leanprover / leanprover/fp-lean
Provide example error messages that might result from unintended auto-implicits
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- Dominant language
- Lean
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Description
Auto-implicits can lead to confusing error messages, so the book should discuss them.
An example that occurred recently on Zulip:
structure RectangularPrism where
height: Float
width: Float
depth: float
deriving Repr
gave the message
typeclass instance problem is stuck, it is often due to metavariables
Repr (?m.53213 x✝ prec✝)
Ideally, there'd be a few examples of this with various language features, as these messages are truly inscrutable.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by locating the book section that discusses auto-implicits and review the linked Zulip example. The documentation is done when it includes several representative examples of confusing error messages from unintended auto-implicits and explains their likely cause.
Written by the indexing model from the issue text.
Assessment
- Domain
- documentation
- Issue type
- Documentation
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100