Function getExpressionDimension

src/compute-engine/numerics/unit-data.ts:420–456

(
  expr: UnitExpression
)

  const siValue = (value + fromOffset) * from.scale;
  return siValue / to.scale - toOffset;
}

// ---------------------------------------------------------------------------
// Compound unit expressions
// ---------------------------------------------------------------------------

/**
 * A MathJSON-like unit expression: either a string (simple unit symbol) or
 * an array like `["Divide", "m", "s"]`.
 */
export type UnitExpression = string | [string, ...any[]];

/**
 * Compute the dimension vector for a MathJSON unit expression.
 *
 * - If `expr` is a string, delegates to `getUnitDimension`.
 * - `["Multiply", a, b, ...]` — adds dimension vectors component-wise.
 * - `["Divide", a, b]` — subtracts b's dimension from a's.
 * - `["Power", base, exp]` — multiplies base dimension by exp.
 *
 * Returns `null` if any component is unrecognised.
 */
export function getExpressionDimension(
  expr: UnitExpression
): DimensionVector | null {
  if (typeof expr === 'string') return getUnitDimension(expr);

  if (!Array.isArray(expr) || expr.length < 2) return null;

  const op = expr[0];

  if (op === 'Multiply') {
    const result: DimensionVector = [0, 0, 0, 0, 0, 0, 0, 0];
    for (let i = 1; i < expr.length; i++) {
      const d = getExpressionDimension(expr[i]);
      if (!d) return null;
      for (let j = 0; j < 8; j++) result[j] += d[j];
    }
    return result;
  }