Use type alias when you want an abbreviation for a long type name. If you
don't want to write List (Dict String SomeVal) over and over again, you can
make a type alias to shorten it.
Use a type alias to give a name to record types, and this also gives you a
nice shorthand constructor. If you do
type alias P2D = {x : Float, y : Float}
then you can do
P2D 0.0 1.0
as equivalent to
{x = 0.0, y = 1.0}
and it saves you the effort of writing the literal record type over and
over again.
Use a type when you want to create a new type, that's distinct in the
compiler. So if you want to distinguish FileName from String, you can make
a type, and this will ensure that you have to tag any strings with FileName
to use them where a FileName is expected.
And, if you want to define constructors and variants for your type (i.e. a
tagged union), or do anything with recursive types, use type, since type
alias doesn't allow this.
Why not use *type* everywhere?
>
Because then you would have to pattern match every time you used an alias
for something, and if you don't want the two types to be distinct in the
compiler, then that's a lot of overhead with no benefit.
On Sun, Dec 18, 2016 at 3:57 PM, Richard Haven <
richardha...@santacruzsoftware.com> wrote:
> When should one use *type *and when should one use *type alias*? Why not
> use *type* everywhere?
>
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