Lean 4 fork for HoTT-compatible kernel extensions (Path types, transport, HITs). Maintained against upstream leanprover/lean4.
3a309ba4eb
This PR improves the error message encountered in the case of a type class instance resolution failure, and adds an error explanation that discusses the common new-user case of binary operation overloading and points to the `trace.Meta.synthInstance` option for advanced debugging. ## Example ```lean4 def f (x : String) := x + x ``` Before: ``` failed to synthesize HAdd String String ?m.5 Hint: Additional diagnostic information may be available using the `set_option diagnostics true` command. ``` After: ``` failed to synthesize instance of type class HAdd String String ?m.5 Hint: Type class instance resolution failures can be inspected with the `set_option trace.Meta.synthInstance true` command. Error code: lean.failedToSynthesizeTypeclassInstance [View explanation](https://lean-lang.org/doc/reference/latest/find/?domain=Manual.errorExplanation&name=lean.failedToSynthesizeTypeclassInstance) ``` The error message is changed in three important ways: * Explains *what* failed to synthesize, using the "type class" terminology that's more likely to be recognized than the "instance" terminology * Points to the `trace.Meta.synthInstance` option which is otherwise nearly undiscoverable but is quite powerful (see also leanprover/reference-manual#663 which is adding commentary on this option) * Gives an error explanation link (which won't actually work until the next release after this is merged) which prioritizes the common-case explanation of using the wrong binary operation |
||
|---|---|---|
| .claude | ||
| .github | ||
| doc | ||
| images | ||
| releases_drafts | ||
| script | ||
| src | ||
| stage0 | ||
| tests | ||
| .gitattributes | ||
| .gitignore | ||
| .gitpod.Dockerfile | ||
| .gitpod.yml | ||
| .ignore | ||
| CMakeLists.txt | ||
| CMakePresets.json | ||
| CODEOWNERS | ||
| CONTRIBUTING.md | ||
| flake.lock | ||
| flake.nix | ||
| lean-toolchain | ||
| lean.code-workspace | ||
| LICENSE | ||
| LICENSES | ||
| README.md | ||
| RELEASES.md | ||
This is the repository for Lean 4.
About
- Quickstart
- Homepage
- Theorem Proving Tutorial
- Functional Programming in Lean
- Documentation Overview
- Language Reference
- Release notes starting at v4.0.0-m3
- Examples
- External Contribution Guidelines
Installation
See Install Lean.
Contributing
Please read our Contribution Guidelines first.
Building from Source
See Building Lean.