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. Here's an explanation of parse trees concrete syntax trees, CSTs and abstract syntax trees ASTs , in the context of compiler construction.
They're similar data structures, but they're constructed differently and used for different tasks. Parse trees are usually generated as the next step after lexical analysis which turns the source code into a series of tokens that can be viewed as meaningful units, as opposed to just a sequence of characters.
They are tree-like data structures that shows how an input string of terminals source code tokens has been generated by the grammar of the language in question. The root of the parse tree is the most general symbol of the grammar - the start symbol for example, statement , and the interior nodes represent nonterminal symbols that the start symbol expands to can include the start symbol itself , such as expression , statement , term , function call.
While parsing the compiler also performs various checks to ensure the correctness of syntax - and and syntax error reports can be imbedded into parser code. They can be used for syntax-directed translation via syntax-directed definitions or translation schemes, for simple tasks such as converting an infix expression to a postfix one. ASTs represent the syntactic structure of the some code. The trees of programming constructs such as expressions, flow control statements, etc - grouped into operators interior nodes and operands leaves.
The difference here is that nonterminals and terminals don't play a role, as ASTs don't deal with grammars and string generation, but programming constructs, and thus they represent relationships between such constructs, and not the ways they are generated by a grammar. For example, you could have a syntax tree such as for [ expr, expr, expr, stmnt ] represented inline , where for is an operator , and the elements inside the square brackets are its children representing C's for syntax - also composed out of operators etc.
ASTs are usually generated by compilers in the syntax analysis parsing phase as well, and are used later for semantic analysis, intermediate representation, code generation, etc.
From what I understand, the AST focuses more on the abstract relationships between the components of source code, while the parse tree focuses on the actual implementation of the grammar utilized by the language, including the nitpicky details.
They are definitely not the same, since another term for "parse tree" is "concrete syntax tree". I found this page which attempts to resolve this exact question. The AST only contains all 'useful' elements that will be used for further processing, while the parse tree contains all the artifacts spaces, brackets, An AST describes the source code conceptually, it doesn't need to contain all the syntactical elements required to parse some source code curly braces, keywords, parenthesis etc.
For a C-like language the Parse Tree would need to contain nodes for the 'if' keyword, parenthesis, curly braces also. Parse trees concretely reflect the syntax of the input language, making them distinct from the abstract syntax trees used in computer programming. A parse tree is a record of the rules and tokens used to match some input text whereas a syntax tree records the structure of the input and is insensitive to the grammar that produced it.
An Abstract Syntax Tree describes the parse tree logically. It does not need to contain all the syntactical constructs required to parse some source code white spaces, braces, keywords, parenthesis etc. Syntax tree is the compact form of a parse tree. Each interior node represents a grammar rule. They do not provide every characteristic information from the real syntax.
For example- no rule nodes, no parenthesis etc. Steps Involved Start pushing the symbols of the postfix expression into the stack one by one. When an operand is encountered, Push it into the stack. When an operator is encountered Push it into the stack.
A syntax tree, on the other hand, is a tree representation of the abstract syntactic structure of source code written in a programming language. Thus, this is the main difference between parse tree and syntax tree. Parsing tree, derivation tree, and concrete syntax tree are some other names for parse tree while abstract syntax tree is another name for the syntax tree.
Moreover, parse tree contains records of the rules tokens to match input texts while syntax tree contains records of the syntax of programming language. Hence, this is another major difference between parse tree and syntax tree.
The main difference between parse tree and syntax tree is that parse tree is a hierarchical structure that represents the derivation of the grammar to obtain input strings while syntax tree is a way of representing the syntax of a programming language as a hierarchical tree similar structure. She is passionate about sharing her knowldge in the areas of programming, data science, and computer systems. View all posts. Leave a Reply Cancel reply.
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