Let’s Create An Interpreter In Go Go Conference 2017 Autumn 

Self Introduce ● Kenshi Kamata ● @knsh14 (twitter, GitHub) ● KLab inc. ○ Unity3d Editor Extension ○ Create Facebook Instant Game 

What I did? ● Read Writing An Interpreter In Go ○ https://interpreterbook.com/ ● Actually Create An Interpreter ● Create An Interpreter in about 1400 lines！ ○ Included test code, about 2500 lines 

DEMO let x = 0; let array = [0, 10, 20, 30, 40]; array[1]; let fib = fn(x) { if(x == 0) { 0; } else { if (x == 1) { 1;} else { fib(x-1) + fib(x-2);}}}; let loop = fn(i, max, f) { if(i == max){return 0;} f(); loop(i +1, max, f);}; let p = fn() { puts(“hello world”);}; 

Why I did? ● I want to create self-produced Language ● Tried “Writing An Interpreter In C” book ○ but it was so hard and gave up ● I heard good book by Go is released! so I decided to try again. 

Specification ● Monkey Language ● Integer, Boolean, String, Function ● Array, Hash ● Able to use if statement ○ No For loop ● No yacc, use self-implemented Lexer and Parser 

How long Until Finished ● About 1 month ● some finished in one week ● Most of people can finish within 1.5 month 

Hard Part ● Parser logic was hard ● Pratt Parser ● google 演算子順位法 in japanese 

What I learned ● Fun to make Language by myself! ● Understand AST a little through Parser Chapter ● Not Following Go Practice in Some part 

Understand AST ● Build AST in Parser Chapter ● Wrote A tool to check cyclomatic complexity with AST in past but it was poor code ● I must be able to write better code after reading Parser chapter 

Not Following Go Practice ● Return Error ASAP / Return Error type ● Not good practice in Interpreter ● Example Code in Monkey ● Actually, go/parser has similar code ● https://golang.org/src/go/parser/parser.go filter by “p.error”, you can see no handling error 

Not following Go practice ● Don’t want to stop processing ● For user experience, Parse to End then show all error messages ● append to error string list, so not need to handle error at the time 

Finally ● Great feeling to exec code on my own interpreter ○ different feeling to playing my own game ● Good for Japanese people ○ Easy English ○ Understand by English after Understanding by Code 

Next is Your Turn!!