Bulat Ziganshin wrote:
Hello Brian,
Saturday, August 19, 2006, 12:21:34 PM, you wrote:
ie putting a '.' before each field name. The intended meaning is that dotted field names do *not* generate top level functions. Instead they allow the compiler to generate instance decls as follows, where we've introduced a new form of identifier, the dotted id, which behaves as a postfix operator which binds more tightly than function application and can also be used as a class name (by the compiler only):
class (.x) :: a b | a -> b where (.x) :: a -> b
this means that foo.bar should be parsed differently by _lexer_ depending on is there any .bar field available in current or any imported module
Hi Bulat, I just assumed that foo.bar would always be lexed as "foo" ".bar" so if composition was intended there would need to be a space between the "." and the "bar", but this breaks backwards compatibility (I hadn't thought of this when I made the proposal because I assumed everyone always writes "f . g" and not "f.g" when they mean composition but of course the latter is currently parsed as composition also).
How about omitting '.' and using '#' operation for record access? the only problem will that '#' should have larger priority than ' '. i.e. function application. I had proposal on it, but it's too daring - raise priority of operations when they are written without spaces around, i.e.
object#call x+y t#field z*2+1
treated as
(object#call) (x+y) (t#field) (z*2+1)
Intuitively this makes sense, because you'd expect no spaces to mean "glue this together as tight as possible", but on the other hand I personally find the second version with brackets is visually much easier to read even though it's a bit more inconvenient to write. But 1) The first version is not backwards compatible either. 2) object#call should not be treated as (object # call) because it means ((#call) object) so whatever symbol is used for field selection, it needs to be glued onto the field name by the lexer not the parser. Also I was hoping to be able to use the "." so that field access would follow the C, C#, Java conventions and because # is used by ghc to mean "unboxed" so the following might be confusing: object#call 1# x#y # k (#g,a#) object.call 1# x.y # k (#g,a#) ie ((object.call) 1# (x.y)) # (k (# g, a #)) Best regards, Brian -- Logic empowers us and Love gives us purpose. Yet still phantoms restless for eras long past, congealed in the present in unthought forms, strive mightily unseen to destroy us. http://www.metamilk.com