FINDGEN Function Update

Overview

Updated FINDGEN (and DINDGEN) to support the full IDL/GDL function signature with multiple dimensions.

Function Signature 

Result = FINDGEN(D1 [, D2, ..., D8] [, INCREMENT=value] [, START=value])

Changes Made

1. Multi-Dimensional Support

  • Before: FINDGEN only accepted a single dimension argument
  • After: FINDGEN now accepts 1-8 dimension arguments

2. Return Type

  • 1D arrays: Returns XdlValue::Array (backward compatible)
  • Multi-dimensional arrays: Returns XdlValue::MultiDimArray with shape metadata

3. Implementation Details

Location

  • File: xdl-stdlib/src/math.rs
  • Functions updated: findgen(), dindgen()

Key Features

  • Validates all dimensions are non-negative
  • Calculates total size as product of all dimensions
  • Generates sequential values starting from 0.0 with increment 1.0
  • Preserves shape information for multi-dimensional arrays

4. Examples 

; 1D array (backward compatible)
arr1 = FINDGEN(5)
; Returns: [0.0, 1.0, 2.0, 3.0, 4.0]

; 2D array (3 rows × 4 columns)
arr2 = FINDGEN(3, 4)
; Returns: 3×4 array with values 0-11

; 3D array (2×3×2)
arr3 = FINDGEN(2, 3, 2)
; Returns: 2×3×2 array with values 0-11

; Works with math operations
arr4 = FINDGEN(2, 2) * 2
; Returns: 2×2 array with values [0, 2, 4, 6]

5. Testing

  • Created test script: test_findgen_simple.xdl
  • Verified backward compatibility with existing code
  • Tested multi-dimensional array generation
  • Confirmed math operations work with multi-dimensional arrays

Future Enhancements

Keyword Arguments (TODO)

The INCREMENT and START keywords are documented but not yet implemented because the XDL evaluator doesn’t fully support keyword arguments for functions.

Planned support:

; Start at 10, increment by 2
arr = FINDGEN(5, START=10, INCREMENT=2)
; Should return: [10.0, 12.0, 14.0, 16.0, 18.0]

Implementation note: When the evaluator adds keyword support for functions (currently only available for procedures via call_procedure_with_keywords), update the findgen() function to extract START and INCREMENT from keywords parameter.

Required Evaluator Changes

Currently in xdl-interpreter/src/evaluator.rs (lines 62-65):

// TODO: Handle keywords
if !keywords.is_empty() {
    return Err(XdlError::NotImplemented("Function keywords".to_string()));
}

Once this is implemented, the findgen() function can be enhanced to accept keyword arguments.

Compatibility

IDL/GDL Compatibility

  • ✅ Multiple dimensions (D1-D8)
  • ✅ Array generation with sequential values
  • ✅ MultiDimArray shape preservation
  • ⏳ START keyword (pending evaluator support)
  • ⏳ INCREMENT keyword (pending evaluator support)

Backward Compatibility

  • ✅ All existing single-dimension FINDGEN calls work unchanged
  • ✅ Return type for 1D arrays remains XdlValue::Array
  • ✅ No breaking changes to existing code

Files Modified

  1. xdl-stdlib/src/math.rs
    • Updated findgen() function (lines 367-458)
    • Updated dindgen() documentation (lines 460-472)

Build Status

✅ All compilation successful ✅ Tests passing ✅ Existing examples working correctly