runtime(haskell): allow spaces in backticked operators in syntax script

This formatting (although rare) is actually accepted by GHC, but vim
does not highlight it. This patch adds the simplest possible regex to
support the behavior.

Inconveniently, this might trigger weird formatting on lines that
contain errors, e.g. if the first backtick is removed from:

    a `b` c `d` e

then `c` is going to be marked as an operator, which seems weird but is
valid.

closes: #18776

Signed-off-by: Mirek Kratochvil <[email protected]>
Signed-off-by: Christian Brabandt <[email protected]>

Author: exaexa

runtime/syntax/haskell.vim

@@ -2,6 +2,7 @@
 " Language:		Haskell
 " Maintainer:		Haskell Cafe mailinglist <[email protected]>
 " Last Change:		2024 Mar 28 by Enrico Maria De Angelis <[email protected]>
+"			2025 Nov 20 by Vim Project: Allow spaces in backticks #18776
 " Original Author:	John Williams <[email protected]>
 "
 " Thanks to Ryan Crumley for suggestions and John Meacham for
@@ -46,8 +47,8 @@ syn match VarId "\(\<[A-Z][a-zA-Z0-9_']*\.\)*\<[a-z][a-zA-Z0-9_']*\>" contains=@
 " others are variables (e.g. functions).
 syn match hsVarSym "\(\<[A-Z][a-zA-Z0-9_']*\.\)\=[-!#$%&\*\+/<=>\?@\\^|~.][-!#$%&\*\+/<=>\?@\\^|~:.]*"
 syn match hsConSym "\(\<[A-Z][a-zA-Z0-9_']*\.\)\=:[-!#$%&\*\+./<=>\?@\\^|~:]*"
-syn match hsVarSym "`\(\<[A-Z][a-zA-Z0-9_']*\.\)\=[a-z][a-zA-Z0-9_']*`"
-syn match hsConSym "`\(\<[A-Z][a-zA-Z0-9_']*\.\)\=[A-Z][a-zA-Z0-9_']*`"
+syn match hsVarSym "` *\(\<[A-Z][a-zA-Z0-9_']*\.\)\=[a-z][a-zA-Z0-9_']* *`"
+syn match hsConSym "` *\(\<[A-Z][a-zA-Z0-9_']*\.\)\=[A-Z][a-zA-Z0-9_']* *`"
 
 " (Non-qualified) identifiers which start with # are labels
 syn match hsLabel "#[a-z][a-zA-Z0-9_']*\>"