What is the size of int?

ML has a type of integers. Fine; but how large is the underlying representatinon? 16 bit? 32 bit? 64 bit?

So I read this page about SML and based—indirectly—on that reading, here’s how I found out …

• … in SML:

  
  

  $ rlwrap sml
  Standard ML of New Jersey v110.69 [built: Mon Jun  8 14:15:08 2009]
  - Int.precision;
  [autoloading]
  [library $SMLNJ-BASIS/basis.cm is stable]
  [autoloading done]
  val it = SOME 31 : int option
  - Int.minInt;
  val it = SOME ~1073741824 : int option
  - Int.maxInt;
  val it = SOME 1073741823 : int option

• … and in PolyML:

  
  

  $ rlwrap poly
  Poly/ML 5.2 Release
  > Int.precision;
  val it = NONE : Int.int option
  > Int.minInt;
  val it = NONE : Int.int option
  > Int.maxInt;
  val it = NONE : Int.int option

Some comments:

• SML autoloads the package providing Int.precision as needed. Don’t worry about it.
• The option type-former in int option indicates that the function might return NONE or a value SOME x where x:int.
• PolyML has infinite-precision arithmetic as default, so Int.minInt returns NONE because there is no least integer.
• SML has 31 bit integers by default—which gives you between plus and minus one billion. Thus Int.minInt returns SOME ~1073741824.
  (The extra bit is reserved by the implementation to indicate whether a word is an integer or a pointer.)

PolyML is another ML implementation, and a rather nice one. If you are fortunate enough to be using a Debian-based Linux, you can get it by typing in

sudo apt-get install polyml

You can also type in

sudo apt-get install xaos