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module Miscellaneous(
if',
(?),
(.:),
selectFrom,
readMaybe,
partBeforeAfter
) where
-- This source is licensed under Creative Commons CC0 v1.0.
-- To read the full text, see license.txt in the main directory of this repository
-- or go to https://creativecommons.org/publicdomain/zero/1.0/legalcode.txt
-- For a human readable summary, go to https://creativecommons.org/publicdomain/zero/1.0/
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'
-- with this, I have truly gone dotty
infixr 9 .:
(.:) :: (a -> b) -> (c -> d -> a) -> c -> d -> b
(.:) = (.).(.)
-- 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)
readMaybe :: Read a => String -> Maybe a
readMaybe s =
case reads s of
[(val, "")] -> Just val
_ -> Nothing
partBeforeAfter :: (Eq a) => a -> [a] -> ([a],[a])
partBeforeAfter item list =
let (x,y) = List.break (== item) list
in if (length y <= 1)
then (x,[])
else (x,tail y)
|
