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Motivation
module Motivation.Semigroup where
import Data.Monoid.All
import Data.String
instance semigroupFunction :: (Semigroup b) => Semigroup (a -> b) where
(<>) f g = \x -> f x <> g x
-- String examples.
noun = "strings"
verb = "form"
article = "a"
noun' = "`Semigroup`"
space = " "
subject = noun
predicate = verb <> space <> article <> space <> noun'
sentence :: String
sentence = subject <> space <> predicate
sentence' :: String
sentence' = noun
<> space
<> verb
<> space
<> article
<> space
<> noun'
bothCase :: String -> String
bothCase s = toUpper s <> toLower s
-- Parser examples.
startsWith :: String -> String -> All
startsWith s s' = All $ substr 0 (lengthS s') s == s'
endsWith :: String -> String -> All
endsWith s s' = All $ substr (lengthS s - lengthS s') (lengthS s') s == s'
lParen :: String -> All
lParen s = s `startsWith` "("
rParen :: String -> All
rParen s = s `endsWith` ")"
parens :: String -> All
parens = lParen <> rParen
startStop :: String -> String -> String -> All
startStop start stop = let startTest s = s `startsWith` start
stopTest s = s `endsWith` stop
in startTest <> stopTest
parens' :: String -> All
parens' = startStop "(" ")"
brackets :: String -> All
brackets = startStop "[" "]"
braces :: String -> All
braces = startStop "{" "}"
other :: String -> All
other = startStop "wat" "yup"
startMidStop :: String -> (String -> All) -> String -> String -> All
startMidStop start middleTest stop = let startTest s = s `startsWith` start
stopTest s = s `endsWith` stop
in startTest <> middleTest <> stopTest
contains :: String -> String -> All
contains s s' = All $ s `indexOfS` s' /= -1
thenElse :: String -> All
thenElse s = let afterThen = s `indexOfS` "then"
s' = substring afterThen (lengthS s) s
in s `contains` "then" <> s' `contains` "else"
rubyIfThenElse :: String -> All
rubyIfThenElse = startMidStop "if" thenElse "end"
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