jc/vm/interp.jai

Interp :: struct {
   allocator: Allocator;

   symbols:  kv.Kv(string, *Interp_Value);
   toplevel: []*Node;
}

Interp_Value :: struct {
   kind: Kind;
   union {
      b: bool;
      i: s64;
      u: u64;
      f: float64;
      s: string;
   }

   Kind :: enum {
      none;
      nil;
      bool;
      int;
      float;
      string;
   }
}

init :: (i: *Interp, allocator: Allocator) {
   value_nil = make_interp_value(i, .nil);

   value_true   = make_interp_value(i, .bool);
   value_true.b = true;

   value_false   = make_interp_value(i, .bool);
   value_false.b = false;
}

interp_program :: (i: *Interp) {
   for i.toplevel if it.kind == {
      case .variable;
         var  := it.(*Node_Var);
         sym  := var.symbol.(*Node_Symbol);
         basic.assert(!kv.exists(*i.symbols, sym.str), "redeclaring symbol '%'", sym.str); // @errors

         value := value_nil;
         if var.value_expr != null {
            value = interp_expr(i, var.value_expr);
            basic.assert(value != null); // @errors
         }

         kv.set(*i.symbols, sym.str, value);

      case .print;
         print := it.(*Node_Print);
         expr  := interp_expr(i, print.expr);
         if expr == null continue;

         if expr.kind == {
            case .none; // do nothing
            case .nil;    basic.print("nil");
            case .bool;   basic.print("%", expr.b);
            case .int;    basic.print("%", expr.i);
            case .float;  basic.print("%", expr.f);
            case .string; basic.print("%", expr.s);
            case; basic.assert(false, "unhandled interp value kind: %", expr.kind);
         }

         basic.print("\n");

      case;
         basic.assert(false, "unhandled node kind: %", it.kind); // @errors
   }
}

interp_expr :: (i: *Interp, expr: *Node) -> *Interp_Value {
   if expr.kind == {
      case .unary;
         do_unop :: (code: Code) #expand {
            if rhs.kind == {
               case .int;
                  right := rhs.i;
                  res.i = #insert,scope() code;
               case .float;
                  right := rhs.f;
                  res.f = #insert,scope() code;
               case;
                  basic.assert(false, "cannot use unary operator '%' on values of type '%'", un.op, rhs.kind);
            }
         }

         un  := expr.(*Node_Unary);
         rhs := interp_expr(i, un.right);
         res := make_interp_value(i, rhs.kind);
         if un.op.kind == {
            case .plus;  do_unop(#code ifx right < 0 then -right else right);
            case .minus; do_unop(#code -right);
            case; basic.assert(false, "unhandled unary operator '%'", un.op.str); // @errors
         }

         return res;

      case .binary;
         bin := expr.(*Node_Binary);
         lhs := interp_expr(i, bin.left);
         rhs := interp_expr(i, bin.right);
         basic.assert(lhs.kind == rhs.kind, "type mismatch % vs. %", lhs.kind, rhs.kind); // @errors

         do_binop :: (code: Code) #expand {
            if lhs.kind == {
               case .int;
                  left  := lhs.i;
                  right := rhs.i;
                  res.i = #insert,scope() code;
               case .float;
                  left  := lhs.f;
                  right := rhs.f;
                  res.f = #insert,scope() code;
               case;
                  basic.assert(false, "cannot use binary operator '%' on values of type '%'", bin.op, lhs.kind);
            }
         }

         res := make_interp_value(i, lhs.kind);
         if bin.op.kind == {
            case .plus;    do_binop(#code left + right);
            case .minus;   do_binop(#code left - right);
            case .star;    do_binop(#code left * right);
            case .f_slash;
               basic.assert(rhs.i != 0, "divide by zero"); // @errors
               do_binop(#code left / right);
            case .percent;
               basic.assert(lhs.kind == .int, "cannot use binary operator '%%' on values of type '%'", lhs.kind);
               res.i = lhs.i % rhs.i;

            case; basic.assert(false, "unhandled binary operator '%'", bin.op.str);
         }

         return res;

      case .symbol;
         sym := expr.(*Node_Symbol);

         value, ok := kv.get(*i.symbols, sym.str);
         basic.assert(ok, "use of undeclared symbol '%'", sym.str); // @errors
         return value;

      case .literal;
         lit := expr.(*Node_Literal);
         if lit.value_kind == {
            case .int;
               value := make_interp_value(i, .int);
               value.i = lit.i;
               return value;

            case .float;
               value := make_interp_value(i, .float);
               value.f = lit.f;
               return value;

            case; basic.assert(false, "unhandled literal kind: %", lit.value_kind); // @errors
         }

      case; basic.assert(false, "unhandled node kind: %", expr.kind); // @errors
   }

   return null;
}

#scope_file;

value_nil:   *Interp_Value;
value_true:  *Interp_Value;
value_false: *Interp_Value;

make_interp_value :: (i: *Interp, kind: Interp_Value.Kind) -> *Interp_Value {
   value := mem.request_memory(Interp_Value,, allocator = i.allocator);
   value.kind = kind;
   return value;
}