public Void Visit(IfStatement s, CompilerContext env)
        {
            s.condition.Accept(compileExpr, env);
            var brfPosition = env.Allocate();

            s.consequent.Accept(this, env);

            var braPosition = env.Allocate();

            var elsePosition = env.Line();

            s.consequent.Accept(this, env);

            var fiPosition = env.Line();

            env.EmitAt(brfPosition, new Instruction(Instruction.OPCODE.BRF, elsePosition));
            env.EmitAt(braPosition, new Instruction(Instruction.OPCODE.BRA, fiPosition));

            return Void.Instance;
        }