This repository contains a proof of concept on decompiling Power Query (M) functions.

AST.pq - a deep call to Value.ResourceExpression in order to demo how the Abstract Syntax Tree (AST) looks for List.Range

=Value.ResourceExpression(List.Range)
    [Expression]
        [Arguments]{0}
            [Function]
                [Expression]
                    [Expression]

AST2json.pq - serializing the output from Value.ResourceExpression to JSON

Decompile.pq - function definition that translates an AST into an expression

Expression.pq - same code as Decompile(x) function exposed as an expression(query)

The query that would return the list of functions that should deompile is:

= List.Select(Record.FieldNames(#shared),each Value.ResourceExpression(Record.Field(#shared,_))[Kind]="Function")

Which brings up this output:

Date.DayOfWeekName , Date.IsInCurrentDay , Date.IsInCurrentMonth , Date.IsInCurrentQuarter , Date.IsInCurrentWeek , Date.IsInCurrentYear , Date.IsInNextDay , Date.IsInNextMonth , Date.IsInNextNDays , Date.IsInNextNMonths , Date.IsInNextNQuarters , Date.IsInNextNWeeks , Date.IsInNextNYears , Date.IsInNextQuarter , Date.IsInNextWeek , Date.IsInNextYear , Date.IsInPreviousDay , Date.IsInPreviousMonth , Date.IsInPreviousNDays , Date.IsInPreviousNMonths , Date.IsInPreviousNQuarters , Date.IsInPreviousNWeeks , Date.IsInPreviousNYears , Date.IsInPreviousQuarter , Date.IsInPreviousWeek , Date.IsInPreviousYear , Date.IsInYearToDate , Date.MonthName , DateTime.IsInCurrentHour , DateTime.IsInCurrentMinute , DateTime.IsInCurrentSecond , DateTime.IsInNextHour , DateTime.IsInNextMinute , DateTime.IsInNextNHours , DateTime.IsInNextNMinutes , DateTime.IsInNextNSeconds , DateTime.IsInNextSecond , DateTime.IsInPreviousHour , DateTime.IsInPreviousMinute , DateTime.IsInPreviousNHours , DateTime.IsInPreviousNMinutes , DateTime.IsInPreviousNSeconds , DateTime.IsInPreviousSecond , List.FindText , List.MatchesAll , List.MatchesAny , List.NonNullCount , List.Range , List.RemoveItems , List.RemoveLastN , List.ReplaceValue , Replacer.ReplaceValue , SqlExpression.SchemaFrom , Table.AddColumn , Table.AlternateRows , Table.Buffer , Table.ColumnCount , Table.ColumnsOfType , Table.CombineColumns , Table.Contains , Table.ContainsAll , Table.ContainsAny , Table.DemoteHeaders , Table.DuplicateColumn , Table.ExpandListColumn , Table.ExpandTableColumn , Table.FillUp , Table.FindText , Table.FirstValue , Table.HasColumns , Table.InsertRows , Table.IsDistinct , Table.IsEmpty , Table.Last , Table.LastN , Table.MatchesAllRows , Table.MatchesAnyRows , Table.Max , Table.MaxN , Table.Min , Table.MinN , Table.Partition , Table.PositionOf , Table.PositionOfAny , Table.PrefixColumns , Table.Profile , Table.Range , Table.RemoveLastN , Table.RemoveMatchingRows , Table.RemoveRows , Table.Repeat , Table.ReplaceMatchingRows , Table.ReplaceRows , Table.ReplaceValue , Table.ReverseRows , Table.Schema , Table.SplitColumn , Table.ToColumns , Table.ToRows , Table.TransformRows , Table.Transpose , Table.View , Text.AfterDelimiter , Text.BeforeDelimiter , Text.BetweenDelimiters , Text.Format , Type.TableSchema