上面咱们来为计算器程序减少语句块性能，使得程序能够做批量运算，相似于程序语言中的代码块。
这次的代码以上一篇《递归向下算法实现Calc》的代码为根底编写，如果发现不相熟当下的内容能够回顾一下之前的篇章。
代码清单【go语言为例】package mainimport ( "fmt" "strconv" "io/ioutil" "./bklexer")type Node interface { GetValue() float64}type Block struct { statements []Node}func NewBlock() *Block { return &Block{}}func (block *Block) AddStatement(statement Node) { block.statements = append(block.statements, statement)}func (block *Block) Eval() { for i, statement := range block.statements { fmt.Printf("out[%d] = %f\n", i, statement.GetValue()) }}type Number struct { value float64}func NewNumber(token *BKLexer.Token) *Number { value, _ := strconv.ParseFloat(token.Source, 64) return &Number{value: value}}func (number *Number) GetValue() float64 { return number.value}type BinaryOpt struct { opt string lhs Node rhs Node}func NewBinaryOpt(token *BKLexer.Token, lhs Node, rhs Node) *BinaryOpt { return &BinaryOpt{opt: token.Source, lhs: lhs, rhs: rhs}}func (binaryOpt *BinaryOpt) GetValue() float64 { lhs, rhs := binaryOpt.lhs, binaryOpt.rhs switch binaryOpt.opt { case "+": return lhs.GetValue() + rhs.GetValue() case "-": return lhs.GetValue() - rhs.GetValue() case "*": return lhs.GetValue() * rhs.GetValue() case "/": return lhs.GetValue() / rhs.GetValue() } return 0}func parse(lexer *BKLexer.Lexer) *Block { block := NewBlock() token := lexer.NextToken() for token.TType == BKLexer.TOKEN_TYPE_NEWLINE { token = lexer.NextToken() } for token.TType != BKLexer.TOKEN_TYPE_EOF { statement := parse_binary_add(lexer) if statement == nil { return nil; } token = lexer.GetToken() if token.TType != BKLexer.TOKEN_TYPE_NEWLINE && token.TType != BKLexer.TOKEN_TYPE_EOF { return nil; } block.AddStatement(statement) for token.TType == BKLexer.TOKEN_TYPE_NEWLINE { token = lexer.NextToken() } } return block}func parse_binary_add(lexer *BKLexer.Lexer) Node { lhs := parse_binary_mul(lexer) if lhs == nil { return nil } token := lexer.GetToken() for token.Source == "+" || token.Source == "-" { lexer.NextToken() rhs := parse_binary_mul(lexer) if rhs == nil { return nil } lhs = NewBinaryOpt(token, lhs, rhs) token = lexer.GetToken() } return lhs}func parse_binary_mul(lexer *BKLexer.Lexer) Node { lhs := parse_number(lexer) if lhs == nil { return nil } token := lexer.GetToken() for token.Source == "*" || token.Source == "/" { lexer.NextToken() rhs := parse_number(lexer) if rhs == nil { return nil } lhs = NewBinaryOpt(token, lhs, rhs) token = lexer.GetToken() } return lhs}func parse_number(lexer *BKLexer.Lexer) Node { token := lexer.GetToken() if token.Name == "LPAR" { lexer.NextToken() expr := parse_binary_add(lexer) if expr == nil { return nil } token := lexer.GetToken() if token.Name != "RPAR" { return nil } lexer.NextToken() return expr } if token.Name == "NUMBER" { number := NewNumber(token) lexer.NextToken() return number } return nil}func main() { fmt.Println("Hello My Calc.") lexer := BKLexer.NewLexer() lexer.AddRule("\\d+\\.?\\d*", "NUMBER") lexer.AddRule("\\+", "PLUS") lexer.AddRule("-", "MINUS") lexer.AddRule("\\*", "MUL") lexer.AddRule("/", "DIV") lexer.AddRule("\\(", "LPAR") lexer.AddRule("\\)", "RPAR") lexer.AddIgnores("[ \\f\\t]+") lexer.AddIgnores("#[^\\r\\n]*") bytes, err := ioutil.ReadFile("../test.txt") if err != nil { fmt.Println("read faild") return } code := string(bytes) fmt.Println(code) lexer.Build(code) result := parse(lexer) if result == nil { fmt.Println("null result") return } result.Eval()}引入须要应用的包import ( "fmt" "strconv" "io/ioutil" "./bklexer")fmt 打印输出strconv 字符串转换io/ioutil 读取文件./bklexer 用于词法解析定义语句块构造体type Block struct { statements []Node}func NewBlock() *Block { return &Block{}}Block构造的成员statements用于存储每一条语句，咱们应用NewBlock办法实例这个构造。
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