AST Generation¶

Overview¶

After ANTLR parses the source file it produces a Parse Tree whose nodes are ANTLR Context objects. ASTGenerationSTVisitor traverses this Parse Tree and converts it into a typed Abstract Syntax Tree (AST) built from the static inner classes defined in AST.java.

AST Node Hierarchy¶

All nodes extend the abstract Node interface. Each concrete node carries the children and data that are relevant for later phases:

Node	Description
`ProgLetInNode`	Top-level `let … in` program
`ProgNode`	Top-level expression-only program
`ClassNode`	Class declaration (fields + methods)
`FieldNode`	A class field (like a parameter)
`MethodNode`	A class method (like a function)
`FunNode`	Function declaration
`ParNode`	Function parameter
`VarNode`	Variable declaration
`IdNode`	Identifier use
`CallNode`	Function call
`ClassCallNode`	Method call (`obj.method(...)`)
`NewNode`	Object instantiation (`new C(...)`)
`EmptyNode`	`null` literal
`PlusNode` / `MinusNode`	Addition / subtraction
`TimesNode` / `DivNode`	Multiplication / division
`EqualNode` / `GreaterEqualNode` / `LessEqualNode`	Comparison
`AndNode` / `OrNode` / `NotNode`	Logical operators
`IfNode`	`if / then / else`
`PrintNode`	`print(exp)`
`IntNode`	Integer literal
`BoolNode`	Boolean literal

Type Nodes¶

Type information is represented separately as TypeNode subtypes that appear in symbol-table entries:

Type Node	Meaning
`IntTypeNode`	`int`
`BoolTypeNode`	`bool`
`RefTypeNode`	Reference to a class
`EmptyTypeNode`	Type of `null`
`ArrowTypeNode`	Function type (only in STentry)
`MethodTypeNode`	Method type (only in STentry)
`ClassTypeNode`	Class type (maps field/method indices to types)

Accept–Visit Cycle¶

The visitor pattern uses a two-step dispatch:

The visitor calls visit(node) → delegates to node.accept(this).
The node calls visitor.visitNode(this) passing its specific type.

This double dispatch allows the visitor to select the correct visitNode overload at runtime without explicit casts.