Typed and unambiguous pattern matching on strings using regular expressions

Abstract

We show how to achieve typed and unambiguous declarative pattern matching on strings using regular expressions extended with a simple recording operator.We give a characterization of ambiguity of regular expressions that leads to a sound and complete static analysis. The analysis is capable of pinpointing all ambiguities in terms of the structure of the regular expression and report shortest ambiguous strings. We also show how pattern matching can be integrated into statically typed programming languages for deconstructing strings and reproducing typed and structured values.We validate our approach by giving a full implementation of the approach presented in this paper. The resulting tool, reg-exp-rec, adds typed and unambiguous pattern matching to Java in a stand-alone and non-intrusive manner. We evaluate the approach using several realistic examples.

Translating regular expression matching into transducers

“…2 To develop the deterministic parser that corresponds to the nondeterministic parser of the above definition, we first introduce a nondeterministic parser N JrK that consumes at least one letter. It can be recursively defined by using N JrK as follows:…”

“…Kw, the proof is basically a straightforward extension of Theorem 2. 2 The behaviour of problematic regular expressions are not described in the manuals of these languages as far as we know. We checked the behaviour by executing matching of several problematic regular expressions in these languages.…”

“…if w = w then unit w else DJr * 1 K r c w = Some w , ρ (2) ρ = ρ ρ (3) We only show the case where w ∈ L(r c ). The other case is proved in a similar manner.…”

WebSelF: A Web Scraping Framework

“…We have therefore created a concrete implementation of the framework in Java to test this hypothesis. The implementation includes selection functions using regular expressions [1], XPath expressions, and it includes a full browser in order to let client-side computation take place and provide presentational information about the given web page. Furthermore automatic reinduction of validation functions and composition of validation functions as described in Sect.…”

Bit-coded Regular Expression Parsing

“…Parse trees for regular expressions can be formalized as ad-hoc data structures [6,2], representing exactly how the string can be expressed in the regular expression. This means that both membership testing, substring groups and regular expression types can be found by filtering away the extra information in the parse tree.…”