www.youtube.com/watch?v=nbClauMCeds "Edwin Brady Tells Us What's New in Idris 2 (Berlin Functional Programming Group)")
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[](https://www.youtube.com/watch?v=h9YAOaBWuIk "Scheme Workshop Keynote (ACM SIGPLAN)")
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[](https://www.youtube.com/watch?v=DRq2NgeFcO0 "Idris 2 - Type-driven Development of Idris (Curry On - London 2019)")
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[](https://www.youtube.com/watch?v=mOtKD7ml0NU "Idris 2: Type-driven Development of Idris (Code Mesh LDN 18)")
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