-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Since the unary negation operator `-' is often considered a wart in Haskell's syntax and in many cases saying "negate" is arguably clearer anyway, I propose adding options to GHC to warn about its use. The only case I don't normally want to be warned about is "negative numeric literals", e.g. (-1), even if in current Haskell they do mean (negate (fromInteger 1)) not (fromInteger (negate 1)) (or equivalently, (fromInteger (negate (fromInteger 1))) as the inner fromInteger === id). I know this would be useful to someone since I caught myself manually cleaning some of my code in this way without the help of warning messages :) Proposed flag names and descriptions (could use a little tidying up) : - -fwarn-unary-minus Causes a warning to be emitted for all usages of the unary operator `-', except those in which its argument is a numeric literal that is not separated from the minus sign by any space (space includes comments). - -fwarn-all-unary-minus For those who hate it with a passion, this option warns about ALL uses of the unary `-' operator, even code like `(-1)'. Opinions? (Should I put a feature request in Trac? Is that what I perhaps should have done in the first place?) Is this simple enough to try to implement myself so I can start getting to know GHC's internals? (I suspect that detecting the adjacency of the "-" to a numeric literal without changing the actual precedence may be a little tricky... -2^6 parses as negate(2^6) and should get a warning, as should (- 2), IMO) Oh, the actual warning message... file:line:column: Warning: Unary minus in expression foo (or, on the next line, In the expression: foo ?) for an appropriate "foo", which has parentheses added to describe the effects of operator precedence, as usual for GHC diagnostic messages (it's just particularly important for making this one easy to understand in some cases) Isaac -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFGGBpSHgcxvIWYTTURAt5sAKCEIohHMiuUy9AofhWKzvDOf4rwmgCeJcbj e2RmW+UX2E6omuLpFfIH9fs= =1SnR -----END PGP SIGNATURE-----