Make a Lisp
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/*
* Copyright (C) 2023 Riyyi
*
* SPDX-License-Identifier: MIT
*/
#include <iterator> // sd::advance, std::next, std::prev
#include <list>
#include <memory> // std::static_pointer_cast
#include <span> // std::span
#include <string>
#include "ast.h"
#include "environment.h"
#include "error.h"
#include "eval.h"
#include "forward.h"
#include "types.h"
namespace blaze {
Eval::Eval(ASTNodePtr ast, EnvironmentPtr env)
: m_ast(ast)
, m_env(env)
{
}
// -----------------------------------------
void Eval::eval()
{
m_ast_stack = std::stack<ASTNodePtr>();
m_env_stack = std::stack<EnvironmentPtr>();
m_ast_stack.push(m_ast);
m_env_stack.push(m_env);
m_ast = evalImpl();
}
ASTNodePtr Eval::evalImpl()
{
ASTNodePtr ast = nullptr;
EnvironmentPtr env = nullptr;
while (true) {
if (m_ast_stack.size() == 0) {
return nullptr;
}
if (m_env_stack.size() == 0) {
m_env_stack.push(m_env);
}
ast = m_ast_stack.top();
env = m_env_stack.top();
m_ast_stack.pop();
m_env_stack.pop();
if (!is<List>(ast.get())) {
return evalAst(ast, env);
}
auto list = std::static_pointer_cast<List>(ast);
if (list->empty()) {
return ast;
}
// Special forms
auto nodes = list->nodes();
if (is<Symbol>(nodes.front().get())) {
auto symbol = std::static_pointer_cast<Symbol>(nodes.front())->symbol();
nodes.pop_front();
if (symbol == "def!") {
return evalDef(nodes, env);
}
if (symbol == "let*") {
evalLet(nodes, env);
continue; // TCO
}
if (symbol == "do") {
evalDo(nodes, env);
continue; // TCO
}
if (symbol == "if") {
evalIf(nodes, env);
continue; // TCO
}
if (symbol == "fn*") {
return evalFn(nodes, env);
}
}
auto evaluated_list = std::static_pointer_cast<List>(evalAst(ast, env));
if (evaluated_list == nullptr) {
return nullptr;
}
// Regular list
if (is<Lambda>(evaluated_list->nodes().front().get())) {
auto evaluated_nodes = evaluated_list->nodes();
// car
auto lambda = std::static_pointer_cast<Lambda>(evaluated_nodes.front());
// cdr
evaluated_nodes.pop_front();
m_ast_stack.push(lambda->body());
m_env_stack.push(Environment::create(lambda, evaluated_nodes));
continue; // TCO
}
// Function call
return apply(evaluated_list);
}
}
ASTNodePtr Eval::evalAst(ASTNodePtr ast, EnvironmentPtr env)
{
if (ast == nullptr || env == nullptr) {
return nullptr;
}
ASTNode* ast_raw_ptr = ast.get();
if (is<Symbol>(ast_raw_ptr)) {
auto result = env->get(std::static_pointer_cast<Symbol>(ast)->symbol());
if (!result) {
Error::the().add(format("'{}' not found", ast));
return nullptr;
}
return result;
}
else if (is<Collection>(ast_raw_ptr)) {
std::shared_ptr<Collection> result = nullptr;
(is<List>(ast_raw_ptr)) ? result = makePtr<List>() : result = makePtr<Vector>();
auto nodes = std::static_pointer_cast<Collection>(ast)->nodes();
for (auto node : nodes) {
m_ast_stack.push(node);
m_env_stack.push(env);
ASTNodePtr eval_node = evalImpl();
if (eval_node == nullptr) {
return nullptr;
}
result->add(eval_node);
}
return result;
}
else if (is<HashMap>(ast_raw_ptr)) {
auto result = makePtr<HashMap>();
auto elements = std::static_pointer_cast<HashMap>(ast)->elements();
for (auto& element : elements) {
m_ast_stack.push(element.second);
m_env_stack.push(env);
ASTNodePtr element_node = evalImpl();
if (element_node == nullptr) {
return nullptr;
}
result->addElement(element.first, element_node);
}
return result;
}
return ast;
}
ASTNodePtr Eval::evalDef(const std::list<ASTNodePtr>& nodes, EnvironmentPtr env)
{
if (nodes.size() != 2) {
Error::the().add(format("wrong number of arguments: def!, {}", nodes.size()));
return nullptr;
}
auto first_argument = *nodes.begin();
auto second_argument = *std::next(nodes.begin());
// First element needs to be a Symbol
if (!is<Symbol>(first_argument.get())) {
Error::the().add(format("wrong argument type: symbol, {}", first_argument));
return nullptr;
}
std::string symbol = std::static_pointer_cast<Symbol>(first_argument)->symbol();
m_ast_stack.push(second_argument);
m_env_stack.push(env);
ASTNodePtr value = evalImpl();
// Dont overwrite symbols after an error
if (Error::the().hasAnyError()) {
return nullptr;
}
// Modify existing environment
return env->set(symbol, value);
}
void Eval::evalLet(const std::list<ASTNodePtr>& nodes, EnvironmentPtr env)
{
if (nodes.size() != 2) {
Error::the().add(format("wrong number of arguments: let*, {}", nodes.size()));
return;
}
auto first_argument = *nodes.begin();
auto second_argument = *std::next(nodes.begin());
// First argument needs to be a List or Vector
if (!is<Collection>(first_argument.get())) {
Error::the().add(format("wrong argument type: collection, '{}'", first_argument));
return;
}
// Get the nodes out of the List or Vector
std::list<ASTNodePtr> binding_nodes;
auto bindings = std::static_pointer_cast<Collection>(first_argument);
binding_nodes = bindings->nodes();
// List or Vector needs to have an even number of elements
size_t count = binding_nodes.size();
if (count % 2 != 0) {
Error::the().add(format("wrong number of arguments: {}, {}", "let* bindings", count));
return;
}
// Create new environment
auto let_env = Environment::create(env);
for (auto it = binding_nodes.begin(); it != binding_nodes.end(); std::advance(it, 2)) {
// First element needs to be a Symbol
if (!is<Symbol>(*it->get())) {
Error::the().add(format("wrong argument type: symbol, '{}'", *it));
return;
}
std::string key = std::static_pointer_cast<Symbol>(*it)->symbol();
m_ast_stack.push(*std::next(it));
m_env_stack.push(let_env);
ASTNodePtr value = evalImpl();
let_env->set(key, value);
}
// TODO: Remove limitation of 3 arguments
// Eval all values in this new env, return last sexp of the result
m_ast_stack.push(second_argument);
m_env_stack.push(let_env);
return; // TCO
}
void Eval::evalDo(const std::list<ASTNodePtr>& nodes, EnvironmentPtr env)
{
if (nodes.size() == 0) {
Error::the().add(format("wrong number of arguments: do, {}", nodes.size()));
return;
}
// Evaluate all nodes except the last
for (auto it = nodes.begin(); it != std::prev(nodes.end(), 1); ++it) {
m_ast_stack.push(*it);
m_env_stack.push(env);
evalImpl();
}
// Eval last node
m_ast_stack.push(nodes.back());
m_env_stack.push(env);
return; // TCO
}
void Eval::evalIf(const std::list<ASTNodePtr>& nodes, EnvironmentPtr env)
{
if (nodes.size() != 2 && nodes.size() != 3) {
Error::the().add(format("wrong number of arguments: if, {}", nodes.size()));
return;
}
auto first_argument = *nodes.begin();
auto second_argument = *std::next(nodes.begin());
auto third_argument = (nodes.size() == 3) ? *std::next(std::next(nodes.begin())) : makePtr<Value>(Value::Nil);
m_ast_stack.push(first_argument);
m_env_stack.push(env);
auto first_evaluated = evalImpl();
if (!is<Value>(first_evaluated.get())
|| std::static_pointer_cast<Value>(first_evaluated)->state() == Value::True) {
m_ast_stack.push(second_argument);
m_env_stack.push(env);
return; // TCO
}
m_ast_stack.push(third_argument);
m_env_stack.push(env);
return; // TCO
}
#define ARG_COUNT_CHECK(name, comparison, size) \
if (comparison) { \
Error::the().add(format("wrong number of arguments: {}, {}", name, size)); \
return nullptr; \
}
#define AST_CHECK(type, value) \
if (!is<type>(value.get())) { \
Error::the().add(format("wrong argument type: {}, {}", #type, value)); \
return nullptr; \
}
#define AST_CAST(type, value, variable) \
AST_CHECK(type, value) \
auto variable = std::static_pointer_cast<type>(value);
ASTNodePtr Eval::evalFn(const std::list<ASTNodePtr>& nodes, EnvironmentPtr env)
{
ARG_COUNT_CHECK("fn*", nodes.size() != 2, nodes.size());
auto first_argument = *nodes.begin();
auto second_argument = *std::next(nodes.begin());
// First element needs to be a List or Vector
AST_CAST(Collection, first_argument, collection);
std::vector<std::string> bindings;
for (auto node : collection->nodes()) {
// All nodes need to be a Symbol
AST_CAST(Symbol, node, symbol);
bindings.push_back(symbol->symbol());
}
return makePtr<Lambda>(bindings, second_argument, env);
}
ASTNodePtr Eval::apply(std::shared_ptr<List> evaluated_list)
{
if (evaluated_list == nullptr) {
return nullptr;
}
auto nodes = evaluated_list->nodes();
if (!is<Function>(nodes.front().get())) {
Error::the().add(format("invalid function: {}", nodes.front()));
return nullptr;
}
// car
auto function = std::static_pointer_cast<Function>(nodes.front())->function();
// cdr
nodes.pop_front();
return function(nodes);
}
} // namespace blaze