rust-crafting-interpreters-part-1/src/ast.rs

use crate::tokens::Token;

/* --------- *
 * AST nodes *
 * --------- */

/// The AST node for the program
#[derive(Default, Debug, Clone)]
pub struct ProgramNode(pub Vec<StmtNode>);

/// An AST node that represents a statement.
#[derive(Debug, Clone)]
pub enum StmtNode {
    /// An single expression
    Expression(ExprNode),
    /// The print statement
    Print(ExprNode),
}

/// An AST node that represents an expression.
#[derive(Debug, Clone)]
pub enum ExprNode {
    /// Binary expression.
    Binary {
        left: Box<ExprNode>,
        operator: Token,
        right: Box<ExprNode>,
    },

    /// Unary expression.
    Unary {
        operator: Token,
        right: Box<ExprNode>,
    },

    /// Grouping expression, containing a sub-expression.
    Grouping { expression: Box<ExprNode> },

    /// A litteral value, represented by the corresponding token.
    Litteral { value: Token },
}

/* -------------------------------- *
 * Dumper trait and implementations *
 * -------------------------------- */

/// This trait should be implemented by nodes to allow AST dumps.
pub trait AstDumper {
    /// Dump the node as a string.
    fn dump(&self) -> String;
}

impl AstDumper for ProgramNode {
    fn dump(&self) -> String {
        self.0
            .iter()
            .map(|node| node.dump())
            .collect::<Vec<String>>()
            .join(" ")
    }
}

impl AstDumper for StmtNode {
    fn dump(&self) -> String {
        match self {
            Self::Expression(expr) => format!("( {} )", expr.dump()),
            Self::Print(expr) => format!("(print {})", expr.dump()),
        }
    }
}

impl AstDumper for ExprNode {
    fn dump(&self) -> String {
        match self {
            Self::Binary {
                left,
                operator,
                right,
            } => {
                format!("( {} {} {} )", operator.lexeme, left.dump(), right.dump())
            }
            Self::Unary { operator, right } => {
                format!("( {} {} )", operator.lexeme, right.dump())
            }
            Self::Grouping { expression } => {
                format!("( {} )", expression.dump())
            }
            Self::Litteral { value } => {
                if value.is_litteral() {
                    value.lexeme.clone()
                } else {
                    panic!("Unexpected token type for token {:#?}", value)
                }
            }
        }
    }
}