摘要
程序開發行業中有很多種編程語言,每個程序員大概也都會一兩種,可你有沒有想過自己DIY一種語言呢,本文就帶你用.net DIY一種新語言--WawaSharp,我們將定義語法,實現詞法分析,建立語法樹,代碼生成幾個過程。
引言
創建 .NET Framework 語言編譯器
http://msdn.microsoft.com/zh-cn/magazine/cc136756.aspx
本文也是根據這篇帖子來的,只是在其基礎上支持了更多的語句和表達式,所以大家可以先看懂這篇文章,本文對這篇文章裏講到的東西也就不再詳細重複。我們要提高一個程序靈活性的時候常常把一些變量做成配置,這時候需求變了的話,修改一下配置就可以滿足需求了,可有時候配置不足以滿足需求的變化,所以一些更NB的程序,可以提供一個SDK及一套自定義語言讓使用者去二次開發,今天我們發明的語言就可以去當作這種場景下的自定義語言。另外一個目的就是和大家一起了解一下一個語言背後的故事,我們寫的文本代碼是如何變成可執行的程序的。
語法定義
<stmt> := var <ident> = <expr>
| <ident> = <expr>
| for <ident> = <expr> to <expr> do <stmt> end
| foreach <ident> in <expr> do <stmt> end
| if <expr> then <stmt> end
| read_int <ident>
| print <expr>
| <stmt> ; <stmt>
| append <expr> <expr>
<expr> := <string>
| <int>
| <arith_expr>
| <ident>
| match <expr> <expr>
| newsb
| len <expr>
<bin_expr> := <expr> <bin_op> <expr>
<bin_op> := + | - | * | / | == | eq
<ident> := <char> <ident_rest>*
<ident_rest> := <char> | <digit>
<int> := <digit>+
<digit> := 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
<string> := " <string_elem>* "
<string_elem> := <any char other than ">
語法有了,我們看下我們要實現的語言大概是什麼樣子,如下
var input = ""11|222|33|44|55"";
var arr = match input ""/d+|"";
var sb = newsb;
foreach item in arr do
print item;
var l = len item;
if l eq 2 then
var arr_ = match item ""/d"";
foreach item_ in arr_ do
append sb ""/r/n"";
append sb item_;
end;
end;
end;
print sb;
var arr = match input ""/d+|"";
var sb = newsb;
foreach item in arr do
print item;
var l = len item;
if l eq 2 then
var arr_ = match item ""/d"";
foreach item_ in arr_ do
append sb ""/r/n"";
append sb item_;
end;
end;
end;
print sb;
綜合語法定義和例子,我們可以看到,我們定義了string,bool,int,enumerable幾種數據類型,var,foreach,if,print,append等幾種語句,還有賦值,match,len,Equals,整形常量,字符串常量等幾種表達式。
詞法分析
把需求說清楚了,實現這個應該很簡單吧,就寫一個while循環,一個一個的讀取字符,每滿足一個token規則就放到list裏面一個就行了,僞碼如下
while (input.Peek() != -1)
{
char ch = (char)input.Peek();
if (char.IsWhiteSpace(ch))
{
//忽略空白字符
input.Read();
}
else if (char.IsLetter(ch) || ch == '_')
{
//取出標識符,以字母和下劃線組成
}
else if (ch == '"')
{
//取出字符串常量
}
else if (char.IsDigit(ch))
{
//取出數字常量
}
else switch (ch)
{
//取出單字符操作符,如+,-,*,/等
}
}
到此,我們有了一個IList<object>,裏面順序放着我們分析出來的文本塊兒。
語法分析
public abstract class Stmt{}
public abstract class Expr {}
public class DeclareVar : Stmt
{
public Expr Expr;
public string Ident;
}
public class Assign : Stmt
{
public Expr Expr;
public string Ident;
}
public class Sequence : Stmt
{
public Stmt First;
public Stmt Second;
}
public class Foreach : Stmt
{
public Stmt Body;
public string Ident;
public Expr IEnumerable;
}
public class If : Stmt {
public Stmt Body;
public Expr Condition;
}
public class StrLen : Expr
{
public Expr Input;
}
public class Match : Expr
{
public Expr Input;
public Expr Pattern;
}
public abstract class Expr {}
public class DeclareVar : Stmt
{
public Expr Expr;
public string Ident;
}
public class Assign : Stmt
{
public Expr Expr;
public string Ident;
}
public class Sequence : Stmt
{
public Stmt First;
public Stmt Second;
}
public class Foreach : Stmt
{
public Stmt Body;
public string Ident;
public Expr IEnumerable;
}
public class If : Stmt {
public Stmt Body;
public Expr Condition;
}
public class StrLen : Expr
{
public Expr Input;
}
public class Match : Expr
{
public Expr Input;
public Expr Pattern;
}
意思就是我們要把token序列轉換成一個由上述這些對象組成的一顆樹,差不多是二叉樹,這一步叫語法分析,據說要多複雜有多複雜,但咱們這裏還算比較簡單,也是一個while循環,比如碰到if語句,就根據語法定義if <expr> then <stmt> end,下一個token應該是個表達式,表示if語句的條件,那麼就繼續出一個表達式作爲if語句的Condition樹形,再往後要有一個then,再往後是一個語句,解析出一條完整語句,作爲if的Body樹形,完了最後以一個end結尾,大概僞碼如下吧。
private Stmt ParseStmt() {
if (tokens[index].Equals("print")) {
index++;
var print = new Print();
print.Expr = ParseExpr();
result = print;
}
else if (tokens[index].Equals("append"))
{
index++;
var append = new Append();
append.Buider = ParseExpr();
append.ToAppend = ParseExpr();
}
else if (tokens[index].Equals("var")) {}
else if (tokens[index].Equals("foreach")) {}
else if (tokens[index].Equals("if")) {}
else{ thr ex;}
if (index < tokens.Count && tokens[index] == Scanner.Semi) {
index++;
if (index < tokens.Count &&!tokens[index].Equals("end")) {
var sequence = new Sequence();
sequence.First = result;
sequence.Second = ParseStmt();
result = sequence;
}
}
}
private Expr ParseExpr() {
if (tokens[index] is StringBuilder) {//StringLiteral}
else if (tokens[index] is int) {//IntLiteral}
else if (tokens[index] is string) {
string value = (string)tokens[index];
if (value.Equals("match")) {//Match}
else if (value.Equals("newsb")) {//Builder}
else if (value.Equals("len")) {//Strlen}
}
}
if (tokens[index].Equals("print")) {
index++;
var print = new Print();
print.Expr = ParseExpr();
result = print;
}
else if (tokens[index].Equals("append"))
{
index++;
var append = new Append();
append.Buider = ParseExpr();
append.ToAppend = ParseExpr();
}
else if (tokens[index].Equals("var")) {}
else if (tokens[index].Equals("foreach")) {}
else if (tokens[index].Equals("if")) {}
else{ thr ex;}
if (index < tokens.Count && tokens[index] == Scanner.Semi) {
index++;
if (index < tokens.Count &&!tokens[index].Equals("end")) {
var sequence = new Sequence();
sequence.First = result;
sequence.Second = ParseStmt();
result = sequence;
}
}
}
private Expr ParseExpr() {
if (tokens[index] is StringBuilder) {//StringLiteral}
else if (tokens[index] is int) {//IntLiteral}
else if (tokens[index] is string) {
string value = (string)tokens[index];
if (value.Equals("match")) {//Match}
else if (value.Equals("newsb")) {//Builder}
else if (value.Equals("len")) {//Strlen}
}
}
最終,我們會形成一個語法樹,比如我們示例代碼的分析結果如下
[Sequence]
|First:
| |[DeclareVar]
| | |Ident:input
| | |Expr:
| | | |<StringLiteral>:"11|222|33|44|55"
|Second:
| |[Sequence]
| | |First:
| | | |[DeclareVar]
| | | | |Ident:arr
| | | | |Expr:
| | | | | |<Match>:
| | | | | | |Input:
| | | | | | | |<Variable>:input
| | | | | | |Pattern:
| | | | | | | |<StringLiteral>:"/d+|"
| | |Second:
| | | |[Sequence]
| | | | |First:
| | | | | |[DeclareVar]
| | | | | | |Ident:sb
| | | | | | |Expr:
| | | | | | | |[Builder]
| | | | |Second:
| | | | | |[Sequence]
| | | | | | |First:
| | | | | | | |<Foreach>:item
| | | | | | | | |IEnumerable:
| | | | | | | | | |<Variable>:arr
| | | | | | | | |Body:
| | | | | | | | | |[Sequence]
| | | | | | | | | | |First:
| | | | | | | | | | | |[Print]
| | | | | | | | | | | | |Expr:
| | | | | | | | | | | | | |<Variable>:item
| | | | | | | | | | |Second:
| | | | | | | | | | | |[Sequence]
| | | | | | | | | | | | |First:
| | | | | | | | | | | | | |[DeclareVar]
| | | | | | | | | | | | | | |Ident:l
| | | | | | | | | | | | | | |Expr:
| | | | | | | | | | | | | | | |<StrLen>:
| | | | | | | | | | | | | | | | |Input:
| | | | | | | | | | | | | | | | | |<Variable>:item
| | | | | | | | | | | | |Second:
| | | | | | | | | | | | | |<If>:
| | | | | | | | | | | | | | |Condition:
| | | | | | | | | | | | | | | |<BinExpr>:Eq
| | | | | | | | | | | | | | | | |left:
| | | | | | | | | | | | | | | | | |<Variable>:l
| | | | | | | | | | | | | | | | |Right:
| | | | | | | | | | | | | | | | | |<IntLiteral>:2
| | | | | | | | | | | | | | |Body:
| | | | | | | | | | | | | | | |[Sequence]
| | | | | | | | | | | | | | | | |First:
| | | | | | | | | | | | | | | | | |[DeclareVar]
| | | | | | | | | | | | | | | | | | |Ident:arr_
| | | | | | | | | | | | | | | | | | |Expr:
| | | | | | | | | | | | | | | | | | | |<Match>:
| | | | | | | | | | | | | | | | | | | | |Input:
| | | | | | | | | | | | | | | | | | | | | |<Variable>:item
| | | | | | | | | | | | | | | | | | | | |Pattern:
| | | | | | | | | | | | | | | | | | | | | |<StringLiteral>:"/d"
| | | | | | | | | | | | | | | | |Second:
| | | | | | | | | | | | | | | | | |<Foreach>:item_
| | | | | | | | | | | | | | | | | | |IEnumerable:
| | | | | | | | | | | | | | | | | | | |<Variable>:arr_
| | | | | | | | | | | | | | | | | | |Body:
| | | | | | | | | | | | | | | | | | | |[Sequence]
| | | | | | | | | | | | | | | | | | | | |First:
| | | | | | | | | | | | | | | | | | | | | |[Append]:
| | | | | | | | | | | | | | | | | | | | | | |Buider:
| | | | | | | | | | | | | | | | | | | | | | | |<Variable>:sb
| | | | | | | | | | | | | | | | | | | | | | |ToAppend:
| | | | | | | | | | | | | | | | | | | | | | | |<StringLiteral>:""
| | | | | | | | | | | | | | | | | | | | |Second:
| | | | | | | | | | | | | | | | | | | | | |[Append]:
| | | | | | | | | | | | | | | | | | | | | | |Buider:
| | | | | | | | | | | | | | | | | | | | | | | |<Variable>:sb
| | | | | | | | | | | | | | | | | | | | | | |ToAppend:
| | | | | | | | | | | | | | | | | | | | | | | |<Variable>:item_
| | | | | | |Second:
| | | | | | | |[Print]
| | | | | | | | |Expr:
| | | | | | | | | |<Variable>:sb
|First:
| |[DeclareVar]
| | |Ident:input
| | |Expr:
| | | |<StringLiteral>:"11|222|33|44|55"
|Second:
| |[Sequence]
| | |First:
| | | |[DeclareVar]
| | | | |Ident:arr
| | | | |Expr:
| | | | | |<Match>:
| | | | | | |Input:
| | | | | | | |<Variable>:input
| | | | | | |Pattern:
| | | | | | | |<StringLiteral>:"/d+|"
| | |Second:
| | | |[Sequence]
| | | | |First:
| | | | | |[DeclareVar]
| | | | | | |Ident:sb
| | | | | | |Expr:
| | | | | | | |[Builder]
| | | | |Second:
| | | | | |[Sequence]
| | | | | | |First:
| | | | | | | |<Foreach>:item
| | | | | | | | |IEnumerable:
| | | | | | | | | |<Variable>:arr
| | | | | | | | |Body:
| | | | | | | | | |[Sequence]
| | | | | | | | | | |First:
| | | | | | | | | | | |[Print]
| | | | | | | | | | | | |Expr:
| | | | | | | | | | | | | |<Variable>:item
| | | | | | | | | | |Second:
| | | | | | | | | | | |[Sequence]
| | | | | | | | | | | | |First:
| | | | | | | | | | | | | |[DeclareVar]
| | | | | | | | | | | | | | |Ident:l
| | | | | | | | | | | | | | |Expr:
| | | | | | | | | | | | | | | |<StrLen>:
| | | | | | | | | | | | | | | | |Input:
| | | | | | | | | | | | | | | | | |<Variable>:item
| | | | | | | | | | | | |Second:
| | | | | | | | | | | | | |<If>:
| | | | | | | | | | | | | | |Condition:
| | | | | | | | | | | | | | | |<BinExpr>:Eq
| | | | | | | | | | | | | | | | |left:
| | | | | | | | | | | | | | | | | |<Variable>:l
| | | | | | | | | | | | | | | | |Right:
| | | | | | | | | | | | | | | | | |<IntLiteral>:2
| | | | | | | | | | | | | | |Body:
| | | | | | | | | | | | | | | |[Sequence]
| | | | | | | | | | | | | | | | |First:
| | | | | | | | | | | | | | | | | |[DeclareVar]
| | | | | | | | | | | | | | | | | | |Ident:arr_
| | | | | | | | | | | | | | | | | | |Expr:
| | | | | | | | | | | | | | | | | | | |<Match>:
| | | | | | | | | | | | | | | | | | | | |Input:
| | | | | | | | | | | | | | | | | | | | | |<Variable>:item
| | | | | | | | | | | | | | | | | | | | |Pattern:
| | | | | | | | | | | | | | | | | | | | | |<StringLiteral>:"/d"
| | | | | | | | | | | | | | | | |Second:
| | | | | | | | | | | | | | | | | |<Foreach>:item_
| | | | | | | | | | | | | | | | | | |IEnumerable:
| | | | | | | | | | | | | | | | | | | |<Variable>:arr_
| | | | | | | | | | | | | | | | | | |Body:
| | | | | | | | | | | | | | | | | | | |[Sequence]
| | | | | | | | | | | | | | | | | | | | |First:
| | | | | | | | | | | | | | | | | | | | | |[Append]:
| | | | | | | | | | | | | | | | | | | | | | |Buider:
| | | | | | | | | | | | | | | | | | | | | | | |<Variable>:sb
| | | | | | | | | | | | | | | | | | | | | | |ToAppend:
| | | | | | | | | | | | | | | | | | | | | | | |<StringLiteral>:""
| | | | | | | | | | | | | | | | | | | | |Second:
| | | | | | | | | | | | | | | | | | | | | |[Append]:
| | | | | | | | | | | | | | | | | | | | | | |Buider:
| | | | | | | | | | | | | | | | | | | | | | | |<Variable>:sb
| | | | | | | | | | | | | | | | | | | | | | |ToAppend:
| | | | | | | | | | | | | | | | | | | | | | | |<Variable>:item_
| | | | | | |Second:
| | | | | | | |[Print]
| | | | | | | | |Expr:
| | | | | | | | | |<Variable>:sb
我在Stmt和Expr類各定義了個ToString方法來用文本顯示這棵樹,最終結果類似上面這樣的顯示,雖然不是很美,但意思能表達出來,我們的分析結果確實是棵樹,CodeDom有樹,表達式樹有樹,咱們的WawaSharp也得有樹。
看到這裏,大家可以稍微休息休息,目前爲止,我們還沒碰到什麼新鮮的,就是一些while語句和一些字符串拆分邏輯,下一篇會講到代碼生成,就是根據這棵樹生成可執行的IL代碼,有趣的是生成IL代碼後還能用Reflector反編譯成c#和vb代碼,呵呵。