Hundreds of lines of code to implement a script interpreter

# Foreword recently, I am learning the compiling principle again , In fact, I reviewed it two years ago , At the beginning, it was to achieve the goal of passing `MySQL` Of `DDL` Generate `Python` in `sqlalchemy` Of `model`. Related articles are here ：[ Write a lexical analyzer by hand ](https://crossoverjie.top/2020/03/23/compilation/Lexer/)<!--more--> Although the relevant functions have been completed , But now it seems that the implementation is rough , And it only applies to lexical analysis ; So my goal this time is to use lexical analysis -> Syntax analysis -> Semantic analysis Finally, a fully functional script can be implemented " Language ".# The effect has now achieved some phased results , As shown in the figure below ： At present, it has the following basic functions ：- Variable declaration and assignment （ Only support int)- Quadratic operation （ Priority support ）- Syntax check - debug Pattern , You can print AST Interested friends can view the source code here ：[https://github.com/crossoverJie/gscript](https://github.com/crossoverJie/gscript) There is go Environment can also be installed and run .```shellgo get github.com/crossoverJie/gscriptgscript -h``` Or download the binary file directly to run ：[https://github.com/crossoverJie/gscript/releases](https://github.com/crossoverJie/gscript/releases)# The current version is implemented using go Compiling , Indeed, as the title says , The core code is less than 1k Line code , Of course, this is also related to the current simple functions . But the sparrow is small and has five internal organs , From the current version, some knowledge of compilation principles has been applied ： morphology 、 Syntax analysis . The basic implementation process is shown in the figure above ：- Parse the source code through the lexical analyzer token- Pass again token Derivation generates an abstract syntax tree （AST） - If the grammar is wrong , This step will throw a compilation failure , such as `2*(1+` One bracket is missing . Because there is no use similar to `ANTLR` This tool is used to help generate code （ Otherwise, there will be more functions ）, So the morphology 、 Grammar analysis is handwritten , There's not a lot of code , For friends who want to debug, you can directly view the source code . Lexical analyzer ：`token/token.go:39` parsers ：`syntax/syntax.go` There are some concepts involved , Such as finite state machine 、 Recursive descent algorithm and other knowledge points are not discussed in this article , In the future, the project will be reorganized after its functions are more perfect .# The final stage of planning is the pie drawing stage , The following functions will be added in the future ：- More basic types ,string/long And so on. .- Variable scope 、 function .- Even closures .- OOP There must be . After these features are implemented, it is also a " modern " The script language of , In the future, I will continue to update the interesting content in the process of learning and implementation . Source code address ：[https://github.com/crossoverJie/gscript](https://github.com/crossoverJie/gscript)