B-Lang-org/bsc

Better error message for -> instead of => in type signature

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#337 opened on Mar 19, 2021

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 (3 comments) (0 reactions) (0 assignees)Haskell (1,108 stars) (178 forks)batch import
good first issue

Description

We've seen all sorts of hilarity including things like:

Type error at: d

Expected type: t

Inferred type: (Prelude.IsModule m mType, Prelude.Bits t st) (ironically one of the easier-to-diagnose variants).

I suspect some sort of up-front check that classes aren't where they aren't supposed to be in a type signature would help here. Add comment

Contributor guide

Tech stack
None
Domain
developer experiencetooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Understanding of parsing type signaturesFamiliarity with compiler error messages
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Focus on the parser source files for type signatures, likely in Parsers or ParserUtils. Identify where the error message is generated and add an upfront check for misplaced class constraints. Review the three comments on the issue for additional hints.