Answering my own plea for help, I now have the following, which seems
neater to me.
checking Maybes is best done in the Maybe Monad, or if you need specific error
messages, using maybe. that, in turn can be abstracted out into a lookup with error
message. once the checking is done in the wrapper, there is no need to repeat
it in
the generator. also, the interface to the generator is too wide for the small
amount of
extra functionality it provides, so it is probably best inlined, and there
seems to be no
need to commit to IO so early. i also tend to use [String], with a final
unlines before
output, but that is a matter of opinion, i guess.
financial_output :: String -> String -> String -> 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 (error $ "no company file for " ++ company)
company company_to_companyfile
modeString = lookupWith (error $ "no mode string for " ++ displaymode)
displaymode displaymode_to_modestring
titleEnd = lookupWith (error $ "no title end for " ++ displaymode)
displaymode displaymode_to_titleend
lookupWith error key assocs = maybe error id $ lookup key assocs
hth,
claus
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