HELP SCON                                    Robert Duncan, January 1990

Union of Standard ML special constant types.


    CONTENTS - (Use <ENTER> g to access required sections)

 -- The Scon Module
 -- The Scon Type


-- The Scon Module ----------------------------------------------------

signature Scon
structure Scon : Scon
    The structure  -Scon- is  an autoloadable  library module  with  the
    following signature:

        signature Scon = sig

            datatype scon
                INT of int
            |   REAL of real
            |   STRING of string

        end


-- The Scon Type ------------------------------------------------------

datatype scon
con INT (i : int)
con REAL (r : real)
con STRING (s : string)
    The type -scon- is the union  of the three SML ``special  constant''
    types: integer,  real and  string. These  types are  defined in  the
    pervasive structure  -StdTypes-  (see  HELP *  STDTYPES).  They  are
    special in that their values are denoted by lexical constants rather
    than by datatype constructors or  by predefined variables, and  they
    are basic to the construction  of user-defined structured types.  In
    many circumstances the handling of  the three types is similar,  and
    the -scon- type is provided as a convenience to allow such  handling
    to be packaged into a single  function. It also allows some  general
    purpose functions to  be written which  work on the  union type  for
    which there would otherwise be required three separate versions.


--- C.all/pml/help/scon
--- Copyright University of Sussex 1991. All rights reserved. ----------