Put "Error:" before error output

[Konstantine Rybnikov]

Yes, correct. But I think ghci's errors are already distinguishable from
`error`, e.g. this:

```
Prelude> :set -Wall
Prelude> :load test
[1 of 1] Compiling Main             ( test.hs, interpreted )

test.hs:1:1: Warning:
    Top-level binding with no type signature: main :: IO ()
Ok, modules loaded: Main.
Prelude> let main = asdasdasd
<interactive>:6:12: Not in scope: ‘asdasdasd’
*Main> :load test2
[1 of 1] Compiling Main             ( test2.hs, interpreted )

test2.hs:1:8: Not in scope: ‘foo’
Failed, modules loaded: none.
Prelude> error "foo"
*** Exception: foo
```

will change to:

```
Prelude> :set -Wall
Prelude> :load test
[1 of 1] Compiling Main             ( test.hs, interpreted )

test.hs:1:1: Warning:
    Top-level binding with no type signature: main :: IO ()
Ok, modules loaded: Main.
Prelude> let main = asdasdasd
<interactive>:6:12: Not in scope: ‘asdasdasd’
*Main> :load test2
[1 of 1] Compiling Main             ( test2.hs, interpreted )

test2.hs:1:8: Error: Not in scope: ‘foo’
Failed, modules loaded: none.
Prelude> error "foo"
*** Exception: foo
```

Don't think this will cause any trouble (well, except for current tests
that check for output, which was mentioned in ticket #10021, but I hope
it's not that big of a problem).


On Tue, Jan 27, 2015 at 7:05 PM, Brandon Allbery <allbery.b at gmail.com>
wrote:

> On Tue, Jan 27, 2015 at 12:02 PM, Konstantine Rybnikov <k-bx at k-bx.com>
> wrote:
>
>> Sorry, I didn't get what you mean. Do you mean `error` [0] function from
>> Prelude? The discussion is currently not regarding runtime program
>> behavior, nor it is about `error` function. It's rather regarding compiler
>> output message on compilation failure, so it shouldn't get mixed with your
>> program's runtime behavior in any way
>
>
> ...unless using runhaskell/runghc.
>
> --
> brandon s allbery kf8nh                               sine nomine
> associates
> allbery.b at gmail.com
> ballbery at sinenomine.net
> unix, openafs, kerberos, infrastructure, xmonad
> http://sinenomine.net
>
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