MATLAB Transpiler Fix - Output Capture

Problem

MATLAB .m files were not displaying output in the xdl-gui results pane. While the code executed successfully, calls to disp() produced no visible output.

Root Cause

The MATLAB-to-XDL transpiler was converting MATLAB function calls incorrectly:

Before Fix 

disp('Hello');
disp(x);

Was transpiled to:

PRINT ( 'Hello' )
PRINT ( x )

This syntax is invalid in XDL. XDL procedures require comma-separated arguments:

PRINT, 'Hello'
PRINT, x

Solution

Modified xdl-matlab/src/transpiler.rs to detect standalone procedure calls (PRINT, PRINTF) and convert them from MATLAB function syntax func(arg) to XDL procedure syntax PROC, arg.

Changes

In the collect_expression_until_newline() function:

  1. Detection: Check if an identifier is followed by ( and appears at statement start
  2. Special Handling: For PRINT/PRINTF procedures:
    • Insert comma after function name
    • Skip the opening parenthesis
    • Collect arguments with proper function name mapping
    • Skip the closing parenthesis
  3. Function Mapping: Inside PRINT arguments, map MATLAB functions (e.g., log → ALOG)
  4. Result: Proper XDL procedure syntax with correct function names

After Fix 

disp('Hello');
disp(x);

Now correctly transpiles to:

PRINT, 'Hello'
PRINT, x

Complex Case: Nested Functions

The fix also handles nested function calls:

disp(log(10));  % MATLAB

Correctly transpiles to:

PRINT, ALOG(10)  ; XDL with proper function mapping

Without function mapping, log would not be converted to ALOG inside the PRINT arguments, causing a “Function not found” error.

Testing

Created examples/matlab/test_gui_output.m to verify the fix:

disp('Testing GUI output capture');
x = 42;
disp('The answer is:');
disp(x);

CLI Test 

$ xdl examples/matlab/test_gui_output.m
Testing GUI output capture
The answer is:
42

GUI Test

  1. Open xdl-gui
  2. File > Open… > examples/matlab/test_gui_output.m
  3. Click Execute
  4. Output appears in results pane ✓

Impact

  • ✅ All MATLAB disp() calls now work correctly
  • ✅ Output is captured in GUI results pane
  • ✅ CLI output works as expected
  • ✅ All existing MATLAB examples work properly

Files Modified

  • xdl-matlab/src/transpiler.rs - Added special handling for procedure calls
  • Rebuilt xdl-cli and xdl-gui with fixed transpiler

Future Improvements

The same technique can be extended to handle other XDL procedures that may need comma syntax:

  • PLOT
  • Other output procedures
  • User-defined procedures (if added)

Currently, mathematical functions like sin(x) are correctly handled as expressions and don’t need this special treatment.