7. A computer program product for evaluating a regular expression in computing, said computer program product comprising: a non-transitory computer readable storage medium having computer readable program code embodied therewith, the computer readable program code comprising: computer readable program code configured to receive text strings; computer readable program code configured to generate, using the received text strings and a list of regular expression meta-characters, a data structure containing a plurality of grams with positional information identifying a location of each of the plurality of grams within the received text strings, wherein the grams are of a certain character length based upon an input gram length; computer readable program code configured to receive a query comprising a regular expression, wherein the regular expression comprises a pattern for recognizing at least one text string from among the received text strings; computer readable program code configured to convert the regular expression into a gram-constrained parse tree comprising nodes comprising character classes and nodes comprising a gram having a character length equal to the input gram length; computer readable program code configured to generate a positional index query based on the gram-constrained parse tree; and computer readable program code configured to identify a subset of the text strings comprising at least one match for the query, wherein to identify comprises filtering the data structure by executing the positional index query on the data structure to generate a list of candidate text strings and filtering the list of candidate text strings against the regular expression to generate the subset of text strings.
10. The computer program product according to claim 7 , wherein said computer readable program code is configured to filter the list of candidate text strings via post-processing, the post-processing being governed by a level of detail returned within optional response metadata generated with the list of candidate text strings.