【COMPILER 语法分析器 代码清单】

import scannerclass as sc
class ExprNode(object):     ## 语法树节点类
    def __init__(self,item):        ## item 表示符号类型Token_Type
        self.item = item #表示对应的元素
        if self.item == sc.Token_Type.PLUS or self.item == sc.Token_Type.MINUS or 
                self.item == sc.Token_Type.MUL or self.item == sc.Token_Type.DIV or 
                self.item == sc.Token_Type.POWER:
            # 运算符 - 两个孩子
            self.left=None
            self.right=None
        elif self.item == sc.Token_Type.FUNC:
            self.FuncPtr = None
            self.center = None      ## 一个孩子
        self.value = None       ## 传入的所有类型都有value
    def __str__(self):      ## 叶子节点
        return str(self.item)  #print 一个 Node 类时会打印 __str__ 的返回值

    def GetExprValue(self):
        if self.item == sc.Token_Type.PLUS:
            self.value = self.right.value + self.left.value
        elif self.item == sc.Token_Type.MINUS:
            self.value = self.left.value - self.right.value
        elif self.item == sc.Token_Type.MUL:
            self.value = self.left.value * self.right.value
        elif self.item == sc.Token_Type.DIV:
            self.value = self.left.value / self.right.value
        elif self.item == sc.Token_Type.POWER:
            self.value = self.left.value ** self.right.value
        elif self.item == sc.Token_Type.FUNC:
            self.value = self.FuncPtr(self.center.value)
        return self.value

import scannerclass as sc
class ExprNode(object):     ## 语法树节点类
    def __init__(self,item):        ## item 表示符号类型Token_Type
        self.item = item #表示对应的元素
        if self.item == sc.Token_Type.PLUS or self.item == sc.Token_Type.MINUS or 
                self.item == sc.Token_Type.MUL or self.item == sc.Token_Type.DIV or 
                self.item == sc.Token_Type.POWER:
            # 运算符 - 两个孩子
            self.left=None
            self.right=None
        elif self.item == sc.Token_Type.FUNC:
            self.FuncPtr = None
            self.center = None      ## 一个孩子
        self.value = None       ## 传入的所有类型都有value
    def __str__(self):      ## 叶子节点
        return str(self.item)  #print 一个 Node 类时会打印 __str__ 的返回值

    def GetExprValue(self):
        if self.item == sc.Token_Type.PLUS:
            self.value = self.right.value + self.left.value
        elif self.item == sc.Token_Type.MINUS:
            self.value = self.left.value - self.right.value
        elif self.item == sc.Token_Type.MUL:
            self.value = self.left.value * self.right.value
        elif self.item == sc.Token_Type.DIV:
            self.value = self.left.value / self.right.value
        elif self.item == sc.Token_Type.POWER:
            self.value = self.left.value ** self.right.value
        elif self.item == sc.Token_Type.FUNC:
            self.value = self.FuncPtr(self.center.value)
        return self.value

import scannerfunc as sf
import parserfunc as pf

file_name = 'test.txt'
scanner = sf.scanner(file_name)
parser = pf.Parsef(scanner)
parser.Parser()

原本的测试文件是FOR T FROM 0 TO 2*PI STEP PI/50 DRAW(COS(T),SIN(T));
但是出现一点错误：COS（T）、和SIN(T)没能正确识别。
由于时间来不及了，就简化为常数。

FOR T FROM 0 TO 2*PI STEP PI/50 DRAW(COS(30),COS(45));