CorrectandOptimal: the Regular Expression Inference Challenge

**Abstract.** We propose *regular expression inference (REI)* as a challenge
for code/language modelling, and the wider machine learning community.
REI is a supervised machine learning (ML) and program *optimisation*
task, and poses the problem of finding minimal regular expressions from
examples: Given two finite sets of strings *P* and *N* and a cost function
*cost(.)*, the task is to generate an expression *r* that accepts all
strings in *P* and rejects all strings in *N*, while no other such expression
*r'* exists with *cost(r') < cost(r)*. REI has advantages as a challenge
problem: (i) regular expressions are well-known, widely used, and a natural
idealisation of code; (ii) REI's asymptotic worst-case complexity is well
understood; (iii) REI has a small number of easy to understand parameters
(e.g. *P* or *N* cardinality, string lengths of examples, or the cost
function); this lets us easily finetune REI-hardness; (iv) REI, with its
emphasis on optimisation, is an unsolved problem for deep learning based ML.
Recently, an REI solver was implemented on GPUs, using program synthesis
techniques. This enabled, for the first time, fast generation of minimal
regular expressions for complex REI instances. Building on this advance,
we generate and publish the first large-scale datasets for REI, and
devise and evaluate several initial heuristic and machine learning baselines.
We invite the community to participate and explore ML methods that learn
to solve REI problems. We believe that progress in REI directly translates
to progress in code/language modelling.

**Downloads:** Paper (draft). Challenge site. BibTeX