datatype 'a Search = Found of 'a | NotFound ;
datatype Result = Ok | Error of string;
datatype Statement = Inspect of string | Update of string | Call of string;
datatype Method = Static | Dynamic;
 
type VarDecl = string*int;
type FunDecl = {name:string,
                vars:VarDecl list,
	                 body:Statement list};
			  
type MainDecl = {vars:VarDecl list,
                   funs:FunDecl list,
                    body:Statement list};

fun doesVarExist(varname:string,nil)= false
|   doesVarExist(varname,x::xs)=if #1(x:VarDecl)=varname then true 
				else doesVarExist(varname,xs); 

fun doesFexist(fname:string,nil)= false
|   doesFexist(fname,x::xs)=if #name(x:FunDecl)=fname then true
				else doesFexist(fname,xs);

fun mygetval(varname:string,x::xs)=if #1(x:VarDecl)=varname then #2(x)
				else mygetval(varname,xs);

fun getfun(fname:string,x::xs)=if #name(x:FunDecl)=fname then x
			else getfun(fname,xs);

fun tracestat (myprog:MainDecl, mymethod:Method, (Update k):Statement, myglobals:VarDecl list, myenv)=
	if doesVarExist(k,myenv@myglobals) 
	  then
	    (
	    print("Update "^k^":"^Int.toString(mygetval(k,myenv@myglobals))^"\n");
	    Ok
	    )
	  else
	    Error("Variable " ^ k ^ " could not be found")
|   tracestat (myprog, mymethod, (Inspect k), myglobals, myenv)=
	if doesVarExist(k,myenv@myglobals) 
	  then
	    (
	    print("Inspect "^k^":"^Int.toString(mygetval(k,myenv@myglobals))^"\n");
	    Ok
	    )
	  else
	    Error("Variable "^k^" could not be found")
|   tracestat (myprog, mymethod, (Call k), myglobals, myenv)=
	if doesFexist(k, #funs(myprog))
	  then 
	    (
	    print("Call "^k^"\n");
	    let
	      val myfun=getfun(k,#funs(myprog))
	      val funval =
	      		if mymethod=Static 
	        	then tracebody (myprog, mymethod, #body(myfun), myglobals, #vars(myfun))
			else tracebody (myprog, mymethod, #body(myfun), myglobals, (#vars(myfun))@myenv)
            in
	      if funval=Ok then (
	      			print("Return "^k^"\n");
				Ok
				)
		else funval
	    end
	    )
	  else Error("Function "^k^" is not defined")

and tracebody( myprog, mymethod, mystats, myglobals, myenv)=
	if mystats=nil then Ok
	  else 
	    let
	      val myresult=tracestat( myprog, mymethod, (hd mystats), myglobals, myenv)
	    in
	      if myresult=Ok then tracebody (myprog, mymethod, (tl mystats), myglobals, myenv)
	        else myresult
	    end;
	   
fun trace myprog mymethod=
	tracebody( myprog:MainDecl, mymethod:Method, #body(myprog), #vars(myprog), []);