clean up usage for repl

src/main.zig

@@ -17,7 +17,29 @@
 const std = @import("std");
 const mem = @import("memory.zig");
 const cpu_ = @import("cpu.zig");
+
 var long_prompt = false;
+
+const TOO_MANY_ARGUMENTS = "Wrong number of arguments";
+const WRONG_ARGUMENT = "Invalid argument";
+// COMMAND
+const PROMPT_COMMAND = "prompt";
+const SEGMENT_REGISTER_COMMAND = "sr";
+const REGISTER_COMMAND = "reg";
+const CLEAR_COMMAND = "cls";
+const HELP_COMMAND = "?";
+// DESCRIPTION
+const PROMPT_DESCRIPTION = "Change the prompt between Long-mode or Short-mode.";
+const REGISTER_DESCRIPTION = "Print the current values for Registers.";
+const SEGMENT_REGISTER_DESCRIPTION = "Print the current values for Segment Registers.";
+const CLEAR_DESCRIPTION = "Clears the screen.";
+// USAGE
+const PROMPT_USAGE = "prompt {short|long}";
+const REGISTER_USAGE = "reg";
+const SEGMENT_REGISTER_USAGE = "sr";
+const HELP_USAGE = "?";
+const CLEAR_USAGE = "cls";
+
 pub fn main() !void {
     var memory = mem.Memory.init();
     var cpu = cpu_.Cpu.init();
@@ -58,7 +80,11 @@ pub fn main() !void {
                 try handleSegmentRegisterCommand(&cpu, &it);
             } else if (std.mem.eql(u8, first_argument, "prompt")) {
                 try handlePromptCommand(&it);
-            } else if (std.mem.eql(u8, first_argument, "?")) {}
+            } else if (std.mem.eql(u8, first_argument, "?")) {
+                try handleHelpCommand(&it);
+            } else if (std.mem.eql(u8, first_argument, CLEAR_COMMAND)) {
+                try handleClearScreenCommand(&it);
+            }
         } else {
             // noop
         }
@@ -113,6 +139,28 @@ fn printSr(cpu: *cpu_.Cpu) void {
     });
 }
 
+fn handleHelpCommand(it: anytype) !void {
+    if (it.next()) |_| {
+        std.debug.print(
+            \\{s}. {s}
+            \\
+        , .{ TOO_MANY_ARGUMENTS, HELP_USAGE });
+    } else {
+        std.debug.print(
+            \\{s: <20} {s}
+            \\{s: <20} {s}
+            \\{s: <20} {s}
+            \\{s: <20} {s}
+            \\
+        , .{
+            PROMPT_USAGE,           PROMPT_DESCRIPTION,
+            REGISTER_USAGE,         REGISTER_DESCRIPTION,
+            SEGMENT_REGISTER_USAGE, SEGMENT_REGISTER_DESCRIPTION,
+            CLEAR_USAGE,            CLEAR_DESCRIPTION,
+        });
+    }
+}
+
 fn handlePromptCommand(it: anytype) !void {
     if (it.next()) |next_argument| {
         if (std.mem.eql(u8, next_argument, "long")) {
@@ -121,22 +169,42 @@ fn handlePromptCommand(it: anytype) !void {
             long_prompt = false;
         } else {
             std.debug.print(
-                \\Invalid argument. Usage: prompt <long|short>
+                \\{s}, usage: {s}
                 \\
-            , .{});
+            , .{ WRONG_ARGUMENT, PROMPT_USAGE });
         }
     } else {
         std.debug.print(
-            \\Invalid number of arguments. Usage: prompt <long|short>
+            \\{s}, usage: {s}
             \\
-        , .{});
+        , .{ TOO_MANY_ARGUMENTS, PROMPT_USAGE });
     }
 }
 
+fn handleRegisterCommand(cpu: *cpu_.Cpu, it: anytype) !void {
+    _ = cpu;
+    _ = it;
+}
+
 fn handleSegmentRegisterCommand(cpu: *cpu_.Cpu, it: anytype) !void {
     if (it.next()) |_| {
-        std.debug.print("Wrong number of arguments.\n", .{});
+        std.debug.print(
+            \\{s}, usage: {s}
+            \\
+        , .{ TOO_MANY_ARGUMENTS, SEGMENT_REGISTER_USAGE });
     } else {
         printSr(cpu);
     }
 }
+
+fn handleClearScreenCommand(it: anytype) !void {
+    var output = std.io.getStdOut().writer();
+    if (it.next()) |_| {
+        std.debug.print(
+            \\{s}, usage: {s}
+            \\
+        , .{ TOO_MANY_ARGUMENTS, CLEAR_USAGE });
+    } else {
+        try output.writeAll("\x1B[2J\x1B[H");
+    }
+}