AAFPA/Ch5 - 大久保弘崇

p.89 L.-15, -3 Errata

Add ')' before '=>'

p.90 show for List based Stack

Re-construction of Stk xs from Stk (x:xs) made me sorrow.

showsPrec _ (Stk []) = showChar '-'
showsPrec _ (Stk s)  = foldr (\x y->shows x.showChar '|'.y) (showChar '-') s
 

p.94 def of inSet

Single comparison to x

inSet x (St s) = (not.null.takeWhile (== x).dropWhile (< x)) s