<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
<html lang="en" style='--code-editor-font: var(--default-mono-font, "GitLab Mono"), JetBrains Mono, Menlo, DejaVu Sans Mono, Liberation Mono, Consolas, Ubuntu Mono, Courier New, andale mono, lucida console, monospace;'>
<head>
<meta content="text/html; charset=US-ASCII" http-equiv="Content-Type">
<title>
GitLab
</title>
<style data-premailer="ignore" type="text/css">
a { color: #1068bf; }
</style>
<style>img {
max-width: 100%; height: auto;
}
body {
font-size: .875rem;
}
body {
-webkit-text-shadow: rgba(255,255,255,.01) 0 0 1px;
}
body {
font-family: var(--default-regular-font, "GitLab Sans"),-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Noto Sans",Ubuntu,Cantarell,"Helvetica Neue",sans-serif,"Apple Color Emoji","Segoe UI Emoji","Segoe UI Symbol","Noto Color Emoji"; font-size: inherit;
}
</style>
</head>
<body style='font-size: inherit; -webkit-text-shadow: rgba(255,255,255,.01) 0 0 1px; font-family: var(--default-regular-font, "GitLab Sans"),-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Noto Sans",Ubuntu,Cantarell,"Helvetica Neue",sans-serif,"Apple Color Emoji","Segoe UI Emoji","Segoe UI Symbol","Noto Color Emoji";'>
<div class="content">
<h3 style="margin-top: 20px; margin-bottom: 10px;">
Vladislav Zavialov pushed to branch wip/int-index/wildcard-binders at <a href="https://gitlab.haskell.org/ghc/ghc">Glasgow Haskell Compiler / GHC</a>
</h3>
<h4 style="margin-top: 10px; margin-bottom: 10px;">
Commits:
</h4>
<ul>
<li>
<strong style="font-weight: 600;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/f219d5cb024bb1903894daf382aa483ec2f70bc6">f219d5cb</a></strong>
<div>
<span> by Vladislav Zavialov </span> <i> at 2024-08-29T22:27:32+00:00 </i>
</div>
<pre class="commit-message" style='white-space: pre-wrap; display: block; font-size: 14px; color: #333238; position: relative; font-family: var(--default-mono-font, "GitLab Mono"),"JetBrains Mono","Menlo","DejaVu Sans Mono","Liberation Mono","Consolas","Ubuntu Mono","Courier New","andale mono","lucida console",monospace; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; border-radius: 2px; margin: 0; padding: 8px 12px; border: 1px solid #dcdcde;'>Wildcard binders in type declarations (#23501)
Add support for wildcard binders in type declarations:
type Const a b = a -- BEFORE: the `b` had to be named
-- even if unused on the RHS
type Const a _ = a -- AFTER: the compiler accepts
-- a wildcard binder `_`
The new feature is part of GHC Proposal #425 "Invisible binders
in type declarations", and more specifically its amendment #641.
Just like a named binder, a wildcard binder `_` may be:
* plain: _
* kinded: (_ :: k -> Type)
* invisible, plain: @_
* invisible, kinded: @(_ :: k -> Type)
Those new forms of binders are allowed to occur on the LHSs of
data, newtype, type, class, and type/data family declarations:
data D _ = ...
newtype N _ = ...
type T _ = ...
class C _ where ...
type family F _
data family DF _
(Test case: testsuite/tests/typecheck/should_compile/T23501a.hs)
However, we choose to reject them in forall telescopes and
type family result variable binders (the latter being part
of the TypeFamilyDependencies extension):
type family Fd a = _ -- disallowed (WildcardBndrInTyFamResultVar)
fn :: forall _. Int -- disallowed (WildcardBndrInForallTelescope)
(Test case: testsuite/tests/rename/should_fail/T23501_fail.hs)
See the new Notes:
* Note [Type variable binders]
* Note [Wildcard binders in disallowed contexts]
To accommodate the new forms of binders, HsTyVarBndr was changed
as follows (demonstrated without x-fields for clarity)
-- BEFORE (ignoring x-fields and locations)
data HsTyVarBndr flag
= UserTyVar flag Name
| KindedTyVar flag Name HsKind
-- AFTER (ignoring x-fields and locations)
data HsTyVarBndr flag = HsTvb flag HsBndrVar HsBndrKind
data HsBndrVar = HsBndrVar Name | HsBndrWildCard
data HsBndrKind = HsBndrNoKind | HsBndrKind LHsKind
The rest of the patch is downstream from this change.
To avoid a breaking change to the TH AST, we generate fresh
names to replace wildcard binders instead of adding a dedicated
representation for them (as discussed in #641).
And to put a cherry on top of the cake, we now allow wildcards in
kind-polymorphic type variable binders in constructor patterns,
see Note [Type patterns: binders and unifiers] and the tyPatToBndr
function in GHC.Tc.Gen.HsType; example:
fn (MkT @(_ :: forall k. k -> Type) _ _) = ...
(Test case: testsuite/tests/typecheck/should_compile/T23501b.hs)
</pre>
</li>
</ul>
<h4 style="margin-top: 10px; margin-bottom: 10px;">
30 changed files:
</h4>
<ul>
<li class="file-stats">
<a href="#75bfcd03f3ba9315d33104fcb0424c6bfeb4e334">
compiler/GHC/Hs/Decls.hs
</a>
</li>
<li class="file-stats">
<a href="#9f00edfedb0f969865b049a78de3866545b4a60b">
compiler/GHC/Hs/Instances.hs
</a>
</li>
<li class="file-stats">
<a href="#018be522bc4813b147a1525e4f96a7a493207d96">
compiler/GHC/Hs/Type.hs
</a>
</li>
<li class="file-stats">
<a href="#3c19c0be465f9a28d7b69f89c55648080fcc37eb">
compiler/GHC/HsToCore/Quote.hs
</a>
</li>
<li class="file-stats">
<a href="#649144a78135a23cabfc90dd83c4aabf448eb6ab">
compiler/GHC/Iface/Ext/Ast.hs
</a>
</li>
<li class="file-stats">
<a href="#bf951467d4a9aa443cb109cb4c84a2891945649b">
compiler/GHC/Parser.y
</a>
</li>
<li class="file-stats">
<a href="#446cb12ca6cefaf1c6eb79b7db643632744263c7">
compiler/GHC/Parser/PostProcess.hs
</a>
</li>
<li class="file-stats">
<a href="#892acbb198a9095c917740d3c1297b56df4e3b7e">
compiler/GHC/Rename/HsType.hs
</a>
</li>
<li class="file-stats">
<a href="#7dd1cd0f6f2164a14c83d9aa564dd32bc30e447a">
compiler/GHC/Rename/Module.hs
</a>
</li>
<li class="file-stats">
<a href="#3aa56839e36b2219f9ad54f5646ef3005da9c672">
compiler/GHC/Tc/Deriv/Generate.hs
</a>
</li>
<li class="file-stats">
<a href="#1dd9c7a6bbc222c976a6ec1c4b772232ae60f7e5">
compiler/GHC/Tc/Errors/Ppr.hs
</a>
</li>
<li class="file-stats">
<a href="#cdba811872892f235fe7059df1a6c538fba60816">
compiler/GHC/Tc/Errors/Types.hs
</a>
</li>
<li class="file-stats">
<a href="#9355bef855426caf5f526925edf351b20f9a86c4">
compiler/GHC/Tc/Gen/HsType.hs
</a>
</li>
<li class="file-stats">
<a href="#eade747fa0a15693c67617629e286714fce958e4">
compiler/GHC/Tc/Gen/Sig.hs
</a>
</li>
<li class="file-stats">
<a href="#83d23a46bb6cdc8b1edc16f1fd2c8f5c53e2c9ca">
compiler/GHC/Tc/TyCl.hs
</a>
</li>
<li class="file-stats">
<a href="#2eac51f9871ca0c0698aa1fc7f79c05ef8fc4a49">
compiler/GHC/ThToHs.hs
</a>
</li>
<li class="file-stats">
<a href="#55fd4da29695073f23c02f21476e753eb7c467b4">
compiler/Language/Haskell/Syntax/Extension.hs
</a>
</li>
<li class="file-stats">
<a href="#ef5ad6f4dfc8fa107eace213eecba4bc1014ca57">
compiler/Language/Haskell/Syntax/Type.hs
</a>
</li>
<li class="file-stats">
<a href="#002ac3d1b67a64e8aea422a8712ff6d42458235a">
testsuite/tests/haddock/should_compile_flag_haddock/T17544.stderr
</a>
</li>
<li class="file-stats">
<a href="#d0624eb2a076bdbe3f842da55a5579e29c6cabe2">
testsuite/tests/haddock/should_compile_flag_haddock/T17544_kw.stderr
</a>
</li>
<li class="file-stats">
<a href="#e6a699bed61e0c8d8109f383d714115200dd37b4">
testsuite/tests/parser/should_compile/DumpParsedAst.stderr
</a>
</li>
<li class="file-stats">
<a href="#338eb1c1a80bcdbcecf4018a1808183f4305c65b">
testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
</a>
</li>
<li class="file-stats">
<a href="#4afdc3da79634c15b8fbfb6e765dc12ea54bece7">
testsuite/tests/parser/should_compile/DumpSemis.stderr
</a>
</li>
<li class="file-stats">
<a href="#ee24e3a743c7969d4a3cfdec1d00511d39dad123">
testsuite/tests/parser/should_compile/KindSigs.stderr
</a>
</li>
<li class="file-stats">
<a href="#80cef6ecfd8cfb192e74919082dee97bf5a70067">
testsuite/tests/parser/should_compile/T15323.stderr
</a>
</li>
<li class="file-stats">
<a href="#7bf6b8534c3526853866ce7ffe6017cfe65b7bf8">
testsuite/tests/parser/should_compile/T20452.stderr
</a>
</li>
<li class="file-stats">
<a href="#59c2b90494aa3229d0ed90ba9abc1a63db2c9457">
testsuite/tests/partial-sigs/should_fail/WildcardInTypeSynonymLHS.hs
</a>
</li>
<li class="file-stats">
<a href="#2fbe4fdeb2e819964a44ff31a86cd14809badefd">
testsuite/tests/partial-sigs/should_fail/WildcardInTypeSynonymLHS.stderr
</a>
</li>
<li class="file-stats">
<a href="#8cb35be8f13ce47421a8f834d7262e0459fb7e5a">
testsuite/tests/printer/Test24533.stdout
</a>
</li>
<li class="file-stats">
<a href="#e544a7c3ac14b8020722810747213ef4d4db5dca">
<span class="new-file">
+
testsuite/tests/rename/should_fail/T23501_fail.hs
</span>
</a>
</li>
</ul>
<h5 style="margin-top: 10px; margin-bottom: 10px; font-size: .875rem;">
The diff was not included because it is too large.
</h5>
</div>
<div class="footer" style="margin-top: 10px;">
<p style="font-size: small; color: #737278;">
—
<br>
<a href="https://gitlab.haskell.org/ghc/ghc/-/commit/f219d5cb024bb1903894daf382aa483ec2f70bc6">View it on GitLab</a>.
<br>
You're receiving this email because of your account on <a target="_blank" rel="noopener noreferrer" href="https://gitlab.haskell.org">gitlab.haskell.org</a>. <a href="https://gitlab.haskell.org/-/profile/notifications" target="_blank" rel="noopener noreferrer" class="mng-notif-link">Manage all notifications</a> · <a href="https://gitlab.haskell.org/help" target="_blank" rel="noopener noreferrer" class="help-link">Help</a>
<script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","action":{"@type":"ViewAction","name":"View Commit","url":"https://gitlab.haskell.org/ghc/ghc/-/commit/f219d5cb024bb1903894daf382aa483ec2f70bc6"}}</script>
</p>
</div>
</body>
</html>