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module Miscellaneous(
if',
(?),
selectFrom
) where
import qualified Control.Monad as Con
import qualified Data.List as List
import qualified Data.Maybe as Maybe
if' :: Bool -> t -> t -> t
if' a b c = if a then b else c
infixr 1 ?
(?) :: Bool -> t -> t -> t
(?) = if'
-- kinda functions like poor man's sql
-- first argument is the indices of the items you want in the results
-- second argument is index-item pairs to dictate what records are acceptable to select from
-- third argument is the list of items that makes up the record under consideration
-- then if the record was deemed acceptable you get the bits you wanted
-- (note that all indices start from 1)
selectFrom :: (Num t, Eq t, Eq a, Enum t) => [t] -> [(t,a)] -> [a] -> Maybe [a]
selectFrom pick has from =
let foldFunc r i =
let check = List.lookup (fst i) has
in if (Maybe.isNothing check || Maybe.fromJust check == snd i)
then if (List.elem (fst i) pick)
then Just (r ++ [snd i])
else Just r
else Nothing
in Con.foldM foldFunc [] (zip [1,2..] from)
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