mal/d/step4_if_fn_do.d

module main;

import std.algorithm;
import std.array;
import std.range;
import std.stdio;
import std.string;
import env;
import mal_core;
import readline;
import reader;
import printer;
import types;

MalType READ(string str)
{
    return read_str(str);
}

MalType eval_ast(MalType ast, Env env)
{
    if (typeid(ast) == typeid(MalSymbol))
    {
        auto sym = verify_cast!MalSymbol(ast);
        return env.get(sym);
    }
    else if (typeid(ast) == typeid(MalList))
    {
        auto lst = verify_cast!MalList(ast);
        auto el = array(lst.elements.map!(e => EVAL(e, env)));
        return new MalList(el);
    }
    else if (typeid(ast) == typeid(MalVector))
    {
        auto lst = verify_cast!MalVector(ast);
        auto el = array(lst.elements.map!(e => EVAL(e, env)));
        return new MalVector(el);
    }
    else if (typeid(ast) == typeid(MalHashmap))
    {
        auto hm = verify_cast!MalHashmap(ast);
        typeof(hm.data) new_data;
        foreach (string k, MalType v; hm.data)
        {
            new_data[k] = EVAL(v, env);
        }
        return new MalHashmap(new_data);
    }
    else
    {
        return ast;
    }
}

MalType EVAL(MalType ast, Env env)
{
    MalList ast_list = cast(MalList) ast;
    if (ast_list is null)
    {
        return eval_ast(ast, env);
    }

    auto aste = ast_list.elements;
    if (aste.length == 0)
    {
        return ast;
    }
    auto a0_sym = cast(MalSymbol) aste[0];
    auto sym_name = a0_sym is null ? "" : a0_sym.name;
    switch (sym_name)
    {
        case "def!":
            auto a1 = verify_cast!MalSymbol(aste[1]);
            return env.set(a1, EVAL(aste[2], env));

        case "let*":
            auto a1 = verify_cast!MalSequential(aste[1]);
            auto let_env = new Env(env);
            foreach (kv; chunks(a1.elements, 2))
            {
                if (kv.length < 2) throw new Exception("let* requires even number of elements");
                auto var_name = verify_cast!MalSymbol(kv[0]);
                let_env.set(var_name, EVAL(kv[1], let_env));
            }
            return EVAL(aste[2], let_env);

        case "do":
            auto rest = new MalList(aste[1..$]);
            auto el = verify_cast!MalList(eval_ast(rest, env));
            return el.elements[$-1];

        case "if":
            auto cond = EVAL(aste[1], env);
            if (cond.is_truthy())
                return EVAL(aste[2], env);
            else
                if (aste.length > 3)
                    return EVAL(aste[3], env);
                else
                    return mal_nil;

        case "fn*":
            auto args_list = verify_cast!MalSequential(aste[1]);
            return new MalFunc(args_list.elements, aste[2], env);

        default:
            auto el = verify_cast!MalList(eval_ast(ast, env));
            if (el.elements.length == 0)
            {
                throw new Exception("Expected a non-empty list");
            }
            auto first = el.elements[0];
            auto rest = el.elements[1..$];
            if (typeid(first) == typeid(MalFunc))
            {
                auto funcobj = verify_cast!MalFunc(first);
                auto callenv = new Env(funcobj.def_env, funcobj.arg_names, rest);
                return EVAL(funcobj.func_body, callenv);
            }
            else if (typeid(first) == typeid(MalBuiltinFunc))
            {
                auto builtinfuncobj = verify_cast!MalBuiltinFunc(first);
                return builtinfuncobj.fn(rest);
            }
            else
            {
                throw new Exception("Expected a function");
            }
    }
}

string PRINT(MalType ast)
{
    return pr_str(ast);
}

MalType re(string str, Env env)
{
    return EVAL(READ(str), env);
}

string rep(string str, Env env)
{
    return PRINT(re(str, env));
}

void main()
{
    auto repl_env = new Env(null);
    foreach (string sym_name, BuiltinStaticFuncType f; core_ns)
    {
        repl_env.set(new MalSymbol(sym_name), new MalBuiltinFunc(f, sym_name));
    }

    // core.mal: defined using the language itself
    re("(def! not (fn* (a) (if a false true)))", repl_env);

    for (;;)
    {
        string line = _readline("user> ");
        if (line is null) break;
        if (line.length == 0) continue;
        try
        {
            writeln(rep(line, repl_env));
        }
        catch (Exception e)
        {
            writeln("Error: ", e.msg);
        }
    }
    writeln("");
}