<![CDATA[(* ---------------------------------------------------- *
* Handout for foundation routines for *
* D.Sem. labs; *
* This is the code for the fundamental *
* models of stores and environments. You will *
* need to provide the definitions of the types *
* used here, i.e. Denotable, Value, etc.. *
* ---------------------------------------------------- *)
(* -------------------------------------------- *)
(* ---------- Auxiliary Semantic Functions ---- *)
fun sum (x, y) = x + y:int;
fun diff (x, y) = x - y:int;
fun prod (x, y) = x * y:int;
fun lessthan (x, y) = x < (y:int);
(* ---------- Storage ---------- *)
(*
fun deallocate sto loc:Location = sto; (* ... later *)
*)
datatype Sval = stored of Storable | undef | unused;
(* --bot--- --top--- ----data--------- *)
datatype Store = store of Location * Location * (Location -> Sval);
val sto_init = fn loc:Location => unused;
val sto_null = store( 1, 0, sto_init);
fun update (store(bot,top,data), loc, v) =
let fun new adr = if adr=loc
then stored v else (data adr);
in store( bot, top, new)
end;
(* fetch from store, and convert into Storable (=Value) *)
fun fetch (store(bot,top,data), loc:Location) =
let fun stored_value(stored stble) = stble
| stored_value(unused) = raise fail
| stored_value(undef) = raise fail
in stored_value( data loc)
end;
(* create a new "undefined" location in a store *)
fun allocate ( store(bot,top,data) ) =
let val newtop = top+1
fun new adr = if adr=newtop
then undef else (data adr);
in (store( bot, newtop, new), newtop)
end;
(* ---------- Envirionment ---------- *)
type Environ = Ident -> Denotable;
val env_null = fn i:Ident => unbound;
fun bind (name, vl) = fn idn => if idn=(name:Ident)
then bound(vl) else unbound;
fun find (env:Environ, idn) =
let fun getbv(bound bdbl) = bdbl
| getbv(unbound) = raise fail
in getbv( env idn)
end;
fun overlay (env', env:Environ) =
fn idn => let val val' = env' idn
in if val'<>unbound then val'
else env idn
end;
]]>