Newbie help features

Often a newbie comes to #haskell and asks why something doesn't work in ghci. There are at least two cases:

"why doesn't type Bar = (Char, Int) work"?

and

"why doesn't f = 1 work?" (that is function definitions)

It wouldn't be much work to recognize these cases and then give the user some hints on putting those definitions into a file, etc.

Another case where error messages can be improved is the following:

type Foo = (char, int) -- the intention is clear, but the error message might not be clear to a new user. Suggestion: when the parsed type variables are the same modulo case to an existing core type(Int, Bool, Array, etc) and Foo doesn't take those type parameters, tell the user he needs to use proper casing.

Trac metadata

Trac field	Value
Version	6.6.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	GHCi
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown

mentioned in issue #1387 (closed)

changed weight to 3

added GHCi Tfeature request Trac import labels

Good ideas!

Trac metadata

Trac field	Value
Architecture	Unknown → Unknown/Multiple

Trac metadata

Trac field	Value
Operating system	Unknown → Unknown/Multiple

type Bar = (Char, Int) works now in GHCi.

f = 1 doesn’t, but given that GHCi supports all(?) other toplevel declarations by now, I wonder why. I could even print something helpful like

> f = 1
Defined: f :: Num a => a

or less verbose

> f = 1
f :: Num a => a

so that the user knows what’s going on. Or simply treat it exactly like let f = 1.

Trac metadata

Trac field	Value
TypeOfFailure	- → OtherFailure

mentioned in issue #9177 (closed)

Split the last suggestion in the original ticket to #9177 (closed)

Support for top-level declarations was added in #4929 (closed).

With 1ff7f09b, f = 1 now prints:

+    parse error on input ‘=’
+    Perhaps you need a 'let' in a 'do' block?
+    e.g. 'let x = 5' instead of 'x = 5'

Trac metadata

Trac field	Value
Related	→ #4929 (closed)

closed

"why doesn't f = 1 work?" (that is function definitions)

This is the only part remaining for this ticket, and already tracked as #7253 (closed).

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed
Related	#4929 (closed) → #4929 (closed), #7253 (closed), #9177 (closed)

added Plow label