Paul Johnson wrote:
I'm using arrows for the first time, with HXT. I think I'm getting the
hang of it, but one problem has me stumped. I have a function
"lookupFormatter" which takes a string and returns an arrow, and I want
to use that arrow. Something like this:
myProblem :: (ArrowXml a) -> a XmlTree String
myProblem = proc xml do
name <- getAttrValue "name" -< xml
fmt <- arr lookupFormatter -< name
fmt -< xml
But I can't figure out how to do it. I get "fmt: not in scope".
ArrowApply is one way, if there is an instance for it:
module Main where
import Control.Arrow
adder :: (Arrow a) => Int -> a Int Int
adder i = arr (i+)
adderUser :: (ArrowApply a, Arrow a) => a Int Int
adderUser = proc x -> do
a <- arr adder -< x
y <- app -< (a,x)
returnA -< y
main = mapM_ (print . (adderUser :: (->) Int Int)) [1..10]
Claude
--
http://claudiusmaximus.goto10.org
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