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In this article Xiaobian for you to introduce in detail "what are the knowledge points of the web interpreter mode", the content is detailed, the steps are clear, and the details are handled properly. I hope this article "what are the knowledge points of the web interpreter mode" can help you solve your doubts.

Grammatical modeling

As standard practice for interpreter patterns, the step after defining the syntax of a language is to prepare a class for each language element. For the examples of four operations, the class structure is as follows:

The class diagram is a little larger, so let's take a few rules as an example.

1. Generalization relation

Example: [5] PrimaryExpr::=NumericLiteral | ParenthesizedExpr | FunctionCall

The meaning of formula [5] is that the basic expression PrimaryExpr can be a numeric literal value NumerLiteral, a parenthesized expression ParemthesizedExpr, or a function call. Transforming into a class relationship is a generalization relationship. All places where PrimaryExpr applies can be replaced by one of NumericLiteral, ParenthesizedExpr, or FunctionCall.

two。 Combinatorial relationship

[2] AdditiveExpr::=MultiplicativeExpr ("+" >

When AdditiveExpr is composed of multiple MultiplicativeExpr, the relationship between them can be regarded as a combinatorial relationship.

When there is only one MultiplicativeExpr, the equation [2] can be reduced to:

AdditiveExpr::=MultiplicativeExpr

In this case, it can be regarded as a simple generalization relationship between the two.

3. Simple combinatorial relation

[7] ParenthesizedExpr::= "(" Expr ")"

Formula [7] can be regarded as a simple combinatorial relationship of 1 to 1.

Form a syntax tree

Look back at the expressions in the previous article:

100.0 * sin (29 + (23 * 6)) + sqrt (cos (34 * 5))

This expression is converted into a syntax tree as follows:

The analysis process is carried out from the top down along the class diagram until the appropriate type is found. For example, the initial analysis starts with AdditiveExpr, whose subordinate nodes should be multiple MultiplicativeExpr, but the right side does not meet the conditions of MultiplicativeExpr, so search down the class diagram until a qualified FuncitonCall is found. In this way, you can get the whole syntax tree over and over again.

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