271 lines
8.2 KiB
Rust
271 lines
8.2 KiB
Rust
use std::collections::HashMap;
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use crate::{
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ast,
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errors::{ErrorKind, SloxError, SloxResult},
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tokens::Token,
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};
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/// Resolved variables. Pointers to the AST nodes using the variables are
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/// associated with the relative depth at which the variable definition will be
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/// found.
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pub type ResolvedVariables = HashMap<usize, usize>;
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/// Resolve all variables in a program's AST.
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pub fn resolve_variables(program: &ast::ProgramNode) -> SloxResult<ResolvedVariables> {
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let mut state = ResolverState::default();
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program.resolve(&mut state).map(|_| state.resolved)
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}
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type ResolverResult = SloxResult<()>;
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/// The state of the resolver.
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#[derive(Default)]
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struct ResolverState {
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/// The stack of scopes. Each scope maps variable names to a flag that
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/// indicates whether the variable has been defined or not.
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scopes: Vec<HashMap<String, bool>>,
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/// The result of the resolver pass.
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resolved: ResolvedVariables,
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}
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impl ResolverState {
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/// Enter a new scope.
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fn begin_scope(&mut self) {
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self.scopes.push(HashMap::new());
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}
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/// End the current scope.
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fn end_scope(&mut self) {
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self.scopes.pop();
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}
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/// Try to declare a variable. If the scope already contains a variable
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/// declaration for the same name, return an error.
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fn declare(&mut self, name: &Token) -> ResolverResult {
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if !self.scopes.is_empty() {
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let idx = self.scopes.len() - 1;
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let scope = &mut self.scopes[idx];
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if scope.contains_key(&name.lexeme as &str) {
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return Err(SloxError::with_token(
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ErrorKind::Parse,
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name,
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"already a variable with this name in this scope".to_owned(),
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));
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} else {
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scope.insert(name.lexeme.clone(), false);
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}
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}
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return Ok(());
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}
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/// Define a new variable.
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fn define(&mut self, name: &Token) {
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if !self.scopes.is_empty() {
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let idx = self.scopes.len() - 1;
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let top = &mut self.scopes[idx];
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top.insert(name.lexeme.clone(), true);
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}
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}
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/// Check for a variable in the current scope, if there is one.
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fn check(&self, name: &str) -> Option<bool> {
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if self.scopes.is_empty() {
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None
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} else {
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let idx = self.scopes.len() - 1;
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self.scopes[idx].get(name).cloned()
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}
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}
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/// Try to resolve some access to a variable. If a local variable is found
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/// matching the specified name, add it to the resolution map.
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fn resolve_local(&mut self, expr_id: &usize, name: &Token) {
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let mut i = self.scopes.len();
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while i != 0 {
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i -= 1;
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if self.scopes[i].contains_key(&name.lexeme as &str) {
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self.mark_resolved(expr_id, self.scopes.len() - 1 - i);
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return;
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}
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}
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}
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/// Add an entry to the resolution map for an AST node.
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fn mark_resolved(&mut self, expr_id: &usize, depth: usize) {
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self.resolved.insert(*expr_id, depth);
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}
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}
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/// Process a function declaration.
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fn resolve_function(
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rs: &mut ResolverState,
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params: &[Token],
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body: &Vec<ast::StmtNode>,
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) -> ResolverResult {
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rs.begin_scope();
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for param in params {
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rs.declare(param)?;
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rs.define(param);
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}
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// Unlike the original Lox, function arguments and function bodies do
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// not use the same environment.
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rs.begin_scope();
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let result = body.resolve(rs);
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rs.end_scope();
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rs.end_scope();
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result
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}
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/// Helper trait used to visit the various AST nodes with the resolver.
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trait VarResolver {
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/// Try to resolve local variables under some AST node.
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fn resolve(&self, rs: &mut ResolverState) -> ResolverResult;
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}
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impl VarResolver for ast::ProgramNode {
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fn resolve(&self, rs: &mut ResolverState) -> ResolverResult {
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self.0.resolve(rs)
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}
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}
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impl VarResolver for Vec<ast::StmtNode> {
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fn resolve(&self, rs: &mut ResolverState) -> ResolverResult {
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for stmt in self.iter() {
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stmt.resolve(rs)?;
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}
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Ok(())
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}
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}
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impl VarResolver for ast::StmtNode {
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fn resolve(&self, rs: &mut ResolverState) -> ResolverResult {
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match self {
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ast::StmtNode::Block(stmts) => {
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rs.begin_scope();
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let result = stmts.resolve(rs);
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rs.end_scope();
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result
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}
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ast::StmtNode::VarDecl(name, None) => {
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rs.declare(name)?;
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rs.define(name);
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Ok(())
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}
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ast::StmtNode::VarDecl(name, Some(init)) => {
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rs.declare(name)?;
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init.resolve(rs)?;
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rs.define(name);
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Ok(())
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}
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ast::StmtNode::FunDecl { name, params, body } => {
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rs.declare(name)?;
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rs.define(name);
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resolve_function(rs, params, body)
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}
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ast::StmtNode::If {
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condition,
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then_branch,
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else_branch: None,
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} => condition.resolve(rs).and_then(|_| then_branch.resolve(rs)),
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ast::StmtNode::If {
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condition,
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then_branch,
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else_branch: Some(else_branch),
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} => condition
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.resolve(rs)
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.and_then(|_| then_branch.resolve(rs))
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.and_then(|_| else_branch.resolve(rs)),
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ast::StmtNode::Loop {
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label: _,
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condition,
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body,
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after_body,
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} => condition
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.resolve(rs)
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.and_then(|_| {
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if let Some(stmt) = after_body {
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stmt.resolve(rs)
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} else {
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Ok(())
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}
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})
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.and_then(|_| body.resolve(rs)),
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ast::StmtNode::Return {
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token: _,
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value: None,
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} => Ok(()),
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ast::StmtNode::Return {
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token: _,
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value: Some(expr),
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} => expr.resolve(rs),
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ast::StmtNode::Expression(expr) => expr.resolve(rs),
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ast::StmtNode::Print(expr) => expr.resolve(rs),
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ast::StmtNode::LoopControl {
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is_break: _,
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loop_name: _,
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} => Ok(()),
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}
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}
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}
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impl VarResolver for ast::ExprNode {
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fn resolve(&self, rs: &mut ResolverState) -> ResolverResult {
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match self {
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ast::ExprNode::Variable { name, id } => {
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if rs.check(&name.lexeme) == Some(false) {
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Err(SloxError::with_token(
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ErrorKind::Parse,
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name,
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"can't read local variable in its own initializer".to_owned(),
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))
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} else {
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rs.resolve_local(id, name);
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Ok(())
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}
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}
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ast::ExprNode::Assignment { name, value, id } => {
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value.resolve(rs)?;
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rs.resolve_local(id, name);
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Ok(())
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}
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ast::ExprNode::Lambda { params, body } => resolve_function(rs, params, body),
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ast::ExprNode::Logical {
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left,
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operator: _,
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right,
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} => left.resolve(rs).and_then(|_| right.resolve(rs)),
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ast::ExprNode::Binary {
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left,
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operator: _,
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right,
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} => left.resolve(rs).and_then(|_| right.resolve(rs)),
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ast::ExprNode::Unary { operator: _, right } => right.resolve(rs),
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ast::ExprNode::Grouping { expression } => expression.resolve(rs),
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ast::ExprNode::Litteral { value: _ } => Ok(()),
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ast::ExprNode::Call {
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callee,
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right_paren: _,
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arguments,
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} => callee.resolve(rs).and_then(|_| arguments.resolve(rs)),
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}
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}
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}
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impl VarResolver for Vec<ast::ExprNode> {
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fn resolve(&self, rs: &mut ResolverState) -> ResolverResult {
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for expr in self.iter() {
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expr.resolve(rs)?;
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}
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Ok(())
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}
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}
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