metaforce/hecl/lib/Frontend/Parser.cpp

#include "hecl/hecl.hpp"
#include "hecl/Frontend.hpp"

/* Syntatical token parsing system */

namespace hecl::Frontend
{

/*
 * hecl   = { lf } call { lf { lf } call } { lf } .
 * call   = ident "(" [ expr { "," expr } ] ")" .
 * expr   = sum { ("+" | "-") sum } .
 * sum    = factor { ("*" | "/") factor } .
 * factor = value | "(" expr ")" .
 * value  = ( call [ "." ident ] )
 *        | [ "-" ] number
 *        .
*/

std::string IRNode::rep(int n, std::string_view s)
{
    std::string buf;
    buf.reserve(n * s.size());
    for (int i = 0; i < n; i++)
        buf.append(s);
    return buf;
}

std::string IRNode::fmt(int level) const
{
    std::string buf;
    auto indent = rep(level, "\t"sv);
    switch (kind)
    {
    case Kind::Call:
        buf.append(indent);
        buf.append("Call "sv).append(str);
        if (!children.empty())
        {
            buf.append(" {\n"sv);
            for (const IRNode& n : children)
            {
                buf.append(n.fmt(level + 1));
                buf.append("\n"sv);
            }
            buf.append(indent);
            buf.append("}"sv);
        }
        break;
    case Kind::Imm:
        buf.append(indent);
        buf.append("Imm "sv).append(hecl::Format("%f", val));
        break;
    case Kind::Binop:
        buf.append(indent);
        buf.append("Binop "sv).append(OpToStr(op)).append(" {\n"sv);
        buf.append(left->fmt(level + 1)).append("\n"sv);
        buf.append(right->fmt(level + 1)).append("\n"sv);
        buf.append(indent).append("}"sv);
        break;
    case Kind::Swizzle:
        buf.append(indent);
        buf.append("Swizzle \""sv).append(str);
        buf.append("\" {\n"sv);
        buf.append(left->fmt(level + 1)).append("\n"sv);
        buf.append(indent).append("}"sv);
        break;
    default:
        break;
    }
    return buf;
}


std::string IRNode::describe() const
{
    std::vector<std::string> l;
    l.push_back("kind="s + KindToStr(kind).data());
    if (!str.empty())
        l.push_back("str="s + str);
    if (kind == Kind::Binop)
    {
        l.push_back("op="s + OpToStr(op).data());
        l.push_back("left="s + left->toString());
        l.push_back("right="s + right->toString());
    }
    if (kind == Kind::Swizzle)
        l.push_back("node="s + left->toString());
    if (kind == Kind::Call)
    {
        std::string str = "children=["s;
        for (auto it = children.begin(); it != children.end(); ++it)
        {
            str += it->toString();
            if (&*it != &children.back())
                str += ';';
        }
        str += ']';
        l.push_back(str);
    }

    std::string str = "IRNode["s;
    for (auto it = l.begin(); it != l.end(); ++it)
    {
        str += *it;
        if (&*it != &l.back())
            str += ';';
    }
    str += ']';
    return str;
}

void Parser::check(Token::Kind expected)
{
    if (sym == expected)
        scan();
    else
        error("expected %s, was %s", Token::KindToStr(expected).data(), Token::KindToStr(sym).data());
}

IRNode Parser::call()
{
    check(Token::Kind::Ident);
    std::string name = t.str;

    std::list<IRNode> args;
    check(Token::Kind::Lpar);
    if (sym == Token::Kind::Lpar || sym == Token::Kind::Ident ||
        sym == Token::Kind::Number || sym == Token::Kind::Minus)
    {
        args.push_back(expr());

        while (sym == Token::Kind::Comma)
        {
            scan();
            args.push_back(expr());
        }
    }

    if (sym != Token::Kind::Rpar)
        error("expected expr|rpar, was %s", Token::KindToStr(sym).data());
    else
        scan();
    return IRNode(IRNode::Kind::Call, std::move(name), std::move(args), t.loc);
}

bool Parser::imm(const IRNode& a, const IRNode& b)
{
    return a.kind == IRNode::Kind::Imm && b.kind == IRNode::Kind::Imm;
}

IRNode Parser::expr()
{
    IRNode node = sum();
    while (sym == Token::Kind::Plus || sym == Token::Kind::Minus)
    {
        scan();
        Token::Kind op = t.kind;
        IRNode right = sum();
        switch (op)
        {
        case Token::Kind::Plus:
            if (imm(node, right)) // constant folding
                return IRNode(IRNode::Kind::Imm, node.val + right.val, t.loc);
            else
                node = IRNode(IRNode::Op::Add, std::move(node), std::move(right), t.loc);
            break;
        case Token::Kind::Minus:
            if (imm(node, right)) // constant folding
                node = IRNode(IRNode::Kind::Imm, node.val - right.val, t.loc);
            else
                node = IRNode(IRNode::Op::Sub, std::move(node), std::move(right), t.loc);
            break;
        default:
            break;
        }
    }
    return node;
}

IRNode Parser::sum()
{
    IRNode node = factor();
    while (sym == Token::Kind::Times || sym == Token::Kind::Div)
    {
        scan();
        Token::Kind op = t.kind;
        IRNode right = factor();
        switch (op)
        {
        case Token::Kind::Times:
            if (imm(node, right)) // constant folding
                node = IRNode(IRNode::Kind::Imm, node.val * right.val, t.loc);
            else
                node = IRNode(IRNode::Op::Mul, std::move(node), std::move(right), t.loc);
            break;
        case Token::Kind::Div:
            if (imm(node, right)) // constant folding
                node = IRNode(IRNode::Kind::Imm, node.val / right.val, t.loc);
            else
                node = IRNode(IRNode::Op::Div, std::move(node), std::move(right), t.loc);
            break;
        default:
            break;
        }
    }
    return node;
}

IRNode Parser::factor()
{
    if (sym == Token::Kind::Lpar)
    {
        scan();
        IRNode node = expr();
        check(Token::Kind::Rpar);
        return node;
    } else
        return value();
}

IRNode Parser::value()
{
    if (sym == Token::Kind::Number || sym == Token::Kind::Minus)
    {
        scan();
        bool neg = false;
        if (t.kind == Token::Kind::Minus)
        {
            neg = true;
            check(Token::Kind::Number);
        }
        float val = strtof(((neg ? "-"s : ""s) + t.str).c_str(), nullptr);
        return IRNode(IRNode::Kind::Imm, val, t.loc);
    }
    else if (sym == Token::Kind::Ident)
    {
        IRNode call = Parser::call();
        if (sym == Token::Kind::Period)
        {
            scan();
            check(Token::Kind::Ident);
            return IRNode(IRNode::Kind::Swizzle, std::string(t.str), std::move(call), t.loc);
        }
        return call;
    }
    else
    {
        error("expected number|call, was %s", Token::KindToStr(sym).data());
        return IRNode();
    }
}

std::list<IRNode> Parser::parse()
{
    std::list<IRNode> result;
    scan();
    while (sym == Token::Kind::Lf)
        scan();
    result.push_back(call());
    while (sym == Token::Kind::Lf)
    {
        while (sym == Token::Kind::Lf)
            scan();
        if (sym != Token::Kind::Eof)
            result.push_back(call());
    }
    while (sym == Token::Kind::Lf)
        scan();
    check(Token::Kind::Eof);

    if (hecl::VerbosityLevel > 1)
        for (auto& res : result)
            printf("%s\n", res.toString().c_str());

    return result;
}

}