Re: [Haskell-cafe] Re: Translating perl -> haskell, string "fill ins" with an error on invalid inputseems awfullycomplex. Is there a way to simplify?

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Transpose using array comprehension

Thomas Hartman

15 Apr 2007 15 Apr '07

7:03 a.m.

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.

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jeff p

15 Apr 15 Apr

11:20 p.m.

New subject: 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

Thomas Hartman

16 Apr 16 Apr

7:45 a.m.

New subject: 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 :

...

{----

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

Claus Reinke

9:18 a.m.

New subject: 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, ..

as i mentioned, it is not difficult to hack something up, and in many cases, efficiency doesn't matter much for this part of the problem (though a standard, efficient, well-designed library would be welcome). but if we compare the attached example with here docs in perl or shell or .., we find that we can get rid of all that escaping and concatenation in strings, but: - the file name should be implicit (the current source) - the dictionary should be implicit (the current variable environment) the former might be easy to add to the language, and the latter would be a minor subset of template haskell functionality. but they need to be standardized and widely available to be of much use. claus ps here's the output: $ runhaskell Here.hs this is a poor man's here-document with quotes ", and escapes \, and line-breaks, and layout without escaping \" \\ \n, without concatenation. oh, and with some variables, $(too). <html> <head><title>very important page</title></head> <body> <verb> this is a poor man's here-document with quotes ", and escapes \, and line-breaks, and layout without escaping \" \\ \n, without concatenation. oh, and with some variables, $(too). </verb> </body> </html>

Thomas Hartman

9:58 a.m.

New subject: Translating perl -> haskell, string "fill ins" with an error on invalid inputseems awfullycomplex.Is there a way to simplify?

I put this on the haskell wiki at http://haskell.org/haskellwiki/Poor_Man%27s_Heredoc_in_Haskell So far I have only linked this from http://haskell.org/haskellwiki/Simple_unix_tools I feel like the wiki deserves a section on "Haskell Template Solutions" distinct from this. However, there is a bit of a namespace conflict, as "template haskell" is a ghc extension, and so if you google on it you will get all stuff first. I wonder if anyone has an opinion on a good title for a wiki page about this. Haskell String Interpolation? Haskell String Templates? But these sound clunky to me. 2007/4/16, Claus Reinke :

...

...
With regards to the variable interpolation in strings problem, ..

as i mentioned, it is not difficult to hack something up, and in many cases, efficiency doesn't matter much for this part of the problem (though a standard, efficient, well-designed library would be welcome). but if we compare the attached example with here docs in perl or shell or .., we find that we can get rid of all that escaping and concatenation in strings, but:

- the file name should be implicit (the current source) - the dictionary should be implicit (the current variable environment)

the former might be easy to add to the language, and the latter would be a minor subset of template haskell functionality. but they need to be standardized and widely available to be of much use.

claus

ps here's the output:

$ runhaskell Here.hs

this is a poor man's here-document

with quotes ", and escapes \, and line-breaks, and layout without escaping \" \\ \n, without concatenation.

oh, and with some variables, $(too).

<html> <head><title>very important page</title></head> <body> <verb>

this is a poor man's here-document

with quotes ", and escapes \, and line-breaks, and layout without escaping \" \\ \n, without concatenation.

oh, and with some variables, $(too).

</verb> </body> </html>

Thomas Hartman

18 Apr 18 Apr

8:33 a.m.

New subject: 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 :

...

{----

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

Thomas Hartman

8:36 a.m.

New subject: Translating perl -> haskell, string "fill ins" with an error on invalid inputseems awfullycomplex. Is there a way to simplify?

Without the flag: thartman@linodehaskell:~/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' thartman@linodehaskell:~/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 65 yv <- mystr y 66 return $ xv ++ yv 67 2007/4/18, Thomas Hartman :

...

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 :

...
{----

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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Claus Reinke
jeff p
Thomas Hartman