make apply_type error messages more understandable

[vtjnash]

the current apply_type error message assumes the user knows that Type{...} expressions translate into calls to apply_type. This change is intended to make the error messages both more informative (more specific to the error) and more easily comprehended to those uninitiated with the bowels of the julia src code.

[vtjnash]

anyone care to comment on this, or should I just merge it and let people try it out

[JeffBezanson]

I suppose this could be confused with a literal Type{ }.

[vtjnash]

this was actually the hardest one to write for that reason.

[JeffBezanson]

I guess it's ok for now; I can't think of anything better so far.

[JeffBezanson]

It's good for a PR like this to have examples of the old and new output, so it's very quick to judge whether the new output is nicer. Looks OK to me so far.

[vtjnash]

side-comment: did you intend for Tuple types to be constructable with anything (except Vararg) inside?
e.g: Tuple{""}

[vtjnash]

Old:

julia> Vector{""}
ERROR: TypeError: apply_type: in alias, expected Type{T}, got ASCIIString

julia> Union{""}
ERROR: TypeError: apply_type: in parameter of Union, expected Type{T}, got ASCIIString

julia> Array{""}
ERROR: TypeError: apply_type: in Array, expected Type{T}, got ASCIIString

julia> Tuple{Vararg{()}, 1}
ERROR: TypeError: apply_type: in parameter of Tuple, expected Type{T}, got Type{Vararg{()}}

julia> ""{}
ERROR: TypeError: instantiate_type: expected TypeConstructor, got ASCIIString

julia> NTuple{""}
ERROR: TypeError: apply_type: in NTuple, expected Type{T}, got ASCIIString

julia> NTuple{1.2}
ERROR: TypeError: apply_type: in first parameter of NTuple, expected Int64, got Float64

[vtjnash]

New:

julia> Vector{""}
ERROR: TypeError: typealias: in parameter 1, expected Array{T,1}, got ASCIIString

julia> Union{""}
ERROR: TypeError: Union{...} expression: in parameter 1, expected Type, got ASCIIString

julia> Array{""}
ERROR: TypeError: Array: in parameter 1, expected Array, got ASCIIString

julia> Tuple{Vararg{()}, 1}
ERROR: TypeError: Tuple{...} expression: in parameter 1, expected Type, got Type{Vararg{()}}

julia> ""{}
ERROR: TypeError: Type{...} expression: expected Type, got ASCIIString

julia> NTuple{""}
ERROR: TypeError: NTuple: in parameter 1, expected NTuple, got ASCIIString

julia> NTuple{1.2}
ERROR: TypeError: NTuple{T, N} expression: in first parameter of NTuple, expected Int64, got Float64

[ScottPJones]

The error messages for Vector{""} and Array{""} don't seem correct to me, they are not consistent with the error message for Union{""}.
For Array{""}, I would have expected: ERROR: TypeError: Array: in parameter 1, expected Type, got ASCIIString. For Vector, it really would be nice not to confuse people with Array syntax that they didn't use, is there any way the error message could be something like:
ERROR: TypeError: typealias Vector: in parameter 1, expected Type, got ASCIIString?

[vtjnash]

Vector is the name of the variable, and is therefore not part of the expression passed to apply_type. the current template that can be filled in is TypeError: <string>: in <string>, expected <Type>, got <typeof(value)>

[ScottPJones]

But the expected needs to be Type, not Array{Type, 1}

[vtjnash]

The expected is for parameter 1 of Array{T,1} which is T and can be any isbits, Type, or Symbol

[JeffBezanson]

did you intend for Tuple types to be constructable with anything

No, that's a bug.

[JeffBezanson]

I don't think Array: in parameter 1, expected Array is right; it sounds like it expects an Array when it actually expects a Type.

[JeffBezanson]

Improved version of this on the way.

[ScottPJones]

Bug part fixed?