glisp

-module(glisp@eval).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([eval/2]).

-if(?OTP_RELEASE >= 27).
-define(MODULEDOC(Str), -moduledoc(Str)).
-define(DOC(Str), -doc(Str)).
-else.
-define(MODULEDOC(Str), -compile([])).
-define(DOC(Str), -compile([])).
-endif.

-file("src/glisp/eval.gleam", 56).
-spec apply_function(glisp@ast:expr(), list(glisp@ast:expr())) -> {ok,
        glisp@ast:expr()} |
    {error, binary()}.
apply_function(Func, Args) ->
    case Func of
        {builtin, Fn_impl} ->
            Fn_impl(Args);

        _ ->
            {error,
                <<"Not a function "/utf8,
                    (glisp@ast:expr_to_string(Func))/binary>>}
    end.

-file("src/glisp/eval.gleam", 63).
-spec is_truthy(glisp@ast:expr()) -> boolean().
is_truthy(Expr) ->
    case Expr of
        {number, 0} ->
            false;

        {list, []} ->
            false;

        _ ->
            true
    end.

-file("src/glisp/eval.gleam", 52).
?DOC(" Evaluate a list of expressions\n").
-spec eval_list(
    list(glisp@ast:expr()),
    gleam@dict:dict(binary(), glisp@ast:expr())
) -> {ok, list(glisp@ast:expr())} | {error, binary()}.
eval_list(Exprs, Env) ->
    gleam@list:try_map(Exprs, fun(Expr) -> eval(Expr, Env) end).

-file("src/glisp/eval.gleam", 13).
?DOC(
    " Evaluate an expression in the given environment\n"
    "\n"
    " This function is the core of the interpreter, handling different expression types:\n"
    " - Numbers evaluate to themselves\n"
    " - Atoms are looked up in the environment\n"
    " - Built-in functions return themselves\n"
    " - Lists handle special forms (`define`, `if`) or function application\n"
).
-spec eval(glisp@ast:expr(), gleam@dict:dict(binary(), glisp@ast:expr())) -> {ok,
        glisp@ast:expr()} |
    {error, binary()}.
eval(Expr, Env) ->
    case Expr of
        {number, _} ->
            {ok, Expr};

        {atom, Name} ->
            glisp@environment:get(Env, Name);

        {builtin, _} ->
            {ok, Expr};

        {list, Elements} ->
            case Elements of
                [] ->
                    {ok, Expr};

                [{atom, <<"define"/utf8>>}, {atom, Name@1}, Value_expr] ->
                    _pipe = eval(Value_expr, Env),
                    gleam@result:map(
                        _pipe,
                        fun(Value) ->
                            _ = glisp@environment:set(Env, Name@1, Value),
                            Value
                        end
                    );

                [{atom, <<"if"/utf8>>}, Condition, Then_expr, Else_expr] ->
                    _pipe@1 = eval(Condition, Env),
                    gleam@result:then(
                        _pipe@1,
                        fun(Cond_val) -> case is_truthy(Cond_val) of
                                true ->
                                    eval(Then_expr, Env);

                                false ->
                                    eval(Else_expr, Env)
                            end end
                    );

                [Func_expr | Args] ->
                    _pipe@2 = eval(Func_expr, Env),
                    gleam@result:then(
                        _pipe@2,
                        fun(Func) -> _pipe@3 = eval_list(Args, Env),
                            gleam@result:then(
                                _pipe@3,
                                fun(Evaluated_args) ->
                                    apply_function(Func, Evaluated_args)
                                end
                            ) end
                    )
            end
    end.