Editing Abstract syntax tree (section)

{{Short description|Tree representation of the abstract syntactic structure of source code}}
{{For|the trees used in linguistics|parse tree}}
{{no footnotes|date=February 2013}}
[[File:Abstract syntax tree for Euclidean algorithm.svg|thumb|400px|An abstract syntax tree for the following code for the [[Euclidean algorithm]]:<syntaxhighlight lang="python">
while b ≠ 0:
    if a > b:
        a := a - b
    else:
        b := b - a
return a
</syntaxhighlight>]]

An '''abstract syntax tree''' ('''AST''') is a data structure used in [[computer science]] to represent the structure of a program or code snippet. It is a [[Tree (data structure)|tree]] representation of the [[abstract syntax|abstract syntactic]] structure of text (often [[source code]]) written in a [[formal language]]. Each node of the tree denotes a construct occurring in the text. It is sometimes called just a '''syntax tree'''.

The syntax is "abstract" in the sense that it does not represent every detail appearing in the real syntax, but rather just the structural or content-related details. For instance, grouping [[Bracket#Parentheses|parentheses]] are implicit in the tree structure, so these do not have to be represented as separate nodes. Likewise, a syntactic construct like an if-condition-then statement may be denoted by means of a single node with three branches.

This distinguishes abstract syntax trees from concrete syntax trees, traditionally designated [[parse tree]]s. Parse trees are typically built by a [[parser]] during the source code translation and [[compiler|compiling]] process. Once built, additional information is added to the AST by means of subsequent processing, e.g., [[Semantic analysis (compilers)|contextual analysis]].

Abstract syntax trees are also used in [[program analysis]] and [[program transformation]] systems.