= Proposal: !NegationBindsTightly =

|| Ticket       || #135 ||
|| Dependencies || names of other proposals on which this one depends ||
|| Related      || [wiki:NegativeSyntax] ||

== Compiler support ==

None at present

== Summary ==

Which of these definitions are correct Haskell?
{{{
  x1 = 4 + -5
  x2 = -4 + 5
  x3 = 4 - -5
  x4 = -4 - 5
  x5 = 4 * -5
  x6 = -4 * 5
}}}
Ghc accepts x2, x4, x6 and rejects the others with a message like
{{{
Foo.hs:4:7:
    Precedence parsing error
        cannot mix `+' [infixl 6] and prefix `-' [infixl 6] in the same infix expression
}}}
Hugs and Helium accept them all.  I think that Hugs is right here.  After all, there is no ambiguity in any of these expressions.  And an application-domain user found this behaviour very surprising.

== Description ==

Make unary minus bind more tightly than any other operator.  But not more tightly than function application.

== References ==

External references, papers, articles, support in other languages.

== Report Delta ==

Something like deleting
{{{
    lexp6    ->      - exp7
}}}
and adding the production
{{{
    exp10    ->      - fexp
}}}
but this relates to Haskell 98 rather than Haskell 2010, so the exact change will differ.