markAsRead(segments, variable) {
		for (const segment of segments) {
			const info = this.info.get(segment);

			if (info) {
				info.freshReadVariables.add(variable);

				// If a variable is freshly read again, then it's no more out-dated.
				info.outdatedReadVariables.delete(variable);
			}
		}
	}
Mark a given variable as read on given segments.
@param {PathSegment[]} segments The segments that it read the variable on.
@param {Variable} variable The variable to be read.
@returns {void}