ucsd-progsys/liquidhaskell

Cannot parse specification

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#1,781 opened on Oct 22, 2020

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good first issue

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Description

{-@ inline id' @-}
id' x = x

{-@ arith :: { id' ( 2 <= 2 ) } @-}
arith = ()

yields:

/home/zgrannan/rewriting-paper/optimization/arith.hs:4:20: error:  Cannot parse specification:
                                                                       unexpected "( "
                                                                       expecting "&&", "->", "<:", "<=>", "==>", "=>", "||", "~>", ':', '}', or monoPredicateP

This is a contrived example but I've run into similar issues generating LH specifications programmatically.

In general I would expect that if the expression {-@ thm : { x } @-} parses, then {-@ thm : { id' (x) } @-} should also parse (excluding the LH builtin operators not already present in Haskell, such as <=>)

Contributor guide

Research direction
Investigate the Liquid Haskell parser source code to understand why the specification fails to parse. Focus on the handling of parentheses in refinement types and trace the error path from `parseSpec`. Look for how function application inside braces is parsed.
Tech stack
None
Domain
backend
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.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
HaskellLiquid Haskell
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60