I set out to write a calculator that could produce numerical results from text input.
I had played with various Desktop Calculators and had become interested in how one might be programmed.
I had also just learned CDC 6500 assembly language programming under the guidance of Dave Dodson.
I can remember spending a vacation with family writing code on paper as I tried various representations without quite discovering parsing theory on my own.
I keypunched the calculator when I returned to school. I started debugging it but also became aware of weaknesses in my approach.
I later wrote a PL/1 Compiler in assembler and was much more successful after this false start.