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//! The main macro expander.
use crate::ast::{Expr, Spanned};
use crate::diagnostics::{Error, Result, Span};
use crate::eval::Environment;
use super::{
MacroTransformer, MacroEnvironment, HygieneContext, PatternBindings,
install_builtin_macros, next_hygiene_id, parse_syntax_rules, syntax_rules_to_macro_transformer
};
use std::collections::HashMap;
use std::rc::Rc;
/// The main macro expander.
#[derive(Debug, Clone)]
pub struct MacroExpander {
/// Environment containing macro definitions
macro_env: Rc<MacroEnvironment>,
/// Current expansion depth (for detecting infinite recursion)
expansion_depth: usize,
/// Maximum allowed expansion depth
max_expansion_depth: usize,
/// Current hygiene context
hygiene_context: HygieneContext,
}
// SAFETY: MacroExpander is designed to be used in a thread-safe context through
// external synchronization (Mutex). While it contains Rc and RefCell internally,
// these are only accessed through synchronized methods, ensuring thread safety.
// The macro expansion system is coordinated by the GC integration layer which
// ensures proper synchronization.
unsafe impl Send for MacroExpander {}
unsafe impl Sync for MacroExpander {}
impl MacroExpander {
/// Creates a new macro expander.
pub fn new() -> Self {
Self {
macro_env: Rc::new(MacroEnvironment::new()),
expansion_depth: 0,
max_expansion_depth: 100,
hygiene_context: HygieneContext::new(),
}
}
/// Ensures that the macro expander can access global syntax elements.
/// This is crucial for macros that expand to basic special forms like 'lambda', 'if', etc.
fn ensure_global_syntax_access(&mut self) {
// Currently, we rely on the global environment binding special forms as symbols
// This allows macro templates to reference them properly during expansion
// The actual binding happens in create_global_environment()
// where bind_special_forms_as_identifiers() is called
// For now, we just ensure the macro environment is properly initialized
// Future enhancement: could create a dedicated macro-time environment
// that has explicit mappings for special forms
}
/// Creates a new macro expander with built-in macros.
pub fn with_builtins() -> Self {
let mut expander = Self::new();
// Initialize macro environment with access to global environment
// This ensures macros can reference basic syntax like 'lambda', 'if', etc.
expander.ensure_global_syntax_access();
install_builtin_macros(&mut expander);
expander
}
/// Expands a single expression.
pub fn expand(&mut self, expr: &Spanned<Expr>) -> Result<Spanned<Expr>> {
self.expand_inner(expr, &mut Vec::new())
}
/// Expands all expressions in a program.
pub fn expand_program(&mut self, program: &crate::ast::Program) -> Result<crate::ast::Program> {
let mut expanded_expressions = Vec::new();
for expr in &program.expressions {
let expanded = self.expand(expr)?;
expanded_expressions.push(expanded);
}
Ok(crate::ast::Program::with_expressions(expanded_expressions))
}
/// Internal expansion method with recursion tracking.
fn expand_inner(
&mut self,
expr: &Spanned<Expr>,
expansion_trail: &mut Vec<String>,
) -> Result<Spanned<Expr>> {
// Check for infinite recursion
if self.expansion_depth >= self.max_expansion_depth {
return Err(Box::new(Error::macro_error(
"Macro expansion depth exceeded".to_string(),
expr.span,
)));
}
match &expr.inner {
Expr::Application { operator, operands } => {
// Check if the operator is a macro
if let Expr::Identifier(name) = &operator.inner {
if let Some(transformer) = self.macro_env.lookup(name) {
// Prevent infinite recursion
if expansion_trail.contains(name) {
return Err(Box::new(Error::macro_error(
format!("Recursive macro expansion detected: {name}"),
expr.span,
)));
}
expansion_trail.push(name.clone());
self.expansion_depth += 1;
let result = self.expand_macro(&transformer, operands, expr.span);
self.expansion_depth -= 1;
expansion_trail.pop();
// Recursively expand the result
match result {
Ok(expanded) => self.expand_inner(&expanded, expansion_trail),
Err(e) => Err(e),
}
} else {
// Not a macro, expand operands
self.expand_application(operator, operands, expr.span)
}
} else {
// Operator is not an identifier, expand normally
self.expand_application(operator, operands, expr.span)
}
}
// Special forms that contain expressions to expand
Expr::Lambda { formals, metadata, body } => {
let expanded_body = self.expand_body(body)?;
let expanded_metadata = self.expand_metadata(metadata)?;
Ok(Spanned::new(
Expr::Lambda {
formals: formals.clone(),
metadata: expanded_metadata,
body: expanded_body,
},
expr.span,
))
}
Expr::If { test, consequent, alternative } => {
let expanded_test = self.expand_inner(test, expansion_trail)?;
let expanded_consequent = self.expand_inner(consequent, expansion_trail)?;
let expanded_alternative = if let Some(alt) = alternative {
Some(Box::new(self.expand_inner(alt, expansion_trail)?))
} else {
None
};
Ok(Spanned::new(
Expr::If {
test: Box::new(expanded_test),
consequent: Box::new(expanded_consequent),
alternative: expanded_alternative,
},
expr.span,
))
}
Expr::Define { name, value, metadata } => {
let expanded_value = self.expand_inner(value, expansion_trail)?;
let expanded_metadata = self.expand_metadata(metadata)?;
Ok(Spanned::new(
Expr::Define {
name: name.clone(),
value: Box::new(expanded_value),
metadata: expanded_metadata,
},
expr.span,
))
}
Expr::DefineSyntax { name: _, transformer: _ } => {
// Define-syntax should not be expanded by the macro expander
// It should be handled directly by the evaluator
Ok(expr.clone())
}
Expr::SyntaxRules { literals, rules } => {
// syntax-rules should not appear at top level normally, but handle it
// Convert to macro transformer representation
let syntax_rules_transformer = super::parse_syntax_rules(expr, Rc::new(Environment::new(None, 0)))?;
let macro_transformer = super::syntax_rules_to_macro_transformer(syntax_rules_transformer);
// For demonstration, create a temporary identifier
let temp_name = format!("temp-syntax-{}", next_hygiene_id());
self.macro_env.define(temp_name, macro_transformer);
Ok(Spanned::new(Expr::Begin(vec![]), expr.span)) // Expand to empty begin
}
// Other expression types that don't need expansion
_ => Ok(expr.clone()),
}
}
/// Expands a macro application.
fn expand_macro(
&mut self,
transformer: &MacroTransformer,
operands: &[Spanned<Expr>],
span: Span,
) -> Result<Spanned<Expr>> {
// Create input expression for pattern matching
let input_expr = Spanned::new(
Expr::Application {
operator: Box::new(Spanned::new(
Expr::Identifier(transformer.name.clone().unwrap_or_else(|| "anonymous-macro".to_string())),
span,
)),
operands: operands.to_vec(),
},
span,
);
// Try to match the pattern against the input
let bindings = self.match_pattern(&transformer.pattern, &input_expr)?;
// Expand the template with the bindings
let expanded = self.expand_template(&transformer.template, &bindings, span)?;
// Apply hygiene transformations
self.apply_hygiene(expanded, &transformer.definition_env)
}
/// Expands a function application (non-macro).
fn expand_application(
&mut self,
operator: &Spanned<Expr>,
operands: &[Spanned<Expr>],
span: Span,
) -> Result<Spanned<Expr>> {
let expanded_operator = self.expand_inner(operator, &mut Vec::new())?;
let mut expanded_operands = Vec::new();
for operand in operands {
expanded_operands.push(self.expand_inner(operand, &mut Vec::new())?);
}
Ok(Spanned::new(
Expr::Application {
operator: Box::new(expanded_operator),
operands: expanded_operands,
},
span,
))
}
/// Expands a sequence of expressions.
fn expand_body(&mut self, body: &[Spanned<Expr>]) -> Result<Vec<Spanned<Expr>>> {
let mut expanded = Vec::new();
for expr in body {
expanded.push(self.expand_inner(expr, &mut Vec::new())?);
}
Ok(expanded)
}
/// Expands metadata expressions.
fn expand_metadata(
&mut self,
metadata: &HashMap<String, Spanned<Expr>>,
) -> Result<HashMap<String, Spanned<Expr>>> {
let mut expanded = HashMap::new();
for (key, value) in metadata {
expanded.insert(key.clone(), self.expand_inner(value, &mut Vec::new())?);
}
Ok(expanded)
}
/// Evaluates a macro transformer expression.
fn evaluate_transformer(&self, transformer_expr: &Spanned<Expr>, _expansion_trail: Vec<String>) -> Result<MacroTransformer> {
// Check if this is a syntax-rules form (as application)
if let Expr::Application { operator, .. } = &transformer_expr.inner {
if let Expr::Identifier(name) = &operator.inner {
if name == "syntax-rules" {
// Parse syntax-rules and convert to MacroTransformer
// For now, create a basic environment - this will be improved when
// macro/evaluator integration is complete
let empty_env = Rc::new(Environment::new(None, 0));
let syntax_rules = parse_syntax_rules(
transformer_expr,
empty_env,
)?;
return Ok(syntax_rules_to_macro_transformer(syntax_rules));
}
}
}
// Check if this is a direct SyntaxRules expression
if let Expr::SyntaxRules { literals, rules } = &transformer_expr.inner {
// Handle SyntaxRules directly without going through parse_syntax_rules
// Create the transformer directly from the parsed structure
let definition_env = Rc::new(Environment::new(None, 0));
// Convert the parsed rules to SyntaxRule structures
let mut syntax_rules = Vec::new();
for (pattern_expr, template_expr) in rules {
// Each rule is a (pattern, template) pair
let pattern = Self::expr_to_pattern(pattern_expr)?;
let template = Self::expr_to_template(template_expr)?;
syntax_rules.push(crate::macro_system::syntax_rules::SyntaxRule {
pattern,
template,
});
}
let transformer = crate::macro_system::SyntaxRulesTransformer {
literals: literals.clone(),
rules: syntax_rules,
name: None,
definition_env,
custom_ellipsis: None,
srfi_149_mode: true, // Enable SRFI-149 by default
};
return Ok(syntax_rules_to_macro_transformer(transformer));
}
Err(Box::new(Error::macro_error(
format!("Expected syntax-rules transformer, got {:?}", transformer_expr.inner),
transformer_expr.span,
)))
}
/// Converts an expression to a pattern.
fn expr_to_pattern(expr: &Spanned<Expr>) -> Result<crate::macro_system::Pattern> {
match &expr.inner {
Expr::Identifier(name) => Ok(crate::macro_system::Pattern::identifier(name)),
Expr::Application { operator, operands } => {
let op_pattern = Self::expr_to_pattern(operator)?;
let mut arg_patterns = Vec::new();
for arg in operands {
arg_patterns.push(Self::expr_to_pattern(arg)?);
}
let mut patterns = vec![op_pattern];
patterns.extend(arg_patterns);
Ok(crate::macro_system::Pattern::list(patterns))
}
Expr::Literal(lit) => Ok(crate::macro_system::Pattern::literal(lit.clone())),
_ => {
// Fallback to variable pattern
Ok(crate::macro_system::Pattern::variable("_"))
}
}
}
/// Converts an expression to a template.
fn expr_to_template(expr: &Spanned<Expr>) -> Result<crate::macro_system::Template> {
match &expr.inner {
Expr::Identifier(name) => Ok(crate::macro_system::Template::identifier(name)),
Expr::Application { operator, operands } => {
let op_template = Self::expr_to_template(operator)?;
let mut arg_templates = Vec::new();
for arg in operands {
arg_templates.push(Self::expr_to_template(arg)?);
}
let mut templates = vec![op_template];
templates.extend(arg_templates);
Ok(crate::macro_system::Template::list(templates))
}
Expr::Literal(lit) => Ok(crate::macro_system::Template::literal(lit.clone())),
_ => {
// Fallback to identifier template
Ok(crate::macro_system::Template::identifier("unknown"))
}
}
}
/// Matches a pattern against an expression.
fn match_pattern(
&self,
pattern: &super::Pattern,
expr: &Spanned<Expr>,
) -> Result<PatternBindings> {
pattern.match_expr(expr)
}
/// Expands a template with the given bindings.
fn expand_template(
&self,
template: &super::Template,
bindings: &PatternBindings,
span: Span,
) -> Result<Spanned<Expr>> {
template.expand(bindings, span)
}
/// Applies hygiene transformations to ensure lexical scoping.
fn apply_hygiene(
&mut self,
expr: Spanned<Expr>,
definition_env: &Environment,
) -> Result<Spanned<Expr>> {
self.hygiene_context.rename_identifiers(expr, definition_env)
}
/// Defines a new macro.
pub fn define_macro(&mut self, name: String, transformer: MacroTransformer) {
self.macro_env.define(name, transformer);
}
/// Defines a syntax-rules macro directly.
pub fn define_syntax_rules_macro(&mut self, name: String, syntax_rules: crate::macro_system::SyntaxRulesTransformer) {
let transformer = crate::macro_system::syntax_rules_to_macro_transformer(syntax_rules);
self.macro_env.define(name, transformer);
}
/// Gets the macro environment.
pub fn macro_env(&self) -> &MacroEnvironment {
&self.macro_env
}
}
impl Default for MacroExpander {
fn default() -> Self {
Self::with_builtins()
}
}