ucsd-progsys/liquidhaskell

Document that specs can depend on arguments of enclosing functions

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#2,442 opened on Nov 19, 2024

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Description

Today I learned that the meaning of specs of local bindings can depend on arguments of an enclosing function. For instance, in the following function from the test suite, arg0 is available to the spec of bar.

{-@ foo :: x:_ -> y:_ -> {v:Int | v = x + y} @-}
foo :: Int -> Int -> Int
foo arg0 = bar
  where
    {-@ bar :: x:_ -> {v:Int | v = x + arg0} @-}
    bar arg1 = arg0 + arg1

It doesn't work for other things than arguments though, e.g. z is not in scope in the following spec.

{-@ foo :: x:_ -> y:_ -> {v:Int | v = x + y} @-}
foo :: Int -> Int -> Int
foo arg0 = bar
  where
    z = arg0
    {-@ bar :: x:_ -> {v:Int | v = x + z} @-}
    bar arg1 = arg0 + arg1

We should document the fact that arguments of enclosing functions are in scope. This is also true for other local bindings. See the comments below.

Contributor guide

Research direction
Document that Liquid Haskell specs in local bindings can reference arguments of enclosing functions, but not other local bindings (unless they are in scope through other mechanisms). Add examples and clarification to the existing documentation.
Tech stack
haskell
Domain
backendtoolingdocumentation
Issue type
Documentation
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
1
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Under 1 hour
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Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Haskell
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
90