Add LastX command

The `LastX` implementation is not part of any RPL implementation that
I am aware of, but it is a staple of RPN. Implementing it in RPL might
make it easier to backport a few RPN programs.

Fixes: #384

Signed-off-by: Christophe de Dinechin <christophe@dinechin.org>

doc/commands/stack.md

@@ -35,6 +35,19 @@ Duplicate the same object twice on the stack
 ## DuplicateN (DUPN)
 Duplicate a group of N objects, N being given in stack level 1
 
+## LastArguments (LASTARG)
+Put the last arguments back on the stack
+
+## LastX
+Put the last first argument on the stack.
+
+This command does not exist on HP RPL calculators, and is here to make it easier
+to adapt RPN programs that use LastX a bit more often.
+
+## Undo
+Restore the stack to its last state before executing an interactive command.
+Note that this command can be used from a program, but it will restore the state
+prior to program execution.
 
 ## NDUPN
 Replicate one object N times and return N

fonts/EditorFont.cc

@@ -7,7 +7,7 @@ extern const unsigned char EditorFont_sparse_font_data[];
 const unsigned char EditorFont_sparse_font_data[73676] FONT_QSPI =
 {
 
-    0xBC, 0x02, 0xC7, 0xBF, 0x04, 0x36, 0x00, 0x01, 0x00, 0x2C, 0x01, 0x01, 0x00, 0x00, 0x0D, 0x01,
+    0xBD, 0x02, 0xC7, 0xBF, 0x04, 0x36, 0x00, 0x01, 0x00, 0x2C, 0x01, 0x01, 0x00, 0x00, 0x0D, 0x01,
     0x00, 0x2C, 0x01, 0x01, 0x08, 0x00, 0x20, 0x5F, 0x00, 0x2C, 0x01, 0x01, 0x08, 0x00, 0x02, 0x0B,
     0x05, 0x21, 0x09, 0xEF, 0xBD, 0xF7, 0xDE, 0x7B, 0xEF, 0xBD, 0xF7, 0xDE, 0x7B, 0xEF, 0xBD, 0xF7,
     0x1E, 0x00, 0x00, 0xB8, 0xFF, 0xFF, 0xFF, 0x0E, 0x03, 0x0B, 0x0B, 0x0F, 0x11, 0x8F, 0x7F, 0xFC,

fonts/HelpFont.cc

@@ -7,7 +7,7 @@ extern const unsigned char HelpFont_sparse_font_data[];
 const unsigned char HelpFont_sparse_font_data[15010] FONT_QSPI =
 {
 
-    0xBC, 0x02, 0x9E, 0x75, 0x14, 0x00, 0x01, 0x00, 0x11, 0x01, 0x01, 0x00, 0x00, 0x0D, 0x01, 0x00,
+    0xBD, 0x02, 0x9E, 0x75, 0x14, 0x00, 0x01, 0x00, 0x11, 0x01, 0x01, 0x00, 0x00, 0x0D, 0x01, 0x00,
     0x11, 0x01, 0x01, 0x03, 0x00, 0x20, 0x5F, 0x00, 0x11, 0x01, 0x01, 0x03, 0x00, 0x01, 0x04, 0x02,
     0x0D, 0x04, 0xFF, 0xFF, 0xF3, 0x03, 0x01, 0x04, 0x04, 0x05, 0x06, 0xFF, 0xFF, 0x0F, 0x01, 0x04,
     0x08, 0x0D, 0x0A, 0x12, 0x12, 0x14, 0x7F, 0x7F, 0x24, 0x24, 0x24, 0xFE, 0xFE, 0x28, 0x48, 0x48,

fonts/StackFont.cc

@@ -7,7 +7,7 @@ extern const unsigned char StackFont_sparse_font_data[];
 const unsigned char StackFont_sparse_font_data[36409] FONT_QSPI =
 {
 
-    0xBC, 0x02, 0xB4, 0x9C, 0x02, 0x24, 0x00, 0x01, 0x00, 0x1C, 0x01, 0x01, 0x00, 0x00, 0x0D, 0x01,
+    0xBD, 0x02, 0xB4, 0x9C, 0x02, 0x24, 0x00, 0x01, 0x00, 0x1C, 0x01, 0x01, 0x00, 0x00, 0x0D, 0x01,
     0x00, 0x1C, 0x01, 0x01, 0x06, 0x00, 0x20, 0x5F, 0x00, 0x1C, 0x01, 0x01, 0x06, 0x00, 0x02, 0x05,
     0x03, 0x17, 0x06, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x1F, 0xC0, 0xFF, 0x1F, 0x02, 0x05, 0x08, 0x0A,
     0x0C, 0xE7, 0xE7, 0xE7, 0xE7, 0xE7, 0xE7, 0xE7, 0xE7, 0xE7, 0xE7, 0x01, 0x05, 0x0E, 0x17, 0x10,

src/command.cc

@@ -664,6 +664,17 @@ COMMAND_BODY(LastArg)
 }
 
 
+COMMAND_BODY(LastX)
+// ----------------------------------------------------------------------------
+//   Return the last first argument
+// ----------------------------------------------------------------------------
+{
+    if (!rt.last(0))
+        return ERROR;
+    return OK;
+}
+
+
 COMMAND_BODY(Undo)
 // ----------------------------------------------------------------------------
 //   Return the undo stack

src/command.h

@@ -146,6 +146,7 @@ COMMAND_DECLARE(SystemSetup);   // Select the system menu
 COMMAND_DECLARE(Version);       // Return a version string
 COMMAND_DECLARE(Help);          // Activate online help
 COMMAND_DECLARE(LastArg);       // Return last arguments
+COMMAND_DECLARE(LastX);         // Return last X argument
 COMMAND_DECLARE(Undo);          // Revert to the Undo stack
 COMMAND_DECLARE(ToolsMenu);     // Automatic selection of the right menu
 COMMAND_DECLARE(LastMenu);      // Return to

src/ids.tbl

@@ -280,7 +280,6 @@ CMD(ForStep)
 //
 // ============================================================================
 
-NAMED(LastArg, "LastArguments")
 CMD(Depth)
 NAMED(ToList, "→List")
 CMD(Get)
@@ -547,6 +546,8 @@ CMD(SaveState)
 CMD(SystemSetup)
 CMD(Help)
 CMD(Undo)
+NAMED(LastArg, "LastArguments")
+CMD(LastX)
 
 CMD(Unimplemented)
 

src/menu.cc

@@ -948,7 +948,8 @@ MENU(LastThingsMenu,
 // ----------------------------------------------------------------------------
 //   Menu with the last things
 // ----------------------------------------------------------------------------
-     "Arg",     ID_LastArg,
+     "Args",    ID_LastArg,
+     "X",       ID_LastX,
      "Stack",   ID_Undo,
      "Menu",    ID_LastMenu,
      "Cmd",     ID_Unimplemented);

src/runtime.cc

@@ -978,6 +978,26 @@ bool runtime::last()
 }
 
 
+bool runtime::last(uint index)
+// ----------------------------------------------------------------------------
+//   Push back the last argument on the stack
+// ----------------------------------------------------------------------------
+{
+    size_t nargs = args();
+    if (index >= nargs)
+    {
+        rt.missing_argument_error();
+        return false;
+    }
+    size_t sz = sizeof(object_p);
+    if (available(sz) < sz)
+        return false;
+
+    *--Stack = Args[index];
+    return true;
+}
+
+
 bool runtime::save()
 // ----------------------------------------------------------------------------
 //   Save the stack in the undo area

src/runtime.h

@@ -561,6 +561,11 @@ struct runtime
     //   Push back last arguments
     // ------------------------------------------------------------------------
 
+    bool last(uint index);
+    // ------------------------------------------------------------------------
+    //   Push back last argument
+    // ------------------------------------------------------------------------
+
 
     bool save();
     // ------------------------------------------------------------------------