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ICFP 2018
Sun 23 - Sat 29 September 2018 St. Louis, Missouri, United States
Mon 24 Sep 2018 11:15 - 11:37 at Stifel Theatre - Environments and Tools Chair(s): Alejandro Russo

We report on the experience of developing Merlin, a language server for the OCaml programming language in development since 2013. Merlin is a daemon that connects to your favourite text editor and provides services that require a fine-grained understanding of the programming language syntax and static semantics: instant feedback on warnings and errors, autocompletion, type of the code under the cursor'',go to definition'', etc.

Language servers need to handle incomplete and partially-incorrect programs, and try to be incremental to minimize recomputation after small editing actions. Merlin was built by carefully adapting the existing tools (the OCamllex lexer and Menhir parser generators) to better support incrementality, incompleteness and error handling. These extensions are elegant and general, as demonstrated by the interesting, unplanned uses that the OCaml community found for them. They could be adapted to other parsing tools – in any programming language.

Besides incrementality, we discuss the way Merlin communicates with editors, describe the design decisions that went into some demanding features and report on some of the non-apparent difficulties in building good editor support, emerging from expressive programming languages or frustrating tooling ecosystems.

We expect this experience report to be of interest to authors of interactive language tooling for any programming language; many design choices may be reused, and some hard-won lessons can serve as warnings.

Mon 24 Sep
Times are displayed in time zone: (GMT-05:00) Guadalajara, Mexico City, Monterrey change

10:30 - 12:00: Research Papers - Environments and Tools at Stifel Theatre
Chair(s): Alejandro RussoChalmers University of Technology, Sweden
icfp-2018-papers10:30 - 10:52
Andrey MokhovNewcastle University, UK, Neil Mitchell, Simon Peyton JonesMicrosoft, UK
icfp-2018-papers10:52 - 11:15
Kenneth Foner, Hengchu ZhangUniversity of Pennsylvania, Leonidas LampropoulosUniversity of Pennsylvania
icfp-2018-papers11:15 - 11:37
Frédéric BourFacebook Paris, Thomas Réfis, Gabriel SchererINRIA Saclay
icfp-2018-papers11:37 - 12:00
Chandrakana NandiUniversity of Washington, USA, James R. WilcoxUniversity of Washington, Taylor BlauUniversity of Washington, Dan GrossmanUniversity of Washington, Zachary TatlockUniversity of Washington, Seattle