Re: [Haskell-cafe] Re: Translating perl -> haskell, string "fill ins" with an error on invalid inputseems awfullycomplex. Is there a way to simplify?
Without the flag:
[EMAIL
PROTECTED]:~/websites/gnuplotwebinterface/cgi-bin/gnuplot-scripts>./financial2.hs
cisco candles 31-May-04 11-Jun-04
./financial2.hs:58:0:
Illegal instance declaration for `MyString (Either String String)'
(The instance type must be of form (T a b c)
where T is not a synonym, and a,b,c are distinct type variables)
In the instance declaration for `MyString (Either String String)'
./financial2.hs:61:0:
Illegal instance declaration for `MyString String'
(The instance type must be of form (T a b c)
where T is not a synonym, and a,b,c are distinct type variables)
In the instance declaration for `MyString String'
[EMAIL PROTECTED]:~/websites/gnuplotwebinterface/cgi-bin/gnuplot-scripts>cat
--number financial2.hs | tail
58 instance MyString (Either String String)
59 where mystr = id
60
61 instance MyString String
62 where mystr = Right
63
64 x <++> y = do xv <- mystr x
65yv <- mystr y
66return $ xv ++ yv
67
2007/4/18, Thomas Hartman <[EMAIL PROTECTED]>:
Looks like this needs to be run with
#!/usr/lib/ghc-6.6/bin/runghc
{-# OPTIONS_GHC -fglasgow-exts #-}
to get
instance MyString (Either String String)
where mystr = id
instance MyString String
where mystr = Right
to work.
I'm curious if there is a community feeling on whether glasgow-exts is
sort of a de-facto standard now? Or is it common to try to get things
to work without this, for maximum portability?
Is there an easy way to get the above to work without the compiler flag?
2007/4/16, jeff p <[EMAIL PROTECTED]>:
> {
>
> Hello,
>
> Here is a variation on Claus' code which returns an Either type
> rather than fails with error. This could be further generalized to use
> any instance of MonadError, rather than Either.
>
> -Jeff
>
> }
>
> import Control.Monad.Error
>
> financial_output :: String -> String -> String -> String -> Either String
String
> financial_output company displaymode startDate endDate = financial_script
> where
> financial_script = gnuplot_timeseries_settings <++> "\n"
> <++> "plot [\"" <++> startDate <++> "\":\""
> <++> endDate <++> "\"]"
> <++> " '" <++> companyFile <++> "'" <++> modeString
> <++> " title \"" <++> company <++> " " <++>
> titleEnd <++> "\""
>
> companyFile = lookupWith ("no company file for " ++ company)
> company company_to_companyfile
>
> modeString = lookupWith ("no mode string for " ++ displaymode)
> displaymode displaymode_to_modestring
>
> titleEnd= lookupWith ("no title end for " ++ displaymode)
> displaymode displaymode_to_titleend
>
> lookupWith :: (Eq a) => String -> a -> [(a,String)] -> Either String String
> lookupWith error key assocs = maybe (Left error) Right $ lookup key assocs
>
> class MyString a
> where mystr :: a -> Either String String
> instance MyString (Either String String)
> where mystr = id
> instance MyString String
> where mystr = Right
>
> x <++> y = do xv <- mystr x
> yv <- mystr y
> return $ xv ++ yv
>
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Re: [Haskell-cafe] Re: Translating perl -> haskell, string "fill ins" with an error on invalid inputseems awfullycomplex. Is there a way to simplify?
Looks like this needs to be run with
#!/usr/lib/ghc-6.6/bin/runghc
{-# OPTIONS_GHC -fglasgow-exts #-}
to get
instance MyString (Either String String)
where mystr = id
instance MyString String
where mystr = Right
to work.
I'm curious if there is a community feeling on whether glasgow-exts is
sort of a de-facto standard now? Or is it common to try to get things
to work without this, for maximum portability?
Is there an easy way to get the above to work without the compiler flag?
2007/4/16, jeff p <[EMAIL PROTECTED]>:
{
Hello,
Here is a variation on Claus' code which returns an Either type
rather than fails with error. This could be further generalized to use
any instance of MonadError, rather than Either.
-Jeff
}
import Control.Monad.Error
financial_output :: String -> String -> String -> String -> Either String String
financial_output company displaymode startDate endDate = financial_script
where
financial_script = gnuplot_timeseries_settings <++> "\n"
<++> "plot [\"" <++> startDate <++> "\":\""
<++> endDate <++> "\"]"
<++> " '" <++> companyFile <++> "'" <++> modeString
<++> " title \"" <++> company <++> " " <++>
titleEnd <++> "\""
companyFile = lookupWith ("no company file for " ++ company)
company company_to_companyfile
modeString = lookupWith ("no mode string for " ++ displaymode)
displaymode displaymode_to_modestring
titleEnd= lookupWith ("no title end for " ++ displaymode)
displaymode displaymode_to_titleend
lookupWith :: (Eq a) => String -> a -> [(a,String)] -> Either String String
lookupWith error key assocs = maybe (Left error) Right $ lookup key assocs
class MyString a
where mystr :: a -> Either String String
instance MyString (Either String String)
where mystr = id
instance MyString String
where mystr = Right
x <++> y = do xv <- mystr x
yv <- mystr y
return $ xv ++ yv
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Re: [Haskell-cafe] Re: Translating perl -> haskell, string "fill ins" with an error on invalid inputseems awfullycomplex. Is there a way to simplify?
With regards to the variable interpolation in strings problem, it's
probably worth watching
http://groups.google.de/group/fa.haskell/browse_thread/thread/34741c2a5c311a17/286dbd62748ef1c1?lnk=st&q=%22haskell+cafe%22+%22template+system%22&rnum=1&hl=en#286dbd62748ef1c1
which mentions some perl/python-like template systems in the works for haskell.
2007/4/16, jeff p <[EMAIL PROTECTED]>:
{
Hello,
Here is a variation on Claus' code which returns an Either type
rather than fails with error. This could be further generalized to use
any instance of MonadError, rather than Either.
-Jeff
}
import Control.Monad.Error
financial_output :: String -> String -> String -> String -> Either String String
financial_output company displaymode startDate endDate = financial_script
where
financial_script = gnuplot_timeseries_settings <++> "\n"
<++> "plot [\"" <++> startDate <++> "\":\""
<++> endDate <++> "\"]"
<++> " '" <++> companyFile <++> "'" <++> modeString
<++> " title \"" <++> company <++> " " <++>
titleEnd <++> "\""
companyFile = lookupWith ("no company file for " ++ company)
company company_to_companyfile
modeString = lookupWith ("no mode string for " ++ displaymode)
displaymode displaymode_to_modestring
titleEnd= lookupWith ("no title end for " ++ displaymode)
displaymode displaymode_to_titleend
lookupWith :: (Eq a) => String -> a -> [(a,String)] -> Either String String
lookupWith error key assocs = maybe (Left error) Right $ lookup key assocs
class MyString a
where mystr :: a -> Either String String
instance MyString (Either String String)
where mystr = id
instance MyString String
where mystr = Right
x <++> y = do xv <- mystr x
yv <- mystr y
return $ xv ++ yv
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Re: [Haskell-cafe] Re: Translating perl -> haskell, string "fill ins" with an error on invalid inputseems awfullycomplex. Is there a way to simplify?
{
Hello,
Here is a variation on Claus' code which returns an Either type
rather than fails with error. This could be further generalized to use
any instance of MonadError, rather than Either.
-Jeff
}
import Control.Monad.Error
financial_output :: String -> String -> String -> String -> Either String String
financial_output company displaymode startDate endDate = financial_script
where
financial_script = gnuplot_timeseries_settings <++> "\n"
<++> "plot [\"" <++> startDate <++> "\":\""
<++> endDate <++> "\"]"
<++> " '" <++> companyFile <++> "'" <++> modeString
<++> " title \"" <++> company <++> " " <++>
titleEnd <++> "\""
companyFile = lookupWith ("no company file for " ++ company)
company company_to_companyfile
modeString = lookupWith ("no mode string for " ++ displaymode)
displaymode displaymode_to_modestring
titleEnd= lookupWith ("no title end for " ++ displaymode)
displaymode displaymode_to_titleend
lookupWith :: (Eq a) => String -> a -> [(a,String)] -> Either String String
lookupWith error key assocs = maybe (Left error) Right $ lookup key assocs
class MyString a
where mystr :: a -> Either String String
instance MyString (Either String String)
where mystr = id
instance MyString String
where mystr = Right
x <++> y = do xv <- mystr x
yv <- mystr y
return $ xv ++ yv
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Re: [Haskell-cafe] Re: Translating perl -> haskell, string "fill ins" with an error on invalid inputseems awfullycomplex. Is there a way to simplify?
Claus and Evan ++; that was very helpful. FWIW, my gut feeling is that Claus's first version was easier to understand than the revision with printf, which seems to me to involve a lot more monadic wizardry (Functor, MonadError, fmap, mapm). The first version, which just used maybe, was clear to me within seconds. But again, I learned a lot. Thanks. ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Translating perl -> haskell, string "fill ins" with an error on invalid inputseems awfullycomplex. Is there a way to simplify?
by utilizing Text.Printf.printf, extracting some more common functionality for the lookups,
and changing the error handling (check for errors before giving results, but use throwError
instead of error, letting the caller decide whether errors are fatal or not), we arrive at
something like:
financial_output :: (Functor m, MonadError String m)
=> String -> String -> String -> String -> m String
financial_output company displaymode startDate endDate =
fmap financial_script $ mapM lookupWith lookups
where
financial_script [companyFile,modeString,titleEnd] =
gnuplot_timeseries_settings ++ "\n"
++ printf "plot [\"%s\":\"%s\"] '%s'%s title \"%s %s\""
startDate endDate companyFile modeString company titleEnd
lookups = [ ("no company file for ", company, company_to_companyfile)
, ("no mode string for ", displaymode, displaymode_to_modestring)
, ("no title end for ", displaymode, displaymode_to_titleend)
]
lookupWith (msg,key,assocs) = maybe (throwError $ msg ++ key) return $ lookup key assocs
which perhaps isn't all that bad? the main thing i miss in Haskell for this
kind of code
generators are here-documents. there are workarounds (Hugs has a form of here
docs,
string interpolation isn't difficult to hack up, unlines gets rid of ++ and
"\n"), and for
more complex code generators, use of Text.PrettyPrint may be more appropriate, but
for everyday scripting with code generation, nothing is as simple, readable, or portable
as good old here-documents.
hth,
claus
ps. calling the modified function:
Main> either error putStrLn $ financial_output "ibm" "point" "start" "end"
Program error: no mode string for point
Main> either error putStrLn $ financial_output "ibm" "points" "start" "end"
set terminal png transparent nocrop enhanced size 600,400
set pm3d implicit at s
set xdata time # The x axis data is time
set timefmt "%d-%b-%y" # The dates in the file look like 10-Jun-04
set format x "%b %d" #On the x-axis, we want tics like Jun 10
plot ["start":"end"] 'data/ibm.dat'using 1:2 with linespoints title "ibm daily
prices"
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