Removal candidates in patterns
O.Chitil at kent.ac.uk
Fri Jan 27 06:59:18 EST 2006
The arguments of Ian Lynagh, Ganesh Sittampalam, Claus Reinke and Cale
about restricting k patterns to class Integral, introducing a class
Natural and the role of class Eq prove my point that k patterns are
special, different from data constructors or character literals.
They are special, far more complex than most people think, and very easy
I do understand that probably everybody learning functional programming
learned k patterns very early on (in other languages such as Miranda
there is no overloading problem) and hence find it hard to make the
small change of using explicit equality instead. (And yes, removing
k-patterns will break a lot of Haskell programs.)
Higher-order functions substantially increase the expressivity of the
programming language. k-patterns are just an odd decorative element.
I was probably wrong to start my argument with talking about Hat. This
is just what made me personally look into k, n+k and ~ patterns. The
general argument is just that every language feature has its costs (for
tools, for research, for teaching,...) and hence any language feature
should be truely useful, not just convenient (naturally the distinction
is not clear cut).
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