Add liberator.assert.

2025-12-21 00:28:00 +01:00 · 2009-11-03 02:36:48 -05:00
parent 34e9b10fb9
commit 1ce498401e
13 changed files with 154 additions and 152 deletions
--- a/common/content/bookmarks.js
+++ b/common/content/bookmarks.js
@@ -1126,11 +1126,9 @@ function QuickMarks() //{{{
        function (args)
        {
            // TODO: finish arg parsing - we really need a proper way to do this. :)
-            if (!args.bang && !args.string)
-                return void liberator.echoerr("E471: Argument required");
-
-            if (args.bang && args.string)
-                return void liberator.echoerr("E474: Invalid argument");
+            // assert(args.bang ^ args.string)
+            liberator.assert( args.bang ||  args.string, "E471: Argument required");
+            liberator.assert(!args.bang || !args.string, "E474: Invalid argument");

            if (args.bang)
                quickmarks.removeAll();
@@ -1167,8 +1165,7 @@ function QuickMarks() //{{{
            args = args.string;

            // ignore invalid qmark characters unless there are no valid qmark chars
-            if (args && !/[a-zA-Z0-9]/.test(args))
-                return void liberator.echoerr("E283: No QuickMarks matching \"" + args + "\"");
+            liberator.assert(!args || /[a-zA-Z0-9]/.test(args), "E283: No QuickMarks matching \"" + args + "\"");

            let filter = args.replace(/[^a-zA-Z0-9]/g, "");
            quickmarks.list(filter);
@@ -1253,14 +1250,12 @@ function QuickMarks() //{{{

            marks = Array.concat(lowercaseMarks, uppercaseMarks, numberMarks);

-            if (marks.length == 0)
-                return void liberator.echoerr("No QuickMarks set");
+            liberator.assert(marks.length > 0, "No QuickMarks set");

            if (filter.length > 0)
            {
                marks = marks.filter(function (qmark) filter.indexOf(qmark) >= 0);
-                if (marks.length == 0)
-                    return void liberator.echoerr("E283: No QuickMarks matching \"" + filter + "\"");
+                liberator.assert(marks.length >= 0, "E283: No QuickMarks matching \"" + filter + "\"");
            }

            let items = [[mark, qmarks.get(mark)] for ([k, mark] in Iterator(marks))];
--- a/common/content/buffer.js
+++ b/common/content/buffer.js
@@ -28,8 +28,8 @@ function Buffer() //{{{

    function setZoom(value, fullZoom)
    {
-        if (value < ZOOM_MIN || value > ZOOM_MAX)
-            return void liberator.echoerr("Zoom value out of range (" + ZOOM_MIN + " - " + ZOOM_MAX + "%)");
+        liberator.assert(value >= ZOOM_MIN && value <= ZOOM_MAX,
+            "Zoom value out of range (" + ZOOM_MIN + " - " + ZOOM_MAX + "%)");

        ZoomManager.useFullZoom = fullZoom;
        ZoomManager.zoom = value / 100;
@@ -534,8 +534,8 @@ function Buffer() //{{{
            let arg = args[0];

            // FIXME: arg handling is a bit of a mess, check for filename
-            if (arg && (liberator.has("Win32") || arg[0] != ">"))
-                return void liberator.echoerr("E488: Trailing characters");
+            liberator.assert(!arg || arg[0] == ">" && !liberator.has("Win32"),
+                "E488: Trailing characters");

            options.withContext(function () {
                if (arg)
@@ -584,8 +584,8 @@ function Buffer() //{{{

            let titles = buffer.alternateStyleSheets.map(function (stylesheet) stylesheet.title);

-            if (arg && titles.indexOf(arg) == -1)
-                return void liberator.echoerr("E475: Invalid argument: " + arg);
+            liberator.assert(!arg || titles.indexOf(arg) >= 0,
+                "E475: Invalid argument: " + arg);

            if (options["usermode"])
                options["usermode"] = false;
@@ -619,8 +619,8 @@ function Buffer() //{{{
            {
                let file = io.File(filename);

-                if (file.exists() && !args.bang)
-                    return void liberator.echoerr("E13: File exists (add ! to override)");
+                liberator.assert(!file.exists() || args.bang,
+                    "E13: File exists (add ! to override)");

                chosenData = { file: file, uri: window.makeURI(doc.location.href, doc.characterSet) };
            }
@@ -685,7 +685,7 @@ function Buffer() //{{{
                level = util.Math.constrain(level, ZOOM_MIN, ZOOM_MAX);
            }
            else
-                return void liberator.echoerr("E488: Trailing characters");
+                liberator.assert(false, "E488: Trailing characters");

            if (args.bang)
                buffer.fullZoom = level;
@@ -1701,10 +1701,10 @@ function Marks() //{{{
            let special = args.bang;
            args = args.string;

-            if (!special && !args)
-                return void liberator.echoerr("E471: Argument required");
-            if (special && args)
-                return void liberator.echoerr("E474: Invalid argument");
+            // assert(special ^ args)
+            liberator.assert( special ||  args, "E471: Argument required");
+            liberator.assert(!special || !args, "E474: Invalid argument");
+
            let matches;
            if (matches = args.match(/(?:(?:^|[^a-zA-Z0-9])-|-(?:$|[^a-zA-Z0-9])|[^a-zA-Z0-9 -]).*/))
            {
@@ -1744,10 +1744,10 @@ function Marks() //{{{
        function (args)
        {
            let mark = args[0];
-            if (mark.length > 1)
-                return void liberator.echoerr("E488: Trailing characters");
-            if (!/[a-zA-Z]/.test(mark))
-                return void liberator.echoerr("E191: Argument must be a letter or forward/backward quote");
+
+            liberator.assert(mark.length <= 1, "E488: Trailing characters");
+            liberator.assert(/[a-zA-Z]/.test(mark),
+                "E191: Argument must be a letter or forward/backward quote");

            marks.add(mark);
        },
@@ -1760,8 +1760,8 @@ function Marks() //{{{
            args = args.string;

            // ignore invalid mark characters unless there are no valid mark chars
-            if (args && !/[a-zA-Z]/.test(args))
-                return void liberator.echoerr("E283: No marks matching " + args.quote());
+            liberator.assert(!args || /[a-zA-Z]/.test(args),
+                "E283: No marks matching " + args.quote());

            let filter = args.replace(/[^a-zA-Z]/g, "");
            marks.list(filter);
@@ -1941,14 +1941,12 @@ function Marks() //{{{
        {
            let marks = getSortedMarks();

-            if (marks.length == 0)
-                return void liberator.echoerr("No marks set");
+            liberator.assert(marks.length > 0, "No marks set");

            if (filter.length > 0)
            {
                marks = marks.filter(function (mark) filter.indexOf(mark[0]) >= 0);
-                if (marks.length == 0)
-                    return void liberator.echoerr("E283: No marks matching " + filter.quote());
+                liberator.assert(marks.length > 0, "E283: No marks matching " + filter.quote());
            }

            let list = template.tabular(
--- a/common/content/commands.js
+++ b/common/content/commands.js
@@ -189,7 +189,7 @@ Command.prototype = {
                return;
            args.count = count;
            args.bang = bang;
-            self.action.call(self, args, modifiers);
+            liberator.trapErrors(self.action, self, args, modifiers)
        }

        if (this.hereDoc)
@@ -714,8 +714,7 @@ function Commands() //{{{
                                if (sep == "=" || /\s/.test(sep) && opt[1] != this.OPTION_NOARG)
                                {
                                    [count, arg, quote, error] = getNextArg(sub.substr(optname.length + 1));
-                                    if (error)
-                                        return void liberator.echoerr(error);
+                                    liberator.assert(!error, error);

                                    // if we add the argument to an option after a space, it MUST not be empty
                                    if (sep != "=" && !quote && arg.length == 0)
@@ -808,8 +807,7 @@ function Commands() //{{{

                // if not an option, treat this token as an argument
                let [count, arg, quote, error] = getNextArg(sub);
-                if (error)
-                    return void liberator.echoerr(error);
+                liberator.assert(!error, error);

                if (complete)
                {
@@ -1018,8 +1016,7 @@ function Commands() //{{{
        {
            let cmd = args[0];

-            if (cmd != null && /\W/.test(cmd))
-                return void liberator.echoerr("E182: Invalid command name");
+            liberator.assert(!/\W/.test(cmd || ''), "E182: Invalid command name");

            if (args.literalArg)
            {
--- a/common/content/editor.js
+++ b/common/content/editor.js
@@ -177,8 +177,8 @@ function Editor() //{{{
            function (args)
            {
                let matches = args.string.match(RegExp("^\\s*($|" + abbrevmatch + ")(?:\\s*$|\\s+(.*))"));
-                if (!matches)
-                    return void liberator.echoerr("E474: Invalid argument");
+                liberator.assert(matches, "E474: Invalid argument");
+
                let [, lhs, rhs] = matches;
                if (rhs)
                    editor.addAbbreviation(mode, lhs, rhs);
@@ -844,8 +844,7 @@ function Editor() //{{{
            // TODO: save return value in v:shell_error
            let args = commands.parseArgs(options["editor"], [], "*", true);

-            if (args.length < 1)
-                return void liberator.echoerr("No editor specified");
+            liberator.assert(args.length >= 1, "No editor specified");

            args.push(path);
            liberator.callFunctionInThread(null, io.run, io.expandPath(args.shift()), args, true);
--- a/common/content/events.js
+++ b/common/content/events.js
@@ -56,7 +56,7 @@ function AutoCommands() //{{{
            }
            catch (e)
            {
-                return void liberator.echoerr("E475: Invalid argument: " + regex);
+                liberator.assert(false, "E475: Invalid argument: " + regex);
            }

            if (event)
@@ -66,8 +66,8 @@ function AutoCommands() //{{{
                validEvents.push("*");

                events = event.split(",");
-                if (!events.every(function (event) validEvents.indexOf(event) >= 0))
-                    return void liberator.echoerr("E216: No such group or event: " + event);
+                liberator.assert(events.every(function (event) validEvents.indexOf(event) >= 0),
+                    "E216: No such group or event: " + event);
            }

            if (cmd) // add new command, possibly removing all others with the same event/pattern
@@ -124,12 +124,12 @@ function AutoCommands() //{{{
                let validEvents = config.autocommands.map(function (e) e[0]);

                // TODO: add command validators
-                if (event == "*")
-                    return void liberator.echoerr("E217: Can't execute autocommands for ALL events");
-                else if (validEvents.indexOf(event) == -1)
-                    return void liberator.echoerr("E216: No such group or event: " + args);
-                else if (!autocommands.get(event).some(function (c) c.pattern.test(defaultURL)))
-                    return void liberator.echomsg("No matching autocommands");
+                liberator.assert(event != "*",
+                    "E217: Can't execute autocommands for ALL events");
+                liberator.assert(validEvents.indexOf(event) >= 0,
+                    "E216: No such group or event: " + args);
+                liberator.assert(autocommands.get(event).some(function (c) c.pattern.test(defaultURL)),
+                    "No matching autocommands");

                if (this.name == "doautoall" && liberator.has("tabs"))
                {
@@ -649,8 +649,7 @@ function Events() //{{{
        "Delete macros",
        function (args)
        {
-            if (args.bang && args.string)
-                return void liberator.echoerr("E474: Invalid argument");
+            liberator.assert(!args.bang || !args.string, "E474: Invalid argument");

            if (args.bang)
                events.deleteMacros();
@@ -724,9 +723,9 @@ function Events() //{{{
         */
        startRecording: function (macro)
        {
-            if (!/[a-zA-Z0-9]/.test(macro))
                // TODO: ignore this like Vim?
-                return void liberator.echoerr("E354: Invalid register name: '" + macro + "'");
+            liberator.assert(/[a-zA-Z0-9]/.test(macro),
+                "E354: Invalid register name: '" + macro + "'");

            modes.isRecording = true;

--- a/common/content/finder.js
+++ b/common/content/finder.js
@@ -417,10 +417,8 @@ function Finder() //{{{
                var pattern = str;
            else
            {
-                if (lastSearchPattern)
+                liberator.assert(lastSearchPattern, "E35: No previous search pattern");
                pattern = lastSearchPattern;
-                else
-                    return void liberator.echoerr("E35: No previous search pattern");
            }

            this.clear();
--- a/common/content/io.js
+++ b/common/content/io.js
@@ -189,10 +189,8 @@ function IO() //{{{
                arg = "~";
            else if (arg == "-")
            {
-                if (oldcwd)
+                liberator.assert(oldcwd, "E186: No previous directory");
                arg = oldcwd.path;
-                else
-                    return void liberator.echoerr("E186: No previous directory");
            }

            arg = io.expandPath(arg);
@@ -252,14 +250,13 @@ function IO() //{{{
        "Write current key mappings and changed options to the config file",
        function (args)
        {
-            if (args.length > 1)
-                return void liberator.echoerr("E172: Only one file name allowed");
+            liberator.assert(args.length <= 1, "E172: Only one file name allowed");

            let filename = args[0] || io.getRCFile(null, true).path;
            let file = io.File(filename);

-            if (file.exists() && !args.bang)
-                return void liberator.echoerr("E189: \"" + filename + "\" exists (add ! to override)");
+            liberator.assert(!file.exists() || args.bang,
+                "E189: \"" + filename + "\" exists (add ! to override)");

            // TODO: Use a set/specifiable list here:
            let lines = [cmd.serial().map(commands.commandToString) for (cmd in commands) if (cmd.serial)];
@@ -341,8 +338,8 @@ function IO() //{{{
                arg = "!" + arg;

            // replaceable bang and no previous command?
-            if (/((^|[^\\])(\\\\)*)!/.test(arg) && !lastRunCommand)
-                return void liberator.echoerr("E34: No previous command");
+            liberator.assert(!/((^|[^\\])(\\\\)*)!/.test(arg) || lastRunCommand,
+                "E34: No previous command");

            // NOTE: Vim doesn't replace ! preceded by 2 or more backslashes and documents it - desirable?
            // pass through a raw bang when escaped or substitute the last command
--- a/common/content/liberator.js
+++ b/common/content/liberator.js
@@ -15,6 +15,13 @@ const EVAL_ERROR = "__liberator_eval_error";
 const EVAL_RESULT = "__liberator_eval_result";
 const EVAL_STRING = "__liberator_eval_string";

+function FailedAssertion(message) {
+    this.message = message;
+}
+FailedAssertion.prototype = {
+    __proto__: Error.prototype,
+};
+
 const liberator = (function () //{{{
 {
    ////////////////////////////////////////////////////////////////////////////////
@@ -363,8 +370,8 @@ const liberator = (function () //{{{
                let arg = args.literalArg;
                let items = getMenuItems();

-                if (!items.some(function (i) i.fullMenuPath == arg))
-                    return void liberator.echoerr("E334: Menu not found: " + arg);
+                liberator.assert(items.some(function (i) i.fullMenuPath == arg),
+                    "E334: Menu not found: " + arg);

                for (let [, item] in Iterator(items))
                {
@@ -453,8 +460,7 @@ const liberator = (function () //{{{
                        liberator.extensions.forEach(function (e) { action(e); });
                    else
                    {
-                        if (!name)
-                            return void liberator.echoerr("E471: Argument required"); // XXX
+                        liberator.assert(name, "E471: Argument required"); // XXX

                        let extension = liberator.getExtension(name);
                        if (extension)
@@ -481,8 +487,8 @@ const liberator = (function () //{{{
            function (args)
            {
                let extension = liberator.getExtension(args[0]);
-                if (!extension || !extension.options)
-                    return void liberator.echoerr("E474: Invalid argument");
+                liberator.assert(extension && extension.options,
+                    "E474: Invalid argument");
                if (args.bang)
                    window.openDialog(extension.options, "_blank", "chrome");
                else
@@ -554,8 +560,7 @@ const liberator = (function () //{{{
                command.description,
                function (args)
                {
-                    if (args.bang)
-                        return void liberator.echoerr("E478: Don't panic!");
+                    liberator.assert(!args.bang, "E478: Don't panic!");

                    liberator.help(args.literalArg, unchunked);
                },
@@ -665,8 +670,7 @@ const liberator = (function () //{{{
                    function (args)
                    {
                        let toolbar = findToolbar(args[0]);
-                        if (!toolbar)
-                            return void liberator.echoerr("E474: Invalid argument");
+                        liberator.assert(toolbar, "E474: Invalid argument");
                        action(toolbar);
                    },
                    {
@@ -1103,6 +1107,20 @@ const liberator = (function () //{{{
            liberator.dump((msg || "Stack") + "\n" + stack);
        },

+        /**
+         * Tests a condition and throws a FailedAssertion error on
+         * failure.
+         *
+         * @param {boolean} condition The condition to test.
+         * @param {string}  message The message to present to the
+         *                          user on failure.
+         */
+        assert: function (condition, message)
+        {
+            if (!condition)
+                throw new FailedAssertion(message);
+        },
+
        /**
         * Outputs a plain message to the command line.
         *
@@ -1300,8 +1318,7 @@ const liberator = (function () //{{{
            else if (special && !command.bang)
                err = "E477: No ! allowed";

-            if (err)
-                return void liberator.echoerr(err);
+            liberator.assert(!err, err);
            if (!silent)
                commandline.command = str.replace(/^\s*:\s*/, "");

@@ -1509,8 +1526,7 @@ const liberator = (function () //{{{
            }

            let page = this.findHelp(topic, unchunked);
-            if (page == null)
-                return void liberator.echoerr("E149: Sorry, no help for " + topic);
+            liberator.assert(page != null, "E149: Sorry, no help for " + topic);

            liberator.open("liberator://help/" + page, { from: "help" });
            if (options.get("activate").has("all", "help"))
@@ -1530,8 +1546,7 @@ const liberator = (function () //{{{
        {
            function sourceDirectory(dir)
            {
-                if (!dir.isReadable())
-                    return void liberator.echoerr("E484: Can't open file " + dir.path);
+                liberator.assert(dir.isReadable(), "E484: Can't open file " + dir.path);

                liberator.log("Sourcing plugin directory: " + dir.path + "...", 3);
                dir.readDirectory(true).forEach(function (file) {
@@ -1752,6 +1767,25 @@ const liberator = (function () //{{{
                window.goQuitApplication();
        },

+        /**
+         * Traps errors in the called function, possibly reporting them.
+         *
+         * @param {function} func The function to call
+         * @param {object} self The 'this' object for the function.
+         */
+        trapErrors: function (func, self)
+        {
+            try
+            {
+                return func.apply(self || this, Array.slice(arguments, 2));
+            }
+            catch (e)
+            {
+                if (e instanceof FailedAssertion)
+                    liberator.echoerr(e.message);
+            }
+        },
+
        /**
         * Reports an error to both the console and the host application's
         * Error Console.
--- a/common/content/mappings.js
+++ b/common/content/mappings.js
@@ -105,11 +105,11 @@ Map.prototype = {
            args.push(argument);

        let self = this;
-        // FIXME: Kludge.
-        if (this.names[0] != ".")
-            mappings.repeat = function () self.action.apply(self, args);
+        function repeat() self.action.apply(self, args);
+        if (this.names[0] != ".") // FIXME: Kludge.
+            mappings.repeat = repeat;

-        return this.action.apply(this, args);
+        return liberator.trapErrors(repeat);
    }

 }; //}}}
--- a/common/content/options.js
+++ b/common/content/options.js
@@ -200,14 +200,13 @@ Option.prototype = {
            scope = this.scope;

        let aValue;
-
        if (liberator.has("tabs") && (scope & options.OPTION_SCOPE_LOCAL))
            aValue = tabs.options[this.name];
        if ((scope & options.OPTION_SCOPE_GLOBAL) && (aValue == undefined))
            aValue = this.globalValue;

        if (this.getter)
-            return this.getter.call(this, aValue);
+            return liberator.trapErrors(this.getter, this, aValue);

        return aValue;
    },
@@ -228,7 +227,7 @@ Option.prototype = {
            return null;

        if (this.setter)
-            newValue = this.setter(newValue);
+            newValue = liberator.trapErrors(this.setter, this, newValue);

        if (liberator.has("tabs") && (scope & options.OPTION_SCOPE_LOCAL))
            tabs.options[this.name] = newValue;
@@ -581,12 +580,11 @@ function Options() //{{{
            }

            let opt = options.parseOpt(arg, modifiers);
-            if (!opt)
-                return void liberator.echoerr("Error parsing :set command: " + arg);
+            liberator.assert(opt, "Error parsing :set command: " + arg);

            let option = opt.option;
-            if (option == null && !opt.all)
-                return void liberator.echoerr("E518: Unknown option: " + arg);
+            liberator.assert(option != null || opt.all,
+                "E518: Unknown option: " + arg);

            // reset a variable to its default value
            if (opt.reset)
@@ -630,8 +628,7 @@ function Options() //{{{

                if (opt.option.type == "boolean")
                {
-                    if (opt.valueGiven)
-                        return void liberator.echoerr("E474: Invalid argument: " + arg);
+                    liberator.assert(!opt.valueGiven, "E474: Invalid argument: " + arg);
                    opt.values = !opt.unsetBoolean;
                }
                let res = opt.option.op(opt.operator || "=", opt.values, opt.scope, opt.invert);
@@ -769,14 +766,12 @@ function Options() //{{{
                if (!matches[1])
                {
                    let reference = liberator.variableReference(matches[2]);
-                    if (!reference[0] && matches[3])
-                        return void liberator.echoerr("E121: Undefined variable: " + matches[2]);
+                    liberator.assert(reference[0] || !matches[3],
+                        "E121: Undefined variable: " + matches[2]);

                    let expr = liberator.evalExpression(matches[4]);
-                    if (expr === undefined)
-                        return void liberator.echoerr("E15: Invalid expression: " + matches[4]);
-                    else
-                    {
+                    liberator.assert(expr !== undefined, "E15: Invalid expression: " + matches[4]);
+
                    if (!reference[0])
                    {
                        if (reference[2] == "g")
@@ -798,13 +793,11 @@ function Options() //{{{
                        reference[0][reference[1]] = expr;
                }
            }
-            }
            // 1 - name
            else if (matches = args.match(/^\s*([\w:]+)\s*$/))
            {
                let reference = liberator.variableReference(matches[1]);
-                if (!reference[0])
-                    return void liberator.echoerr("E121: Undefined variable: " + matches[1]);
+                liberator.assert(reference[0], "E121: Undefined variable: " + matches[1]);

                let value = reference[0][reference[1]];
                let prefix = typeof value == "number"   ? "#" :
--- a/common/content/sanitizer.js
+++ b/common/content/sanitizer.js
@@ -117,8 +117,7 @@ function Sanitizer() //{{{

            if (args.bang)
            {
-                if (args.length > 0)
-                    return void liberator.echoerr("E488: Trailing characters");
+                liberator.assert(args.length == 0, "E488: Trailing characters");

                liberator.log("Sanitizing all items in 'sanitizeitems'...");

@@ -132,8 +131,7 @@ function Sanitizer() //{{{
            }
            else
            {
-                if (args.length == 0)
-                    return void liberator.echoerr("E471: Argument required");
+                liberator.assert(args.length > 0, "E471: Argument required");

                for (let [, item] in Iterator(args.map(argToPref)))
                {
--- a/common/content/style.js
+++ b/common/content/style.js
@@ -640,8 +640,9 @@ liberator.registerObserver("load_commands", function () {

            if (scheme == "default")
                highlight.clear();
-            else if (!io.sourceFromRuntimePath(["colors/" + scheme + ".vimp"]))
-                return void liberator.echoerr("E185: Cannot find color scheme " + scheme);
+            else
+                liberator.assert(!io.sourceFromRuntimePath(["colors/" + scheme + ".vimp"]),
+                    "E185: Cannot find color scheme " + scheme);
            autocommands.trigger("ColorScheme", { name: scheme });
        },
        {
--- a/common/content/tabs.js
+++ b/common/content/tabs.js
@@ -431,10 +431,8 @@ function Tabs() //{{{
                // count is ignored if an arg is specified, as per Vim
                if (arg)
                {
-                    if (/^\d+$/.test(arg))
+                    liberator.assert(/^\d+$/.test(arg), "E488: Trailing characters");
                    index = arg - 1;
-                    else
-                        return void liberator.echoerr("E488: Trailing characters");
                }
                else
                    index = count - 1;
@@ -527,8 +525,8 @@ function Tabs() //{{{
                let arg = args[0];

                // FIXME: tabmove! N should probably produce an error
-                if (arg && !/^([+-]?\d+)$/.test(arg))
-                    return void liberator.echoerr("E488: Trailing characters");
+                liberator.assert(!arg || /^([+-]?\d+)$/.test(arg),
+                    "E488: Trailing characters");

                // if not specified, move to after the last tab
                tabs.move(getBrowser().mCurrentTab, arg || "$", args.bang);
@@ -567,8 +565,7 @@ function Tabs() //{{{
            "Detach current tab to its own window",
            function ()
            {
-                if (tabs.count == 1)
-                    return void liberator.echoerr("Can't detach the last tab");
+                liberator.assert(tabs.count > 1, "Can't detach the last tab");

                tabs.detachTab(null);
            },
@@ -600,16 +597,14 @@ function Tabs() //{{{
            "Attach the current tab to another window",
            function (args)
            {
-                if (args.length > 2 || args.some(function (i) i && !/^\d+$/.test(i)))
-                    return void liberator.echoerr("E488: Trailing characters");
+                liberator.assert(args.length <= 2 && !args.some(function (i) i && !/^\d+$/.test(i)),
+                    "E488: Trailing characters");

                let [winIndex, tabIndex] = args.map(parseInt);
                let win = liberator.windows[winIndex - 1];

-                if (!win)
-                    return void liberator.echoerr("Window " + winIndex + " does not exist");
-                else if (win == window)
-                    return void liberator.echoerr("Can't reattach to the same window");
+                liberator.assert(win, "Window " + winIndex + " does not exist");
+                liberator.assert(win != window, "Can't reattach to the same window");

                let browser = win.getBrowser();
                let dummy = browser.addTab("about:blank");
@@ -1192,8 +1187,8 @@ function Tabs() //{{{
         */
        selectAlternateTab: function ()
        {
-            if (tabs.alternate == null || tabs.getTab() == tabs.alternate)
-                return void liberator.echoerr("E23: No alternate page");
+            liberator.assert(tabs.alternate != null && tabs.getTab() != tabs.alternate,
+                "E23: No alternate page");

            // NOTE: this currently relies on v.tabs.index() returning the
            // currently selected tab index when passed null
@@ -1202,9 +1197,7 @@ function Tabs() //{{{
            // TODO: since a tab close is more like a bdelete for us we
            // should probably reopen the closed tab when a 'deleted'
            // alternate is selected
-            if (index == -1)
-                liberator.echoerr("E86: Buffer does not exist");  // TODO: This should read "Buffer N does not exist"
-            else
+            liberator.assert(index >= 0, "E86: Buffer does not exist");  // TODO: This should read "Buffer N does not exist"
            tabs.select(index);
        },