negation-binds-tightly.md

+# Proposal: NegationBindsTightly
+
+<table><tr><th> Ticket       </th>
+<th>\#999</th></tr>
+<tr><th> Dependencies </th>
+<th> names of other proposals on which this one depends 
+</th></tr>
+<tr><th> Related      </th>
+<th>[NegativeSyntax](negative-syntax)</th></tr></table>
+
+## Compiler support
+
+
+None at present
+
+## Summary
+
+
+Which of these definitions are correct Haskell?
+
+```wiki
+  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
+
+```wiki
+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
+
+```wiki
+    lexp6    ->      - exp7
+```
+
+
+and adding the production
+
+```wiki
+    exp10    ->      - fexp
+```
+
+
+but this relates to Haskell 98 rather than Haskell 2010, so the exact change will differ.