main.zig

const std = @import("std");

// Errors which can be returned when parsing the command line arguments.
const ParseArgsError = error{TooManyArguments};

// The different commands which may be run.
const Command = union(enum) {
    startRepl,
    runInterpreter: []const u8,
};

pub fn main() anyerror!void {
    // initiate an memory allocator, which we wil free as soon as we
    // exit this scope.
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer arena.deinit();

    const allocator = arena.allocator();

    // get the commandline arguments
    const args = try std.process.argsAlloc(allocator);
    defer std.process.argsFree(allocator, args);

    const command = try parseArgs(args);
    switch (command) {
        Command.startRepl => std.debug.print("start the repl", .{}),
        Command.runInterpreter => |file| std.debug.print("running the file: {s}", .{file}),
    }
}

/// Parses the commandline arguments and returns the command to execute.
fn parseArgs(args: [][]const u8) ParseArgsError!Command {
    if (args.len > 2) return ParseArgsError.TooManyArguments;
    const action: Command = switch (args.len) {
        1 => Command.startRepl,
        else => Command{ .runInterpreter = args[1] },
    };
    return action;
}

test "no arguments should start the repl" {
    var arg: []const u8 = "lucy";
    const argsList = &[_][]const u8{arg};

    try std.testing.expectEqual(parseArgs(argsList), Command.startRepl);
}

test "extra argument should interpret the file" {
    var argOne: []const u8 = "lucy";
    var argTwo: []const u8 = "main.lucy";
    const argsList = &[_][]const u8{ argOne, argTwo };
    try std.testing.expectEqual(parseArgs(argsList), Command{ .runInterpreter = "main.lucy" });
}

test "too many arguments should raise an error" {
    var argOne: []const u8 = "lucy";
    var argTwo: []const u8 = "main.lucy";
    var argThree: []const u8 = "boo";
    const argsList = &[_][]const u8{ argOne, argTwo, argThree };

    try std.testing.expectError(ParseArgsError.TooManyArguments, parseArgs(argsList));
}