Malcolm Wallace schrieb:
I'm asking for support of: http://hackage.haskell.org/trac/haskell-prime/wiki/PrefixMinusResolution
Just to note that nhc98 appears to fulfill the outcome of this resolution algorithm already, with the exception of example x7, which is parsed as -(4#5).
Because it seems to (unnecessarily) check if the operator # is left-associative. I assume that for "infixr 6 #" the term "-4 # 5 # 6" is resolved as "-(4 # (5 # 6))" (like it would be for "^"). How can I try out nhc98? My old installation is broken and http://www.haskell.org/haskellwiki/Implementations#nhc98 refers to no implementation. Is Yhc the compiler I should try?
However, nhc98 goes further and permits the declaration of arbitrary prefix operators, using the syntax
prefix negate 6 -
yes, this is a nice extension.
yes, in addition to
infix 6 -
I think the rationale is that the prefix symbol must map to a non-symbolic function name, because the same symbol may also refer to a function of a different type when used infix.
Currently there is no haskell way to _define_ a prefix operator therefore prefix minus is bound to negate explicitly as above (nhc98) or implicitly built-in (ghc and hugs). Prefix- and Infix-usage can be distinguished by the lexer: - a ... -> prefix a - ... -> infix Furthermore, prefix minus can not be qualified (bug or feature?). Prelude.- only refers to the infix version and "Prelude.- 1" is rejected (by ghc and hugs). Cheers Christian