asts

An abstract syntax tree (AST) is a tree representation of the syntactic structure of source code, used by compilers and interpreters to analyze and transform programs. An AST encodes the essential grammatical relationships while omitting irrelevant punctuation and formatting, capturing constructs such as expressions, statements, and declarations as nodes.

ASTs differ from concrete syntax trees, which map closely to the source code's exact text. In an AST, nodes are typed (for example, BinaryExpression, IfStatement, Identifier, Literal) and children denote operands, blocks, or subcomponents.

Construction and use: After lexical analysis and parsing, a parser builds the AST via rules of the language grammar. ASTs are fed to semantic analysis, type checking, optimization, and code generation. They also enable tooling such as linters, refactoring, and IDE features.

For the expression a + b * c, the AST has a root node '+' with a left child representing 'a' and a right subtree '*' with leaves 'b' and 'c'.

Traversal: ASTs are typically traversed using depth-first or visitors patterns to perform transformations or analyses.

Variants and related concepts: augmented ASTs attach type information or symbol table entries. Parse trees and ASTs are related; IRs in compilers may be built from or alongside ASTs. Concrete syntax trees may be transformed into ASTs.

Limitations and considerations: ASTs balance abstraction with expressiveness; overly coarse trees can lose details needed for certain analyses, while very detailed trees can be large. Different languages may use different node types or normalization.