Added simple examples

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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 :-). ")