Parser accepts malformed types with implicit parameters (#3540) · Issues · Glasgow Haskell Compiler / GHC

Parser accepts malformed types with implicit parameters

The parser in GHC 6.11 currently accepts this:

thing :: (?dude :: Int) -> Int
thing = undefined

Where the type should really be written with => like

thing :: (?dude :: Int) => Int
thing = undefined

Running hlint on the malformed-but-accepted-by-GHC version crashes haskell-src-exts:

benl@humboldt:~$ cat tmp/Main.hs 
main = undefined

thing :: (?dude :: Int) -> Int
thing = undefined

benl@humboldt:~$ hlint tmp/Main.hs 
hlint: src/Language/Haskell/Exts/ParseUtils.hs:(841,18)-(863,53): Non-exhaustive patterns in case

Trac metadata

Trac field	Value
Version	6.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Parser)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

The parser in GHC 6.11 currently accepts this:

```
thing :: (?dude :: Int) -> Int
thing = undefined
```

Where the type should really be written with =\> like

```
thing :: (?dude :: Int) => Int
thing = undefined
```

Running hlint on the malformed-but-accepted-by-GHC version crashes haskell-src-exts:

```
benl@humboldt:~$ cat tmp/Main.hs 
main = undefined

thing :: (?dude :: Int) -> Int
thing = undefined

benl@humboldt:~$ hlint tmp/Main.hs 
hlint: src/Language/Haskell/Exts/ParseUtils.hs:(841,18)-(863,53): Non-exhaustive patterns in case
```

<details><summary>Trac metadata</summary>

| Trac field             | Value             |
| ---------------------- | ----------------- |
| Version                | 6.11              |
| Type                   | Bug               |
| TypeOfFailure          | OtherFailure      |
| Priority               | normal            |
| Resolution             | Unresolved        |
| Component              | Compiler (Parser) |
| Test case              |                   |
| Differential revisions |                   |
| BlockedBy              |                   |
| Related                |                   |
| Blocking               |                   |
| CC                     |                   |
| Operating system       |                   |
| Architecture           |                   |

</details>