Generate fields for markers in REPL so compiler plugin can extract the schema

[koperagen]

without this change plugin cannot see schemas from previous cells, generated by REPL:

val df = DataFrame.read("...")
%%
val df1 = df.add("a") { 42 } 
// only df1.a is available here, because from plugin POV df has empty schema

After this PR generated markers (DataFrame<T>) will have unified structure, so schema can be extracted from both REPL and plugin generated ones

[Jolanrensen]

I don't think we use the word "leaf" for DataFrames. Value/Frame columns are used for this purpose I believe.

[Jolanrensen]

"strictlyEqualValueCols" maybe?

[koperagen]

Yeah, maybe "nested schemas" is a better wording, idk. By leaf here i meant.

interface A {
  val col: Int
  val nested: B <== Leaf
  val nestedFrame: List<B> <== Leaf
}

What do you think?

[Jolanrensen]

so you actually meant "node"? because the schema continues downwards in a different schema? (B is a schema too right?) a "leaf" is normally a node with no children
Yes, then nested schema is better definitely

[zaleslaw]

I see here the gravitation of Graph Theory with presenting dataframe as a tree.
I am fine with both schema - oriented and graph theory oriented wording, but... have a guess that our users closer to the hierarchical schemas wording