internal
fun CharSequence.lineAndColumnFromRange(range: IntRange): Pair<Int, Int> {
    require(range.endInclusive <= lastIndex)
    return lineAndColumnFor(range.start)
}


/**
 * Computes the 1-based line and column numbers for the given [index].
 */
internal
fun CharSequence.lineAndColumnFor(index: Int): Pair<Int, Int> {
    val prefix = take(index)
    val lineCountBefore = prefix.count { it == '\n' }

        preserve(*ranges.toTypedArray())

    fun subText(range: IntRange): ProgramText =
        ProgramText(text.substring(range))

    internal
    fun lineNumberOf(index: Int): Int =
        text.lineAndColumnFor(index).first

    private
    fun complementOf(ranges: Array<out IntRange>): ArrayList<IntRange> {
        require(ranges.isNotEmpty())

        val sortedRanges = ranges.sortedBy { it.first }