new keyword: infixlr?
S. Doaitse Swierstra
doaitse at cs.uu.nl
Fri Sep 10 13:51:10 EDT 2010
Currently Haskell has infix, infixl and infixr operators. I see a use for infixlr as well. This indicates that the implemtation may assume the operator to be associative, and thus has the freedom to "balance" an expression containing several operator occurrences.
The reason that I bring up this is that in a new combinator I have added to my parser library (the <||> in Text.ParserCombinators.UU.Derived) internally uses cartesian products, which are being constructed and updated. If the compiler had the right to interpret the expressions a <||> b <||>c <||> d as e.g. (a <||> b) <||> (c <||> d) then the updating time for would go down from O(n) to O(log n).
I admit it is probably a minor point, but given the increased use of "type level" programming, and the use of cartesian products to keep "lists of values of a different type", I can also see many good uses for this.
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