Skip to content

[JsLIGO] Allow parenthesised type expressions as summands of sum types ("discriminated union")

Christian Rinderknecht requested to merge rinderknecht@sum_type_expr into dev

Motivation and Context

For testing the new sum types, it is useful for the concrete syntax to allow parentheses of summands.

type t = {a: "A"} | ({b: "B"} | {c: "C"}); 


In fact, the MR allows general union types in the front-end:

type t = int | ["A"] | ["B", string]

and the rest of the pipeline will filter some.

In fact, the parser does not produce T_Sum nodes directly. Instead, the semantic actions of the new union types filters the unions that could be interpreted as sum types and produce those nodes. This is of course a hack, and, in the future, the node T_Sum should be removed entirely.

One incompatibility is now the case

type t = ["A",int] 

which is parsed now as an array type instead of a sum type. For a sum type, the variant needs to be introduced by a vertical bar, like so:

type t = | ["A", int]


  • compiler
  • website
  • webide
  • vscode-plugin
  • debugger

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to not work as expected)
  • Performance improvement (non-breaking change that improves performance)
  • None (change with no changelog)



  • If a new syntax has been introduced, put a message on slack ligo-lsp
  • Changes follow the existing coding style (use dune @fmt to check).
  • Tests for the changes have been added (for bug fixes / feature).
  • Documentation has been updated.
  • Changelog description has been added (if appropriate).
  • Start titles under ## Changelog section with #### (if appropriate).
  • There is no image or uploaded file in changelog
  • Examples in changed behaviour have been added to the changelog (for breaking change / feature).
Edited by Christian Rinderknecht

Merge request reports