How to develop compiler without compiler writing tools

My teacher gave this question ( how to develop compilers without compiler writing tools ). I searched for it but I did not find anything. So, If anyone have any idea about this please help me. I found so many information about developing compiler with writing tools but I found nothing when I searched for without compiler writing tools.

Thank you in advance.

Solution

With:

Hand-written scanner (large switch statement), and
Recursive descent parser.

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