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refactor README and installation instructions
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,119 +1,38 @@ | ||
| Idris 2 | ||
| ======= | ||
| # Idris 2 | ||
|
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||
| [](https://idris2.readthedocs.io/en/latest/?badge=latest) | ||
| [](https://github.com/idris-lang/Idris2/actions/workflows/ci-idris2-and-libs.yml?query=branch%3Amain) | ||
|
|
||
| [Idris 2](https://idris-lang.org/) is a purely functional programming language | ||
| with first class types. | ||
|
|
||
| For full installation instructions, see [INSTALL.md](INSTALL.md). Briefly, if | ||
| you have Chez Scheme installed, with the executable name `chez`, type: | ||
| For installation instructions, see [INSTALL.md](INSTALL.md). | ||
|
|
||
| * `make bootstrap SCHEME=chez` | ||
| * `make install` | ||
| The [wiki](https://github.com/idris-lang/Idris2/wiki) lists a number of useful | ||
| resources, in particular | ||
|
|
||
| You may need to change `chez` to be the local name of your Chez Scheme. This | ||
| is often one of `scheme`, `chezscheme` or `chezscheme9.5` (depending on the | ||
| version). On a modern desktop machine, this process (including tests) | ||
| should take less than 5 minutes. | ||
| + [What's changed since Idris 1](https://idris2.readthedocs.io/en/latest/updates/updates.html) | ||
| + [Resources for learning Idris](https://github.com/idris-lang/Idris2/wiki/Resources), | ||
| including [official talks](https://github.com/idris-lang/Idris2/wiki/Resources#official-talks) | ||
| that showcase its capabilities | ||
| + [Editor support](https://github.com/idris-lang/Idris2/wiki/Editor-Support) | ||
|
|
||
| Idris 2 is mostly backward compatible with Idris 1, with some minor exceptions. | ||
| The most notable user visible differences, which might cause Idris 1 programs | ||
| to fail to type check, are: | ||
| ## Things still missing | ||
|
|
||
| + Unbound implicit arguments are always erased, so it is a type error to | ||
| attempt to pattern match on one. | ||
| + Simplified resolution of ambiguous names, which might mean you need to | ||
| explicitly disambiguate more often. As a general rule, Idris 2 will be able | ||
| to disambiguate between names which have different concrete return types | ||
| (such as data constructors), or which have different concrete argument | ||
| types (such as record projections). It may struggle to resolve ambiguities | ||
| if one name requires an interface to be resolved. | ||
| + The `cong` function now takes its congruence explicitly as its first argument. | ||
| + Minor differences in the meaning of export modifiers `private`, `export`, | ||
| and `public export`, which now refer to visibility of names from other | ||
| *namespaces* rather than visibility from other *files*. | ||
| + Module names must match the filename in which they are defined (unless | ||
| the module's name is "Main"). | ||
| + Anything which uses a `%language` pragma in Idris 1 is likely to be different. | ||
| Notably, elaborator reflection will exist, but most likely in a slightly | ||
| different form because the internal details of the elaborator are different. | ||
| + The `Prelude` is much smaller (and easier to replace with an alternative). | ||
| Command-line option `--no-prelude` can be used to not implicitly import `Prelude`. | ||
| + `let x = val in e` no longer computes with `x` in `e`, instead being | ||
| essentially equivalent to `(\x => e) val`. This is to make the | ||
| behaviour of `let` consistent in the presence of `case` and `with` (where | ||
| it is hard to push the computation inside the `case`/`with` efficiently). | ||
| Instead, you can define functions locally with `let`, which do have | ||
| computational force, as follows: | ||
| + Cumulativity (currently `Type : Type`. Bear that in mind when you think | ||
| you've proved something) | ||
| + `rewrite` doesn't yet work on dependent types | ||
|
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||
| let x : ? | ||
| x = val in | ||
| e | ||
| ## Contributions wanted | ||
|
|
||
| Watch this space for more details and the rationale for the changes, as I | ||
| get around to writing it... | ||
| If you want to learn more about Idris, contributing to the compiler could be | ||
| one way to do so. The [contribution guidelines](CONTRIBUTING.md) outline | ||
| the process. Having read that, choose a [good first issue][1] or have a look at | ||
| the [contributions wanted][2] for something more involved. This [map][3] should | ||
| help you find your way around the source code. See [the wiki page][4] | ||
| for more details. | ||
|
|
||
| Summary of new features: | ||
|
|
||
| + A core language based on "Quantitative Type Theory" which allows explicit | ||
| annotation of erased types, and linear types. | ||
| + `let` bindings are now more expressive, and can be used to define pattern | ||
| matching functions locally. | ||
| + Names which are in scope in a type are also always in scope in the body of | ||
| the corresponding definition. | ||
| + Better inference. Holes are global to a source file, rather than local to | ||
| a definition, meaning that some holes can be left in function types to be | ||
| inferred by the type checker. This also gives better inference for the types | ||
| of `case` expressions, and means fewer annotations are needed in interface | ||
| declarations. | ||
| + Better type checker implementation which minimises the need for compile | ||
| time evaluation. | ||
| + New Chez Scheme based backend which both compiles and runs faster than the | ||
| default Idris 1 backend. (Also, optionally, Racket and Gambit can be used | ||
| as targets). | ||
| + Everything works faster :). | ||
|
|
||
| A significant change in the implementation is that there is an intermediate | ||
| language `TTImp`, which is essentially a desugared Idris, and is cleanly | ||
| separated from the high level language which means it is potentially usable | ||
| as a core language for other high level syntaxes. | ||
|
|
||
| JavaScript | ||
| ---------- | ||
| The JavaScript codegen uses the new BigInt, hence Node.js 10.4 or higher is required. | ||
|
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||
| Editor Plugins | ||
| -------------- | ||
| The [wiki lists the current plugins available for common text editors]( | ||
| https://github.com/idris-lang/Idris2/wiki/Editor-Support) | ||
| and their features. | ||
|
|
||
| Things still missing | ||
| -------------------- | ||
|
|
||
| + Cumulativity (so we currently have Type : Type! Bear that in mind when you | ||
| think you've proved something :)) | ||
| + 'rewrite' doesn't yet work on dependent types | ||
|
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||
| Contributions wanted | ||
| ------------------- | ||
|
|
||
| + [Contribution guidelines](CONTRIBUTING.md) | ||
| + [Good first issues](https://github.com/idris-lang/Idris2/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22) | ||
| + [Contributors wanted](https://github.com/idris-lang/Idris2/wiki/What-Contributions-are-Needed) | ||
|
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||
| If you want to learn about Idris more, contributing to the compiler could be one | ||
| 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 | ||
| ----- | ||
|
|
||
| [](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)") | ||
| [1]: <https://github.com/idris-lang/Idris2/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22> | ||
| [2]: <https://github.com/idris-lang/Idris2/wiki/What-Contributions-are-Needed> | ||
| [3]: <https://github.com/idris-lang/Idris2/wiki/Map-of-the-Source-Code> | ||
| [4]: <https://github.com/idris-lang/Idris2/wiki/Getting-Started-with-Compiler-Development> |
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