项目介绍

将lisp风格的函数转换为C风格的函数
*                  LISP                      C
*
*   2 + 2          (add 2 2)                 add(2, 2)
*   4 - 2          (subtract 4 2)            subtract(4, 2)
*   2 + (4 - 2)    (add 2 (subtract 4 2))    add(2, subtract(4, 2))

涉及的知识点

该项目虽小,却向我们展示了编译器的一些东西: 词法分析,抽象语法树,语法树遍历等

词法分析

    public List<Token> tokens(String input) throws Exception {

        List<Token> tokenList = new ArrayList<Token>();
        int currentPos = 0;
        while (currentPos < input.length()) {

            char currentChar = input.charAt(currentPos);

            if ('(' == currentChar) {
                tokenList.add(new Token().setType("paren").setValue("("));
                currentPos++;
                continue;
            } else if (')' == currentChar) {
                tokenList.add(new Token().setType("paren").setValue(")"));
                currentPos++;
                continue;
            } else if (Character.isWhitespace(currentChar)) {
                currentPos++;
                continue;
            } else if (Character.isDigit(currentChar)) {
                StringBuilder digitsBuilder = new StringBuilder();
                while (Character.isDigit(currentChar)) {
                    digitsBuilder.append(currentChar);
                    currentChar = input.charAt(++currentPos);
                }
                tokenList.add(new Token().setType("number").setValue(digitsBuilder.toString()));
                continue;
            } else if (isAlphabet(currentChar)) {
                StringBuilder charsBuilder = new StringBuilder();
                while (isAlphabet(currentChar)) {
                    charsBuilder.append(currentChar);
                    currentChar = input.charAt(++currentPos);
                }
                tokenList.add(new Token().setType("name").setValue(charsBuilder.toString()));
                continue;
            } else {
                throw new Exception("I dont know what this character is: " + currentChar);
            }
        }
        return tokenList;
}

语法树

* 它的抽象语法树（AST）看起来或许是这样的：
*   {
*     type: 'Program',
*     body: [{
*       type: 'CallExpression',
 *       name: 'add',
 *       params: [{
 *         type: 'NumberLiteral',
 *         value: '2'
 *       }, {
 *         type: 'CallExpression',
 *         name: 'subtract',
 *         params: [{
 *           type: 'NumberLiteral',
 *           value: '4'
 *         }, {
 *           type: 'NumberLiteral',
 *           value: '2'
 *         }]
 *       }]
 *     }]
 *   }

项目github地址(Java实现版本)

https://github.com/AnoxiaTown/TheSuperTinyCompiler

JS中文版

https://github.com/starkwang/the-super-tiny-compiler-cn/blob/master/super-tiny-compiler-chinese.js

JS英文原版

https://github.com/jamiebuilds/the-super-tiny-compiler