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module str_arit
/*
String Arithmetic.
This program demonstrates string arithmetic by mergesorting the characters of a large string.
*/
import StdEnv
// *S is needed to create the large string.
mul_S::Int String -> String
mul_S 0 string = ""
mul_S n string = string +++ mul_S (n-1) string
// The mergesort algorithm on strings.
MergeSort::String -> String
MergeSort str
| len<=1 = str
| otherwise = Merge (MergeSort first) (MergeSort second)
where
first = str%(0,middle - 1)
second = str%(middle,len - 1)
middle = len /2
len = size str
Merge::String String -> String
Merge str "" = str
Merge "" str = str
Merge str1 str2
| ch1<ch2 = ch1 +++ Merge (RemoveFirstChar str1) str2
| otherwise = ch2 +++ Merge str1 (RemoveFirstChar str2)
where
ch1 = str1%(0,0)
ch2 = str2%(0,0)
RemoveFirstChar::String -> String
RemoveFirstChar string = string%(1,size string-1)
// The Start rule: sort a large string (30*40 characters).
Start::String
Start = MergeSort (mul_S 30 "Sort this garbage properly, please :-). ")
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