AliasT/craftinginterpreters

实现一个脚本语言

craftinginterpreters

porting http://www.craftinginterpreters.com/scanning.html

重要过程方法

Method	Description	current
peek	返回当前字符	keep
peek_next	返回下一个字符	keep
advance	返回下一个字符	current + 1
expect	判断下一个字符是否为预期字符	current +

判断过程

语法分析

语法分析器从词法分析器获得一个由词法单元组成的串，并验证这个串可以由源语言的文法生成

BNF

parser

递归下降解析器

• Recursive descent is considered a top-down parser because it starts from the top or outermost grammar rule (here expression) and works its way down into the nested subexpressions before finally reaching the leaves of the syntax tree.

• A recursive descent parser is a literal translation of the grammar’s rules straight into imperative code.

• Each rule becomes a function.

• Each rule here only matches expressions at its precedence level or higher.

模式

1. 解释器模式
2. 访问者模式

  interface PastryVisitor {
    void visitBeignet(Beignet beignet);
    void visitCruller(Cruller cruller);
  }

  abstract class Pastry {
    abstract void accept(PastryVisitor visitor);
  }

  class Beignet extends Pastry {
    @Override
    void accept(PastryVisitor visitor) {
      visitor.visitBeignet(this);
    }
  }

  class Cruller extends Pastry {
    @Override
    void accept(PastryVisitor visitor) {
      visitor.visitCruller(this);
    }
  }