The text "Possible fix: add an instance declaration for ..." is redundant and not usually helpful
The current state of affairs: Given a typical type error, for example
"a" + "b"we get
No instance for (Num [Char])
arising from a use of `+'
Possible fix: add an instance declaration for (Num [Char])
In the expression: "a" + "b"
In an equation for `it': it = "a" + "b"I'm concerned with the third line here:
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It is redundant, for it just repeats information from the first line. In my experience, the redundancy sometimes hinders usability, namely, when the types get very long, visually burying the problematic expression.
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Furthermore it is often misleading: Everyday type errors stem from incorrect usage of a library, not from missing bits of a library. The line tends to be confusing especially for new users: the only ones who might have profited from the redundancy.
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To expand a bit on (1): An imported bit of information in the type error is the fact that the type mismatch lies in the application of (+) to "a". The user gains this information by combination of lines 2 and 4. It is incovenient that line 3 visually seperates those lines.
I propose that the problematic line be simply removed.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.4.2 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |