Given a table type and a function, returns the AST for the foldable function as JSON

FoldedRowExpression.pq

(tableType as type, fn as function) =>
let
    TransformNode = (x) => Record.FromList(List.Transform(Record.FieldValues(x), TransformValue), Record.FieldNames(x)),
    TransformValue = (x) => if x is record then TransformRecord(x) else if x is list then TransformList(x) else x,
    TransformList = (x) => List.Transform(x, TransformValue),
    TransformRecord = (x) => 
        if x = RowExpression.Row then [Kind="Row"]
        else if x[Kind] = "Constant" then TransformConstant(x)
        else TransformNode(x),
    TransformConstant = (x) => if x[Value] is function and TryFunctionName(x[Value]) <> null then [Kind="Identifier", Name=TryFunctionName(x[Value])]
        else if x[Value] is function then [Kind="Constant", Value="<function>", Type=TextType(Value.Type(x[Value]))]
        else x & [Type=TextType(Value.Type(x[Value]))],
    TryFunctionName =
        let
            Shared = Table.TransformColumns(Record.ToTable(#sections), {{"Value", Record.FieldNames}})[Value]{0},
            Shared2 = List.RemoveItems(Record.FieldNames(#shared), Shared),
            Library = Record.SelectFields(#shared, Shared2),
            Functions = Table.Buffer(Table.SelectRows(Record.ToTable(Library), each try ([Value] is function) otherwise false))
        in
            (fn) => Table.First(Table.SelectRows(Functions, each [Value] = fn))[Name]?,
    TextType = (t as type) as text => 
        let
            nonNullableType = Type.NonNullable(t),
            TypeDescription = if Type.Is(nonNullableType, type binary) then "binary"
            else if Type.Is(nonNullableType, type date) then "date"
            else if Type.Is(nonNullableType, type datetime) then "datetime"
            else if Type.Is(nonNullableType, type datetimezone) then "datetimezone"
            else if Type.Is(nonNullableType, type duration) then "duration"
            else if Type.Is(nonNullableType, type function) then "function"
            else if Type.Is(nonNullableType, type list) then "list"
            else if Type.Is(nonNullableType, type logical) then "logical"
            else if Type.Is(nonNullableType, type none) then "none"
            else if Type.Is(nonNullableType, type null) then "null"
            else if Type.Is(nonNullableType, type number) then "number"
            else if Type.Is(nonNullableType, type record) then "record"
            else if Type.Is(nonNullableType, type table) then "table"
            else if Type.Is(nonNullableType, type text) then "text"
            else if Type.Is(nonNullableType, type time) then "time"
            else if Type.Is(nonNullableType, type type) then "type"
            else if Type.Is(nonNullableType, type action) then "action"
            else if Type.Is(type anynonnull, nonNullableType) then "any"
            else error "Unknown type",
            TypeString = if TypeDescription = "any" then 
                             if Type.IsNullable(t) then 
                                 "any" else "anynonnull"
                             else if Type.IsNullable(t) then 
                                 "nullable " & TypeDescription 
                             else TypeDescription
        in
            TypeString,
    MakeAst = (fn) => Text.FromBinary(Json.FromValue(TransformRecord(RowExpression.From(fn)))),
    table = #table(tableType, {}),
    ConstantFolding =
        Table.AddColumn(
            Table.View(table, [
                OnAddColumns = (c) => Table.FromRows(
                    {List.Repeat({null}, Table.ColumnCount(table)) & {MakeAst(c{0}[Function])}},
                    Table.ColumnNames(table) & {"____"})]),
        "____",
        fn){0}[____]
in
    ConstantFolding