SIGNATURE BTUnion

-- provides Union-Datetype of basic types and strings

IMPORT Nat ONLY nat
       Int ONLY int
       Real ONLY real
       Char ONLY char
       String ONLY string
       Seq[union] ONLY seq

TYPE union      == nat(nat:nat)         -- union of basic types
                   int(int:int)         -- and strings
                   real(real:real)
                   char(char:char)
                   string(string:string)
                   bool(bool:bool)
                   denotation(denotation:denotation)
                   
                   

-- for easy writing of union-sequences
FUN u : nat        ** seq[union] -> seq[union]   -- n u seq == nat(n) :: seq
    u : int        ** seq[union] -> seq[union]   -- similar for the other
    u : real       ** seq[union] -> seq[union]   -- types
    u : char       ** seq[union] -> seq[union]
    u : string     ** seq[union] -> seq[union]
    u : bool       ** seq[union] -> seq[union]
    u : denotation ** seq[union] -> seq[union]

FUN u : nat        -> seq[union]      -- n u == nat(n) :: <>
    u : int        -> seq[union]      -- similar for the other types
    u : real       -> seq[union]
    u : char       -> seq[union]
    u : string     -> seq[union]
    u : bool       -> seq[union]
    u : denotation -> seq[union]