makeIfAlternate() {
    const context = this.choiceContext;
    const forkContext = this.forkContext;

    /*
     * The head segments are the path of the `if` block.
     * Updates the `true` path with the end of the `if` block.
     */
    context.trueForkContext.clear();
    context.trueForkContext.add(forkContext.head);
    context.processed = true;

    // Creates new path from the `false` case.
    forkContext.replaceHead(context.falseForkContext.makeNext(0, -1));
  }
Makes a code path segment of the `else` block.
@returns {void}