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Monomorphisation: add commutation with `let`

E. Rivas requested to merge er433/monomorphisation/commute into dev

Motivation and Context

It was reported by Heitor that tools/debugger/ligo-debugger/test/contracts/tezos-types.mligo doesn't work with compile contract:

$ ligo compile contract tools/debugger/ligo-debugger/test/contracts/tezos-types.mligo
File "tools/debugger/ligo-debugger/test/contracts/tezos-types.mligo", line 1, characters 34-59:
  1 | let empty () : 42 sapling_state = Tezos.sapling_empty_state
  2 | 

Cannot monomorphise the expression.

There were some changes on how let foo () = ... compiles (expansion, pattern matching).


In this MR we extend our monomorphisation pass with an internal pass that commutes (let x = t in u)@{T} into let x = t in (u@{T}).


  • 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 E. Rivas

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