add an API to declare the standard "prelude" types to a schema type system

[mvdan]

See #207 (comment).

[mvdan]

Bonus points if this also makes initializing a typesystem easier. Right now it's:

ts := schema.TypeSystem{}
ts.Init()
// accumulate all basic types

Would be nice if it was instead just something like:

ts := schema.StandardTypeSystem() // already includes basic types

[mvdan]

The new func MustTypeSystem(types ...Type) *TypeSystem in master seems close to this; imagine if I could do:

ts := schema.MustTypeSystem(schema.Prelude...)

I'd slightly prefer just schema.StandardTypeSystem() though, since it would be clearer it should never error/panic, and it's also more descriptive without the schema. package repetition.

[mvdan]

FYI @warpfork ^ since you did #232

[warpfork]

Yeah, we should have something for this.

I didn't form strong opinions on how exactly it should be written (because I still sort of wish we could get away from these golang constructors at all, but, here we are for a while yet, it seems).

A list of prelude types that one can unroll into the varargs for MustTypeSystem would seem good, I guess, if we can get away with something that light.

Or, I've also now a couple of times had the wish for a constructor method for TypeSystem that takes both an existing TypeSystem and a list of new types and just adds them together to form a new one. (This mostly has come up in tests, and I'm not sure the desire is very correct, on second thought. Just a thought.)

[mvdan]

dmt.Compile now spawns the full prelude:

go-ipld-prime/schema/dmt/compile.go

Lines 15 to 33 in ac5b5fd

	// Prelude; probably belongs elsewhere.
	{
	ts.Accumulate(schema.SpawnBool("Bool"))
	ts.Accumulate(schema.SpawnInt("Int"))
	ts.Accumulate(schema.SpawnFloat("Float"))
	ts.Accumulate(schema.SpawnString("String"))
	ts.Accumulate(schema.SpawnBytes("Bytes"))
	ts.Accumulate(schema.SpawnAny("Any"))
	ts.Accumulate(schema.SpawnMap("Map", "String", "Any", false))
	ts.Accumulate(schema.SpawnList("List", "Any", false))
	// Should be &Any, really.
	ts.Accumulate(schema.SpawnLink("Link"))
	// TODO: schema package lacks support?
	// ts.Accumulate(schema.SpawnUnit("Null", NullRepr))
	}

And I think we're in agreement that the vast majority of users should use schemas by using ipld.LoadSchema and the DSL rather than manually spawning and accumulating types.

For that reason, I think we can close this issue. Note that the prelude doesn't include Null right now; that's blocked on support for unit typekinds, so I've raised #336 as a reminder.