解析树和AST有什么区别？ | 解析树和AST有什么区别

本文介绍了解析树和AST有什么区别？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

它们是由编译过程的不同阶段生成的吗？

解决方案

这是基于 pg。 23

或中

Are they generated by different phases of a compiling process? Or are they just different names for the same thing?

解决方案

This is based on the Expression Evaluator grammar by Terrence Parr.

The grammar for this example:

grammar Expr002;

options
{
    output=AST;
    ASTLabelType=CommonTree; // type of $stat.tree ref etc...
}

prog    :   ( stat )+ ;

stat    :   expr NEWLINE        -> expr
        |   ID '=' expr NEWLINE -> ^('=' ID expr)
        |   NEWLINE             ->
        ;

expr    :   multExpr (( '+'^ | '-'^ ) multExpr)*
        ;

multExpr
        :   atom ('*'^ atom)*
        ;

atom    :   INT
        |   ID
        |   '('! expr ')'!
        ;

ID      : ('a'..'z' | 'A'..'Z' )+ ;
INT     : '0'..'9'+ ;
NEWLINE : '\r'? '\n' ;
WS      : ( ' ' | '\t' )+ { skip(); } ;

Input

x=1
y=2
3*(x+y)

Parse Tree

The parse tree is a concrete representation of the input. The parse tree retains all of the information of the input. The empty boxes represent whitespace, i.e. end of line.

AST

The AST is an abstract representation of the input. Notice that parens are not present in the AST because the associations are derivable from the tree structure.

For a more through explanation see Compilers and Compiler Generators pg. 23
or Abstract Syntax Trees on pg. 21 in Syntax and Semantics of Programming Languages

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