Function captureWildcard

src/compute-engine/boxed-expression/match.ts:76–101

* Return a new substitution based on arg. `substitution`, but with wildcard (of value *expr*) * added. * Returns given *substitution* unchanged if wildcard is a unnamed, or is already present in * substitution. * * Returns `null` in cases either of attempting to an existing wildcard/substitutio

(
  wildcard: string,
  expr: Expression,
  substitution: BoxedSubstitution
)

/**
 * Return a new substitution based on arg. `substitution`, but with wildcard (of value *expr*)
 * added.
 * Returns given *substitution* unchanged if wildcard is a unnamed, or is already present in
 * substitution.
 *
 * Returns `null` in cases either of attempting to an existing wildcard/substitution with a
 * different value, or if the given *expr* is, or contains, a wildcard expression.
 *
 * @param wildcard
 * @param expr
 * @param substitution
 * @returns
 */
function captureWildcard(
  wildcard: string,
  expr: Expression,
  substitution: BoxedSubstitution
): BoxedSubstitution | null {
  console.assert(wildcard.startsWith('_'));

  // If this is a universal wildcard, it always matches and no need to add it
  // to the substitution record.
  if (wildcard === '_' || wildcard === '__' || wildcard === '___')
    return substitution;

  if (wildcard in substitution) {
    // There was already a matching wildcard, make sure this one is identical.
    // Patterns are syntax: a capture can contain pattern-side artifacts (a
    // pre-bound wildcard like the unknown `_x` during equation solving, raw