Explicit Implicit Parameters
Stc
Date: 2005-06-02
Time: 11:45
Room: CGN room C004
Title: Explicit implicit parameters
Abstract
In almost all languages arguments to functions are to be given
explicitly. The Haskell class system however is
an exception: functions can have class predicates as part of their
type signature, and dictionaries are implicitly
constructed and implicitly passed as hidden arguments, thus relieving
the programmer from a lot of clerical work
and removing clutter from the program text. Unfortunately Haskell
maintains a very strict boundary between
the implicit and the explicit world; if the implicit mechanisms fail
to construct the hidden dictionaries there is no
way the programmer can provide help, nor is he able to override the
choices made by the implicit mechanisms.
In this paper we describe, in the context of Haskell, a mechanism
that allows the programmer to explicitly pass
implicit parameters. This extension blends well with existing
resolution mechanisms, since it only overrides
the default behavior of such mechanisms. We also describe its
implementation. We include a description of the
use of partial type signatures, liberating the programmer from having
to choose between specifying a complete
type signature or no type signature at all. Finally we show how the
system can easily be extended to deal with
higher-order predicates, thus enabling the elegant formulation of
some form of generic programming.
See also
Ehc,
Atze
