prefix-minus-resolution.md

+# Proposal: [PrefixMinusResolution](prefix-minus-resolution)
+
+<table><tr><th> Ticket       </th>
+<th></th></tr>
+<tr><th> Dependencies </th>
+<th></th></tr>
+<tr><th> Related      </th>
+<th>[FixityResolution](fixity-resolution)[NegativeSyntax](negative-syntax)[NegationBindsTightly](negation-binds-tightly)</th></tr></table>
+
+## Compiler support
+
+<table><tr><th> GHC   </th>
+<th> \[ none \] 
+</th></tr>
+<tr><th> nhc98 </th>
+<th> \[ none \] 
+</th></tr>
+<tr><th> Hugs  </th>
+<th> \[ partial \] 
+</th></tr>
+<tr><th> UHC   </th>
+<th> \[ unknown \] 
+</th></tr>
+<tr><th> JHC   </th>
+<th> \[ none \] 
+</th></tr>
+<tr><th> LHC   </th>
+<th> \[ unknown \] 
+</th></tr></table>
+
+## Summary
+
+
+Resolve more prefix minus application unambiguously.
+
+
+As described in [NegationBindsTightly](negation-binds-tightly) ghc rejects same terms
+that are accepted by Hugs and Helium and should not be rejected in general.
+However, making negation bind more tightly is not the proposed solution here, because
+it would (in my eyes) wrongly resolve "`- x ^ 2`" to "`(-1) ^ 2`".
+
+1. Only operators to the right of prefix negation need to be considered for resolution.
+
+
+This condition ensures that "4 \* -5" is not rejected (as ghc does).
+
+1. Prefix minus should bind less tight than multiplication but (slightly) stronger than addition and subtraction.
+
+
+The latter condition ensures that "- x \# …" is resolved as "(- x) \# …" for any operator \# with lower precedence than multiplication.
+
+
+"-4 \* 5" will be resolved to "-(4 \* 5)" as Hugs correctly does already.
+I don't know how Helium resolves this, but it does (usually) not matter for multiplication if it were resolved to "(-4) \* 5".
+
+
+However, Hugs rejects "-4 \# 5" for a non-left-associative operator \# with precedence 6, because it compares associativities for operators with the same precedence. Therefore prefix minus should have a (slightly) higher precedence than infix operators with the precedence of infix minus.
+
+```wiki
+infix # 6
+(#) = undefined
+x7 = -4 # 5
+x8 = 4 # -5
+```
+
+
+x7 and x8 should be accepted, too. They are currently rejected by Hugs and ghc.
+
+
+As an option it is possible to support multiple prefix minus application. ("4 \* - - 5" can be resolved in the same way as
+"4 \* - 5" is).
+
+
+For other examples see
+[ http://www.haskell.org/pipermail/haskell-prime/2010-July/003229.html](http://www.haskell.org/pipermail/haskell-prime/2010-July/003229.html)
+
+## Description
+
+## References
+
+## Report Delta
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