XDL Array Features Implementation

Summary

Complete implementation of advanced array features for the XDL interpreter, including negative indexing, multi-dimensional arrays (matrices), array element assignment, and array arithmetic operations.

Implemented Features

1. Array Literals

  • Basic array syntax: arr = [1, 2, 3, 4, 5]
  • Empty arrays: empty = []
  • Nested arrays (matrices): matrix = [[1, 2], [3, 4]]

2. Array Indexing

  • Positive indexing: arr[0], arr[2]
  • Negative indexing: arr[-1] (last element), arr[-2] (second to last)
  • Multi-dimensional indexing: matrix[0, 1], matrix[1, 1]
  • Row access: matrix[0] returns entire first row

3. Array Slicing

  • Range slicing: arr[0:3], arr[1:4]
  • Open-ended slicing: arr[2:] (from index to end)
  • Step slicing: arr[0:10:2] (every 2nd element)

4. Array Arithmetic

  • Array-array operations: arr1 + arr2, arr1 - arr2, arr1 * arr2, arr1 / arr2
  • Array-scalar operations: arr * 2, arr + 10, arr mod 7
  • Scalar-array operations: 2 * arr, 10 + arr
  • Modulo operator: 10 mod 3, arr mod 7 (works with scalars and arrays)

5. Array Element Assignment

  • Single element: arr[0] = 100
  • Negative indices: arr[-1] = 999
  • Multi-dimensional: grid[0, 0] = 1, matrix[i, j] = value
  • In loops: Fibonacci, matrix building, array reversal

Architecture Changes

Added NestedArray Type

  • Added XdlValue::NestedArray(Vec<XdlValue>) to support matrices
  • Automatic detection: arrays of arrays become NestedArray
  • Proper string representation for nested structures

Unified Execution Path

  • Removed: Duplicate Executor struct in executor.rs
  • Kept: Single Interpreter struct in lib.rs as the canonical implementation
  • All array operations go through one code path for consistency

Core Implementation Files

  • xdl-core/src/types.rs: Added NestedArray variant to XdlValue
  • xdl-interpreter/src/lib.rs: Main interpreter with array assignment logic
  • xdl-interpreter/src/evaluator.rs: Array evaluation and indexing
  • xdl-parser/: Array parsing (already supported)

Test Coverage

Basic Tests (examples/test_arrays.xdl)

  • Array literals and empty arrays
  • Positive and negative indexing
  • Array slicing
  • Array arithmetic
  • Nested arrays (matrices)
  • Simple element assignment

Advanced Tests (examples/test_advanced_arrays.xdl)

  • Comprehensive negative index testing
  • Multi-dimensional indexing with all combinations
  • Array element assignment in various contexts
  • Combined operations (negative indices in calculations)
  • Array element swapping
  • Matrix diagonal operations
  • Building arrays with assignments (Fibonacci, multiplication tables)
  • Array reversal algorithms
  • Boundary and edge cases

Updated Tests

  • control_flow_tests.xdl: Uses new array features
  • All examples verified to work with current capabilities

Usage Examples 

; Basic array operations
arr = [1, 2, 3, 4, 5]
print, arr[0]          ; 1
print, arr[-1]         ; 5
arr[2] = 99            ; [1, 2, 99, 4, 5]

; Matrix operations
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
print, matrix[1, 1]    ; 5 (center element)
matrix[0, 0] = 100     ; Modify top-left
print, matrix[0]       ; [100, 2, 3] (first row)

; Array building with loops
fib = [0, 1, 0, 0, 0, 0, 0, 0, 0, 0]
for i = 2, 9
  fib[i] = fib[i-1] + fib[i-2]
endfor
; fib = [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

; Matrix building
mult_table = [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
for i = 0, 2
  for j = 0, 2
    mult_table[i, j] = (i + 1) * (j + 1)
  endfor
endfor

Known Limitations

  1. Array slicing with negative indices: Currently arr[-3:-1] returns empty array (needs refinement)
  2. Array creation functions: Functions like fltarr(), intarr() mentioned in old tests may not be fully implemented
  3. Range assignment: arr[0:3] = value not yet supported
  4. System constants: Some math constants like !pi may not be available

Future Enhancements

  1. Implement missing slice edge cases with negative indices
  2. Add array creation functions (fltarr, intarr, etc.)
  3. Support range assignment operations
  4. Add array broadcasting for mismatched dimensions
  5. Implement array methods (min, max, sum, etc.)
  6. Add support for more complex indexing patterns

Testing

Run all array tests:

cargo build --release
./target/release/xdl examples/test_arrays.xdl
./target/release/xdl examples/test_advanced_arrays.xdl

Compliance

  • Code formatted with cargo fmt --all before commit
  • All builds pass without warnings
  • Tests verify functionality end-to-end