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设计思路：
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设计记号：词法分析器读取一个序列并根据构词规则把序列转化为记号流
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定义一个字典：把所有符合一个模式的保留字、常量名、参数名、函数名等放进字典。字典是个数组，其元素的类型和记号的类型相同
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设计程序的结构，具体见下面的代码
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用Pycharm写了三个.py文件：
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scannerclass.py - 构造枚举类 记号类 符号表
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scannerfunc.py - 构造词法分析器类
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scannermain.py - 完成I/O流
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输入流是序列（存储在.txt文本），输出流是“字典”（一个个识别好的记号对象）
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测试文本序列（1）：
FOR T FROM 0 TO 2*PI STEP PI/50 DRAW(COS(t),sin(t)); -
测试文本序列（2）：
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//------------------This is zhushi!!------------------------
ORIGIN IS (100,300); // Sets the offset of the origin
ROT IS 0; // Set rotation Angle.
SCALE IS (1,1); // Set the abscissa and ordinate scale.
FOR T FROM 0 TO 200 STEP 1 DRAW (T,0); // The trajectory of the x-coordinate.
FOR T FROM 0 TO 150 STEP 1 DRAW (0,-T); // The trajectory of the y-coordinate.
FOR T FROM 0 TO 120 STEP 1 DRAW (T,-T); // The trajectory of the function f[t]=t.
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设计思路：
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设计函数绘图语言的文法，使其适合递归下降分析；
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设计语法树的结构，用于存放表达式的语法树；
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设计递归下降子程序，分析句子并构造表达式的语法树；
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设计测试程序和测试用例，检验分析器是否正确。
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消除无二义/无左递归完整的EBNF文法：
- 表达式的语法树：
- 用Pycharm写了三个.py文件：
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parserclass.py - 构造语法树节点类
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parserfunc.py - 构造语法分析器类
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parsermain.py - 完成I/O流
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输入流是词法分析器得到的记号流，输出流是语法树
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测试文本序列（1）
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FOR T FROM 0 TO 2*PI STEP PI/50 DRAW(COS(T),SIN(T));
+ 测试文本序列 (2)
//------------------This is zhushi!!------------------------
ORIGIN IS (100,300); // Sets the offset of the origin
ROT IS 0; // Set rotation Angle.
SCALE IS (1,1); // Set the abscissa and ordinate scale.
FOR T FROM 0 TO 200 STEP 1 DRAW (T,0); // The trajectory of the x-coordinate.
FOR T FROM 0 TO 150 STEP 1 DRAW (0,-T); // The trajectory of the y-coordinate.
FOR T FROM 0 TO 120 STEP 1 DRAW (T,-T); // The trajectory of the function f[t]=t.
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设计思路：
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将语法分析器并入绘图功能
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继承语法分析器覆盖重写
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用Pycharm写了一个.py文件：
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semanticfunc.py - 继承语法分析器并入绘制功能
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semanticmain.py - 解释器主函数入口 //与语法分析器入门用的同一个入口
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输入流是语法分析器得到的语法树，输出流是绘制的图像
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测试文本序列：
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//----------------测试程序1：分别测试------------------------
ORIGIN IS (100,300); // Sets the offset of the origin
ROT IS 0; // Set rotation Angle.
SCALE IS (1,1); // Set the abscissa and ordinate scale.
FOR T FROM 0 TO 200 STEP 1 DRAW (T,0); // The trajectory of the x-coordinate.
FOR T FROM 0 TO 150 STEP 1 DRAW (0,-T); // The trajectory of the y-coordinate.
FOR T FROM 0 TO 120 STEP 1 DRAW (T,-T); // The trajectory of the function f[t]=t.
FOR T FROM 0 TO 2*PI STEP PI/50 DRAW(COS(T),SIN(T));
//---------测试程序2----------
ORIGIN IS (20, 200);
ROT IS 0;
SCALE IS (40, 40);
FOR T FROM 0 TO 2*PI STEP PI/50 DRAW (T, -SIN(T));
ORIGIN IS (20, 240);
FOR T FROM 0 TO 2*PI STEP PI/50 DRAW (T, -SIN(T));
ORIGIN IS (20, 280);
FOR T FROM 0 TO 2*PI STEP PI/50 DRAW (T, -SIN(T));
//-----------------测试程序3--------------
ORIGIN IS (380, 240);
SCALE IS (80, 80/3);
ROT IS PI/2+0*PI/3 ;
FOR T FROM -PI TO PI STEP PI/50 DRAW (COS(T), SIN(T));
ROT IS PI/2+2*PI/3;
FOR T FROM -PI TO PI STEP PI/50 DRAW (COS(T), SIN(T));
ROT IS PI/2-2*PI/3;
FOR T FROM -PI TO PI STEP PI/50 DRAW (COS(T), SIN(T));
//-------------------测试程序4-------------
ORIGIN IS(580, 240);
SCALE IS (80, 80);
ROT IS 0;
FOR T FROM 0 TO 2*PI STEP PI/50 DRAW(COS(T),SIN(T));
FOR T FROM 0 TO PI*20 STEP PI/50 DRAW((1-1/(10/7))*COS(T)+1/(10/7)*COS(-T*((10/7)-1)),(1-1/(10/7))*SIN(T)+1/(10/7)*SIN(-T*((10/7)-1)));
//-------------------测试程序5------------
//------------ 函数复杂度图形：-----------
ROT IS 0; -- 不旋转
ORIGIN IS (50, 400); -- 设置新原点（距系统默认原点的偏移量）
SCALE IS (2,1); -- 设置比例
FOR T FROM 0 TO 300 STEP 1 DRAW (T,0); -- 横坐标
FOR T FROM 0 TO 300 STEP 1 DRAW (0,-T); -- 纵坐标
SCALE IS (2,1); -- 设置比例
FOR T FROM 0 TO 300 STEP 1 DRAW (T,-T); -- 函数F(T)=T的轨迹
SCALE IS (2,0.1); -- 设置比例
FOR T FROM 0 TO 55 STEP 1 DRAW (T,-T*T); -- 函数F(T)=T*T的轨迹
SCALE IS (10,5); -- 设置比例
FOR T FROM 0 TO 60 STEP 1 DRAW (T,-SQRT(T)); -- 函数F(T)=SQRT(T)的轨迹
SCALE IS (20,0.1); -- 设置比例
FOR T FROM 0 TO 8 STEP 0.1 DRAW (T,-EXP(T)); -- 函数F(T)=EXP(T)的轨迹
SCALE IS (2,20); -- 设置比例
FOR T FROM 0 TO 300 STEP 1 DRAW (T,-LN(T)); -- 函数F(T)=LN(T)的轨迹