1 Unicode Ellipsis

1.1 Motivation

We already have beautiful Unicode make-up for all reserved symbols. And they look great!

But no, not for all. The poor ellipsis .. is left without. It wants to look like this: ….

1.2 Proposed Change Specification

When the UnicodeSyntax extension is enabled:

1. Make … accepted wherever .. is accepted.

2. Allow … in situations like [False…] where ASCII syntax [False..] would be a parse error. (This is automatically the case with the patch proposed below.) (Thanks to Jakob Brünker forpointing this out.)

1.3 Examples

{-# language UnicodeSyntax #-}
{-# language RecordWildCards #-}

module X where

import Prelude (Bool (…))

data Record = Record {value ∷ Bool}

function ∷ Record → Bool
function Record {…} = value

booleans ∷ [Bool]
booleans = [False…]

1.4 Effect and Interactions

Ellipsis gets its beautiful Unicode make-up.

1.5 Costs and Drawbacks

There are no costs and no drawbacks.

1.6 Alternatives

There are no alternatives.

1.7 Unresolved Questions

There are no unresolved questions.

1.8 Implementation Plan

Apply this patch:

diff --git a/compiler/GHC/Parser/Lexer.x b/compiler/GHC/Parser/Lexer.x
index d74d17be8f..4135372d31 100644
--- a/compiler/GHC/Parser/Lexer.x
+++ b/compiler/GHC/Parser/Lexer.x
@@ -1063,6 +1063,7 @@ reservedSymsFM = listToUFM $
        ,("-<<", ITLarrowtail NormalSyntax,  NormalSyntax,  xbit ArrowsBit)
        ,(">>-", ITRarrowtail NormalSyntax,  NormalSyntax,  xbit ArrowsBit)

+       , ("…",  ITdotdot,                   UnicodeSyntax,  0 )
        ,("∷",   ITdcolon UnicodeSyntax,     UnicodeSyntax, 0 )
        ,("⇒",   ITdarrow UnicodeSyntax,     UnicodeSyntax, 0 )
        ,("∀",   ITforall UnicodeSyntax,     UnicodeSyntax, 0 )

1.9 Endorsements

There are no endorsements.