A small, but not quite correct, changes in CheckTop() and Compile() functions in presented above compiler allows recognition of the operator precedence in expressions:

word CheckTop(word L1) is word R:=nRight; word I:=pPoint[nStk]; while I< nPoint do if Right[Point[I]]=L1 then return nRight; end if Right[Point[I]]=0 then if R<nRight then Stop(); end R:=Point[I]; end I:=I+1; end return R; end word Compile() is Heap [ 66]:='p'; Heap [ 67]:='r'; Heap [ 68]:='g'; hFile := open(); pText := 0; nText := 0; nLine := 1; lFlag := 0; rFlag := 0; nCode := 0; nData :=16640; Emi1(0xE9); // jmp ? Emi2(0x00); Stk [0] := 1; // # pPoint[0] := 0; nStk := 0; Point [0] := nRight; nPoint := 1; Left [nLeft]:= 1; // # pRight[nLeft]:= nRight; AddSym(pProg); // Program AddSym(1); // # AddSym(0); nLeft := nLeft+1; Closure(pPoint[nStk]); while Stk[0]!=pProg do Scan (); Alter(); word R:=CheckTop(L); while R< nRight do Reduce(R); Shift (); R:=CheckTop(L); end Stk [nStk]:=L; Val [nStk]:=V; Shift(); end close(); Heap [ 66]:='c'; Heap [ 67]:='o'; Heap [ 68]:='m'; hFile:=create(); write(); close(); end

In contrast to the previous parser which fixed the error in the presence of the choice between shift and reduce, this parser performs reduce only if shift will lead to an empty state (i.e. state with no points).

To take into account the opertors precedence next changes in file c.def may be done:

Expr : 190 Expr Op1 Term | 0 Term ; Term : 190 Term Op2 Value | 0 Value ; Op1 : 0 plus | 0 minus ; Op2 : 0 star | 0 slash | 0 pct ;

Also rules for a function call may be simplified:

Call : 230 Fn lcb Params rcb | 230 Fn lcb rcb ; Params : 250 Params comma Expr | 250 Expr ; Fn : 260 fn ;

The modified parser also allow to remove the syntax sugar. For example semicolons, is, then and do keywords may be removed from grammar (and from programs).

If you change the rule for Expr as follow

Expr : 190 Value Op Expr | 0 Value ;

the expressions will be computed from right to left, i.e. as they are computed in original Tiny Context language.

And adding to CheckTop() function correct choice between shift and reduce. Unfortunately after that program exceeds one thousand lines of code limit:

word CanReduce(word Point1, word L1) is word nPoint1:=nPoint; AddPoint(nPoint1, Point1); word I:=nPoint1; while I< nPoint do if Right[Point[I]]=0 then word S:=Left[pLeft[Point[I]]]; word J:=0; while J< nLeft do word K:=pRight[J]; while Right[K]!=0 do if Right[K]=S then AddPoint(nPoint1, K+1); end K:=K+1; end J:=J+1; end end I:=I+1; end Closure(nPoint1); word J:=nPoint1; while J< nPoint do if Right[Point[J]]=L1 then nPoint:=nPoint1; return 0; end J:=J+1; end nPoint:=nPoint1; return 1; end word CheckTop(word L1) is word S:=0; word R:=nRight; word I:=pPoint[nStk]; while I< nPoint do if Right[Point[I]]=L1 then if R< nRight then Stop(); end S:=1; end if Right[Point[I]]=0 then if CanReduce(Point[I], L1)=0 then if S!=0 then Stop(); end if R< nRight then Stop(); end R:= Point[I]; end end I:=I+1; end if S=0 then if R=nRight then Stop(); end end return R; end

In some cases these changes allow to choice one of several reduces. For example, it will be possible to replace previously introduced terminal symbols type, var, array and fn with corresponding non-terminal symbols and rules for them:

Type : 270 char | 270 byte | 270 word ; Var : 280 name ; Array : 290 name ; Fn : 300 name ;

In the new actions 270, 280, 290 and 300 need to search for a name in the dictionary and verify that the symbol name are really Type, Var, Array or Fn. For example, when trying to access a simple variable as an array element error must be fixed.

After that scaner and parser are made fully independent (scaner no longer need access to the dictionary).

On modern computers, it is not very noticeable (but in DOSBox emulator are noticeable), but the compiler is running slow. At each shift step it build new state (set of points) and at each reduce step it destroy some states. To improve performance set of states and transitions table must be build once. After that work speed may be comparable to manually written recursive descent parser.

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