Skip to Main content Skip to Navigation
New interface
Conference papers

Improving Type Error Messages in OCaml

Arthur Charguéraud 1, 2, * 
* Corresponding author
1 TOCCATA - Formally Verified Programs, Certified Tools and Numerical Computations
LRI - Laboratoire de Recherche en Informatique, Inria Saclay - Ile de France
Abstract : Cryptic type error messages are a major obstacle to learning OCaml or other ML-based languages. In many cases, error messages cannot be interpreted without a sufficiently-precise model of the type inference algorithm. The problem of improving type error messages in ML has received quite a bit of attention over the past two decades, and many different strategies have been considered. The challenge is not only to produce error messages that are both sufficiently concise and systematically useful to the programmer, but also to handle a full-blown programming language and to cope with large-sized programs efficiently. In this work, we present a modification to the traditional ML type inference algorithm implemented in OCaml that, by significantly reducing the left-to-right bias, allows us to report error messages that are more helpful to the programmer. Our algorithm remains fully predictable and continues to produce fairly concise error messages that always help making some progress towards fixing the code. We implemented our approach as a patch to the OCaml compiler in just a few hundred lines of code. We believe that this patch should benefit not just to beginners, but also to experienced programs developing large-scale OCaml programs.
Document type :
Conference papers
Complete list of metadata

Cited literature [21 references]  Display  Hide  Download
Contributor : Arthur Charguéraud Connect in order to contact the contributor
Submitted on : Thursday, December 17, 2015 - 5:01:54 PM
Last modification on : Saturday, June 25, 2022 - 10:18:36 PM
Long-term archiving on: : Saturday, April 29, 2017 - 7:13:22 PM


Files produced by the author(s)



Arthur Charguéraud. Improving Type Error Messages in OCaml. ML Family/OCaml Users and Developers workshops, 2015, Vancouver, Canada. pp.80-97, ⟨10.4204/EPTCS.198.4⟩. ⟨hal-01245843⟩



Record views


Files downloads