Okay, first steps:
1. A Trac ticket (#1318,
http://hackage.haskell.org/trac/ghc/ticket/1318) (is "feature request" a
good category, versus "task"?)
2. A test-case to make sure I don't break anything with existing '-'
syntax. I'm guessing it should go in
testsuite/tests/ghc-regress/parser/should_run/, although maybe since it
checks Haskell-98 compatibility it should go in the testsuite/tests/h98
directory? (tested ghc and hugs, which both pass)
Isaac
(test-case attached in case anyone wants to look at or review it; I'll
send a darcs patch adding the testcase once I know where to put it)
-- !!! Haskell-98 prefix negate operator
-- Make sure the parsing is actually the correct
-- one by running this after it's compiled.
negatedExpression = - (3 + 4)
negatedTightlyBinding = -3^4
negatedNonSection = (- 3)
negatedNonSectionWithHighPrecedenceOp =
let { f = (+); infix 9 `f` } in ( -3 `f` 4 )
negatedNonSectionWithLowPrecedenceOp =
let { f = (+); infix 1 `f` } in ( -3 `f` 4 )
negatedRightHandSide =
-- This is actually not legal syntax: 3 * - 4
-- However, lower-precedence binary ops work.
-- (see H98 syntax for exp, or imagine it's because it
-- would parse differently as 3 * 0 - 4)
let { f = (+); infix 1 `f` } in ( 3 `f` - 4 )
subtractionNotNegation = 3 -4
negativePattern =
case -3 of { (- 3) ->
case -4 of { - 4 ->
True } }
-- not legal H98 syntax: case -4 of { _x @ -4 ->
-- (parentheses needed) case -5 of { ~ -5 ->
subtractionNotNegationPattern =
-- defines infix '-' (shadowing Prelude definition)
let { 3 -4 = True } in (3 - 4)
precedenceOfNegationCantBeChanged =
let { (-) = undefined; infix 9 - } in (- 3 * 4)
negationCantBeQualified =
(Prelude.-3) 4
main = do
print negatedExpression
print negatedTightlyBinding
print negatedNonSection
print negatedNonSectionWithHighPrecedenceOp
print negatedNonSectionWithLowPrecedenceOp
print negatedRightHandSide
print subtractionNotNegation
print negativePattern
print subtractionNotNegationPattern
print precedenceOfNegationCantBeChanged
print negationCantBeQualified
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