On 11.05.2009, at 03:00, Rich Hickey wrote:
> Could you explain a bit why you needed to do this? I'm a bit concerned
> about libraries requiring symbol-macros.
Here is a simplified view of how my monad library works. Each monad
is an object that contains the definition of a few functions. Other
monadic functions are defined in terms of these basic functions.
Monads are applied by surrounding the code depending on the monadic
functions by (with-monad m ...) form, which is a macro that expands into
(let [m-result ... m-bind ... m-zero ... m-plus ...] ...)
The problem now is to define the monadic functions such that they
depend on the monad without having it as an explicit argument. My
initial solution was to first define a function that takes the four
basic functions as explicit arguments:
(defn --m-foo-- [m-result m-bind m-zero m-plus x y] (m-plus x y))
and then a macro that provides the desired interface:
(defmacro m-foo [x y] (--m-foo-- m-result m-bind m-zero m-plus x y))
This works fine for direct calls to m-foo, but since m-foo is not a
proper function, it cannot be passed as an argument to other
functions. The current implementation therefore uses symbol macros,
(defsymbolmacro m-foo (partial --m-foo-- m-result m-bind m-zero m-
plus))
removing all restrictions on the use of monadic functions. My recent
exchange with samppi concerns just a small detail: I had forgotten to
add symbol macros for the four basic monad functions.
Konrad.
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