Please only use SML / ML code. Do not copy the codes on chegg, they're wrong. Write a function int2str to convert an integer to a string int2str(1234) → "1234", int2str(~1234) → "~1234" Write a...

Please only use SML / ML code. Do not copy the codes on chegg, they're wrong.

1. Write a functionint2str to convert an integer to a string
   
   int2str(1234) → "1234", int2str(~1234) → "~1234"
   


2. Write a functionstr2int to convert a string to an integer (assume that the number is always valid)
   
   str2int("1234") → 1234, str2int("~1234") → ~1234
   


3. Write a functionpairStarto form a new string where identical chars that
   are adjacent in the original string are separated from each other by a "*"
   
   pairStar("xxyy") → "x*xy*y", pairStar("aaaa") → "a*a*a*a"