Context-Free Grammar compiler design and implementation-Q & A with a student

Context-Free Grammar compiler design and implementation-Q & A with a student

This article is from a QQ chat Q & A record with a classmate I don't know. I hope I can help those who read the articles I wrote to make the compiler but cannot understand it.

The release of this article has been approved and supported by "I want to ask some questions". Thank you!

PS: the bold words are not me bold! What is wlw! Let's download the PDF version here. The format is better.

Some questions: 9:15:17 Hello ~

Nulshunde: 15: 21 Hi!

Nulshunde: 15: 26 What is it called?

Some questions: 9:15:51 Well, you can ask me some questions ~

Some questions: 9:16:07 I have been working on an experimental course on compilation principles recently ~ Then ~~ No ..

Some questions: 9:16:22 I would like to ask how to create a syntax tree from the ll1 analysis table ..

Nulshunde: 17: 14 This problem is too long.

Nulshunde: 17: 20 Have you read my blog?

Some questions: 9:17:20 Amount...

Some questions: 9:17:50 I saw it .. I don't know much about it ..

Nulshunde: 18: 28 Ll1Can I understand the structure of the analysis table?

Some questions: 9:25:35 Well, this can

Some questions: 9:28:12 But I don't quite understand the relationship between ll1 analysis table and syntax tree ..

Null9: 28: 27

Nulshunde: 28: 31 Read this section

Nulshunde: 29: 17 We recommend that you start by understanding the expression syntax tree.

Nulshunde: 31: 16 Can the Grammar be understood?

Some questions: 9:31:53 Yes ..

Some questions: 9:31:58 Looking at it ..

Nulshunde: 32: 12 Is that OK or not?

Some questions: 9:32:32 Yes...

Null9: 32: 38 Do you have an expression syntax?

Null9: 32: 39 That's it.

Null9: 32: 39 <Expression >::= <multiply> <plusopt>; <Plusopt >:: = "+" <multiply> | "-" <multiply> | NULL; <Multiply >::=< unit> <multiplyopt>; <Multiplyopt >:: = "*" <unit> | "/" <unit> | NULL; <Unit>: = Number | "(" <expression> ")";

Some questions: 9:33:58 This can be understood .. But it's a little different from the book.

Nulshunde: 34: 17 What's different?

Some questions: 9:34:43 It doesn't matter. It's a bit different in the way of narration...

Nulshunde: 34: 54 The structure must be the same.

Nulshunde: 35: 06 Grammar is the foundation of everything

Some questions: 9:48:16 .. In fact, I mean, there is now a syntax and a program, there are various first sets and follow sets of this syntax, ll1 analysis table, and then how to draw the syntax tree of the program...

Nulshunde: 49: 14 Draw the syntax tree of the program. It is enough to have this program and ll1 analysis table.

Nulshunde: 49: 49 4.1 ll1Analysis Process

Nulshunde: 49: 53 Can this part not be understood?

Some questions: 9:50:36 Let's take a look...

Nulshunde: 51: 22 The first step is to assume that the program has no syntax errors, then the entire program corresponds to the Start Node of the grammar.

Some questions: 9:51:36 Well

Nulshunde: 51: 49 The Start Node has one or more candidate types.

Nula9: 52: 03 The candidate formula is determined by the ll1 analysis table.

Some questions: 9:52:23 What is the starting node of the syntax tree?

Nulshunde: 52: 28 Pair

Some questions: 9:52:32 Nun

Nulshunde: 52: 44 The root node represents the entire program.

Some questions: 9:52:47 Well

Null9: 53: 00 Let me use expression as an example.

Some questions: 9:53:04 Well

Nulshunde: 54: 06 ExpressionAs the root node, the first word [(19 + 18) * (19-18)] is "("

Some questions: 9:54:18 Well

Null9: 54: 48 ExpressionThis syntax tree node type corresponds to "(" this word type corresponds to the candidate formula in the ll1 analysis table is <multiply> <plusopt>

Nulshunde: 55: 06 Therefore, the expression root node generates the multiply and plusopt leaf nodes.

Nulshunde: 55: 11 No, it's a subnode.

Some questions 9:55:23 Nun

Nulshunde: 55: 43 Then we continue to analyze multiply.

Nulshunde: 56: 16 MultiplyThis syntax tree node corresponds to "(" the candidate formula in the ll1 analysis table is <unit> <multiplyopt>

Some questions: 9:56:24 Well

Nulshunde: 56: 29 Therefore, multiply generates the unit and multiplyopt subnodes.

Null9: 57: 08 Then, let's look at the unit and (", in the ll1 analysis table corresponding to the candidate formula [" ("<expression> ") "].

Null 9:57:34 Therefore, unit generates the "(", <expression>, ")" subnodes.

Some questions: 9:57:43 Well

Nulshunde: 58: 18 Then, let's look at "(" this syntax tree node is exactly "(" this word type, so "(" It's done, and then we will process the word "19" later

Nulshunde: 58: 45 And so on

Nulshunde: 58: 48 You will understand.

Some questions: 9:58:58 So "(" is a leaf node?

Nulshunde: 59: 04 Pair

Nulshunde: 59: 34

Some questions: 10:01:43 That is to say, every leaf node that can't be processed will be stopped?

Null10: 01: 53 Pair

Some questions: 10:02:58 The child nodes of the root node are multiply and plusopt. What about plusopt?

Null10: 03: 01 "("This syntax tree node is a Terminator, so no child nodes are generated. The previous expressions, multiply, and so on are non-Terminators.

Some questions: 10:03:14 Well, I understand this.

Null10: 03: 30 I just processed "(", the expression below is

Null10: 03: 35 The newly generated expression

Null10: 04: 28 Then you will find that after the expression is processed, you should process ")".

Null10: 04: 46 ")"The Unit Terminator corresponds

Null10: 05: 55 Now that the unit node is processed, let's look at the syntax tree. The multiply node is processed, so we need to process the multiplyopt node.

Null10: 09: 27 MultiplyoptWhich candidate formula is corresponding to the "*" Word type in the ll1 analysis table?

Some questions: 10:11:55 It should be * <unit>

Null10: 12: 05 You learned

Null10: 12: 28 Therefore, multiplyopt generates two subnodes: "*" and unit.

Some questions: 10:13:29 But why search for multiplyopt and "*" instead of anything else ..

Null10: 14: 14 Because the preceding code has been processed (19 + 18) * (19-18) (19 + 18 ).

Some questions: 10:14:35 Well, I'll try again ~

Null10: 14: 43

Some questions: 10:15:25 Oh, that is to say, (19 + 18) These leaf nodes have already appeared, right?

Null10: 15: 29 Pair

Some questions: 10:15:57 Well, I understand ~ Do some exercises now ..

Null10: 16: 02 Fuel

Null10: 17: 47 Can I post the chat content to my blog? Easy for others to understand

Some questions: 10:18:20 Nhang ~ But can I just remove the nickname ..

Null10: 18: 28 No problem

Null10: 21: 31 Which blog did you read to ask me?

Some questions: 10:23:41 Http://www.cnblogs.com/bitzhuwei/archive/2013/06/05/CompilerDesignAndImp4Context-freeGrammar.html

Some questions: 10:23:45 This article ..

Null10: 24: 05 It seems that I wrote too poorly,

Some questions: 10:24:40 Should 4 in the ll1 analysis table (3/3) be included in plusopt and?

Null10: 25: 49 Oh, it seems like ah

Null10: 26: 29 Thank you for choosing the wrong one.

Some questions: 10:26:39 No ~ Thank you ~

If you have any questions or want code, you can leave a message on my blog http://bitzhuwei.cnblogs.com with my other contact information on it. Thank you for your harassment ~