lisp-compiler/parser.cpp

/**
 * lisp-compiler: Compiles LISP using LLVM.
 * Copyright (C) 2022  Clyne Sullivan
 *
 * This program is free software: you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * @file parser.cpp
 * @brief Source code parser to produce AST.
 */

#include "parser.hpp"

#include <algorithm>
#include <cctype>
#include <cstdlib>
#include <vector>

void Parser::addString(const std::string& str)
{
    if (!str.empty())
        std::copy(str.cbegin(), str.cend(), std::back_inserter(text));
}

void Parser::consumeWhitespace() noexcept
{
    while (isspace(text.front()))
        text.pop_front();
}

std::optional<std::string> Parser::consumeIdentifier() noexcept
{
    std::string ret;

    // TODO Accept all valid identifiers according to R7RS-small.
    if (isalpha(text.front())) {
        do {
            ret += text.front();
            text.pop_front();
        } while (isalnum(text.front()) || text.front() == '!');
    }

    if (ret.empty())
        return {};
    else
        return ret;
}

std::optional<std::variant<int, double>> Parser::consumeLiteralNumber()
{
    std::string ret;

    while (isdigit(text.front()) || text.front() == '.') {
        ret += text.front();
        text.pop_front();
    }

    if (ret.empty())
        return {};

    if (ret.find('.') == std::string::npos) {
        int r = strtol(ret.c_str(), nullptr, 0);
        // TODO Error check
        return r;
    } else {
        auto r = strtod(ret.c_str(), nullptr);
        // TODO Error check
        return r;
    }
}

std::deque<AST::Node *> Parser::parse()
{
    std::deque<AST::Node *> ret;

    errors.clear();
    while (!text.empty()) {
        consumeWhitespace();

        // At the top-level, there will only be procedure calls.
        auto node = parseProcedureCall();
        if (errors.empty() && node) {
            ret.push_back(node);
        } else {
           return {};
        }
    }

    return ret;
}

AST::Node *Parser::parseExpression()
{
    if (text.front() == '(') {
        return parseProcedureCall();
    } else if (auto id = consumeIdentifier(); id) {
        auto ident = new AST::Identifier;
        ident->name = *id;
        return ident;
    } else if (auto d = consumeLiteralNumber(); d) {
        auto lit = new AST::Literal;
        lit->type = AST::Literal::Number;
        lit->value = *d;
        return lit;
    }

    errors.push_back(InvalidExpression);
    return nullptr;
}

AST::Node *Parser::parseProcedureCall()
{
    // Consume the opening parenthesis.
    if (text.front() != '(') {
        errors.push_back(ExpectedProcedureCallOpen);
        return nullptr;
    } else {
        text.pop_front();
    }

    // Consume the identifier string.
    auto ident = parseExpression();
    if (ident == nullptr)
        return nullptr;

    // Check for special procedure calls.
    if (auto id = dynamic_cast<AST::Identifier *>(ident); id) {
        if (id->name == "lambda")
            return parseLambdaExpression();
        else if (id->name == "define")
            return parseDefinition();
        else if (id->name == "if")
            return parseConditional();
        else if (id->name == "set!")
            return parseAssignment();
    }

    // This is a regular procedure call.
    // Build the argument list:

    std::vector<AST::Node *> args;

    consumeWhitespace();
    while (text.front() != ')') {
        auto node = parseExpression();
        if (node == nullptr) {
            errors.push_back(InvalidOperand);
            return nullptr;
        }

        args.push_back(node);
        consumeWhitespace();
    }

    if (text.front() == ')') {
        text.pop_front();

        auto pc = new AST::ProcedureCall;
        pc->callee = ident;
        pc->operands = args;

        return pc;
    } else {
        errors.push_back(ExpectedProcedureCallClose);
        return nullptr;
    }
}

AST::Node *Parser::parseConditional()
{
    consumeWhitespace();
    auto cond = parseExpression();
    if (cond == nullptr) {
        errors.push_back(InvalidCondition);
        return nullptr;
    }

    consumeWhitespace();
    auto ift = parseExpression();
    if (ift == nullptr) {
        errors.push_back(InvalidThenBranch);
        return nullptr;
    }

    consumeWhitespace();
    auto iff = parseExpression();
    if (iff == nullptr) {
        errors.push_back(InvalidThenBranch);
        return nullptr;
    }

    consumeWhitespace();
    if (text.front() == ')') {
        text.pop_front();

        auto node = new AST::Conditional;
        node->cond = cond;
        node->iftrue = ift;
        node->iffalse = iff;
        return node;
    } else {
        errors.push_back(ExpectedProcedureCallClose);
        return nullptr;
    }
}

AST::Node *Parser::parseDefinition()
{
    consumeWhitespace();
    auto ident = consumeIdentifier();

    if (ident) {
        consumeWhitespace();

        auto val = parseExpression();
        if (val) {
            consumeWhitespace();
            if (text.front() == ')') {
                text.pop_front();

                auto id = new AST::Identifier;
                id->name = *ident;

                auto def = new AST::Definition;
                def->ident = id;
                def->value = val;
                return def;
            } else {
                errors.push_back(ExpectedProcedureCallClose);
            }
        } else {
            errors.push_back(InvalidInitializer);
        }
    } else {
        errors.push_back(ExpectedIdentifier);
    }

    return nullptr;
}

AST::Node *Parser::parseAssignment()
{
    consumeWhitespace();
    auto ident = consumeIdentifier();

    if (ident) {
        consumeWhitespace();

        auto val = parseExpression();
        if (val) {
            consumeWhitespace();
            if (text.front() == ')') {
                text.pop_front();

                auto id = new AST::Identifier;
                id->name = *ident;

                auto def = new AST::Assignment;
                def->ident = id;
                def->value = val;
                return def;
            } else {
                errors.push_back(ExpectedProcedureCallClose);
            }
        } else {
            errors.push_back(InvalidAssignValue);
        }
    } else {
        errors.push_back(ExpectedIdentifier);
    }

    return nullptr;
}

AST::Node *Parser::parseLambdaExpression()
{
    // Consume beginning of argument list.
    consumeWhitespace();
    if (text.front() != '(') {
        errors.push_back(ExpectedArgumentList);
        return nullptr;
    } else {
        text.pop_front();
    }

    // Consume argument list:

    std::vector<AST::Identifier *> args;

    while (text.front() != ')') {
        auto arg = consumeIdentifier();
        if (arg) {
            auto ident = new AST::Identifier;
            ident->name = *arg;
            args.push_back(ident);
        } else {
            errors.push_back(InvalidArgumentName);
            return nullptr;
        }

        consumeWhitespace();
    }

    // Consume arg list closing ')' that must be there.
    text.pop_front();

    // Consume lambda body:

    std::vector<AST::Node *> body;

    consumeWhitespace();
    while (text.front() != ')') {
        auto exp = parseExpression();

        if (!errors.empty()) {
            errors.push_back(InvalidLambdaBody);
            return nullptr;
        }

        body.push_back(exp);
        consumeWhitespace();
    }

    if (text.front() == ')') {
        text.pop_front();

        auto le = new AST::LambdaExpression;
        le->operands = args;
        le->body = body;

        return le;
    } else {
        errors.push_back(ExpectedProcedureCallClose);
        return nullptr;
    }
}

std::string Parser::describeErrors() noexcept
{
    std::string ret;

    for (auto& err : errors) {
        switch (err) {
        case ExpectedProcedureCallOpen:
            ret += "Expected opening \'(\' for procedure call.\n";
            break;
        case ExpectedIdentifier:
            ret += "Expected a valid identifier.\n";
            break;
        case ExpectedProcedureCallClose:
            ret += "Expected closing \')\' for procedure call.\n";
            break;
        case ExpectedArgumentList:
            ret += "Expected beginning of argument list.\n";
            break;
        case UnknownIdentifier:
            ret += "Given identifier is not valid.\n";
            break;
        case InvalidExpression:
            ret += "Expected a valid expression.\n";
            break;
        case InvalidOperand:
            ret += "Given invalid argument or operand.\n";
            break;
        case InvalidCondition:
            ret += "Given invalid condition for conditional statement.\n";
            break;
        case InvalidThenBranch:
            ret += "Given invalid \"then\" branch for conditional statement.\n";
            break;
        case InvalidElseBranch:
            ret += "Given invalid \"else\" branch for conditional statement.\n";
            break;
        case InvalidInitializer:
            ret += "Given invalid initializer for a declaration.\n";
            break;
        case InvalidAssignValue:
            ret += "Given invalid value for an assignment.\n";
            break;
        case InvalidArgumentName:
            ret += "Given invalid name for an argument.\n";
            break;
        case InvalidLambdaBody:
            ret += "Lambda body is invalid.\n";
            break;
        default:
            break;
        }
    }

    return ret;
}