"\n" is displayed weirdly in error messages

Observe:

Prelude> "a\nb" + ()

<interactive>:2:10:
    Couldn't match expected type ‘[Char]’ with actual type ‘()’
    In the second argument of ‘(+)’, namely ‘()’
    In the expression:
      "a\n\
      \b"
      + ()

Moreover, if “\n” is at the end of the string, it simply gets eaten:

Prelude> "a\n" + ()

<interactive>:3:9:
    Couldn't match expected type ‘[Char]’ with actual type ‘()’
    In the second argument of ‘(+)’, namely ‘()’
    In the expression: "a" + ()

It happens in GHC as well as GHCi. Tested on 7.8.3.

Trac metadata

Trac field	Value
Version	7.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 3

added Tbug Trac import labels

The problem with a newline at the end of a string was fixed in #9681 (closed), slated for GHC 7.10.1. Let's leave this issue open for the formatting issue.

Trac metadata

Trac field	Value
Related	→ #9681 (closed)

added newcomer label

assigned to @trac-jlengyel

unassigned @trac-jlengyel

The formatting is intentional, see #4436 (closed). It would be nice to use the original syntax, though (and set the "original syntax" of a quasiquoter to use the multiline thing).

@Artyom.Kazak: what exactly do you find weird about the current error message? The printing over multiple lines, or just the extra slashes that are added. Perhaps the following would be an improvement:

In the expression:
      "a\n
      b"
      + ()

Replying to [ticket:9392#comment:95558 rwbarton]:

The formatting is intentional, see #4436 (closed). It would be nice to use the original syntax, though (and set the "original syntax" of a quasiquoter to use the multiline thing).

To show the exception from #4436 (closed), the following code path is used:

TcSplice.runMeta -> Outputable.ppr -> (instance Outputable HsLit) -> Outputable.pprHsString -> GHC.Show.showMultiLineString

I don't see an easy way to make the change you propose.

Trac metadata

Trac field	Value
Type	Bug → FeatureRequest

added Tfeature request label and removed Tbug newcomer labels

added Tbug label

added Plow label