FParsec2.fs

open FParsec

[<RequireQualifiedAccess>]
type QueryComparison = 
    | Equal
    | NotEqual

[<RequireQualifiedAccess>]
type TableOperators =
  | And
  | Or

[<RequireQualifiedAccess>]
type Filter =
  | Property of name: string * QueryComparison * value: string
  | Combined of Filter * TableOperators * Filter

let letterOrNumber = asciiLetter <|> digit
let manyLettersOrNumbers = many1Chars letterOrNumber
let manyCharsNotSingleQuote = (many1Chars (noneOf [ '\'' ]))

let stringParser =
  let quote = pchar '\''
  between quote quote manyCharsNotSingleQuote |>> (string)

let fieldValueParser = stringParser

let queryComparisonParser =
  [ ("eq", QueryComparison.Equal); ("ne", QueryComparison.NotEqual) ]
  |> List.map (fun (toMatch, qc) -> stringReturn toMatch qc <?> (sprintf "%O" qc))
  |> choice

let propertyParser =
  let name = manyLettersOrNumbers .>> spaces <?> "Name"

  let queryComparison = queryComparisonParser .>> spaces <?> "QueryComparison"

  let filterValue = fieldValueParser <?> "FilterValue"

  name .>>. queryComparison .>>. filterValue |>> (fun ((n, qc), fv) -> Filter.Property(n, qc, fv))

let opp = new OperatorPrecedenceParser<Filter, unit, unit>()
let expr = opp.ExpressionParser

opp.AddOperator(InfixOperator("and", spaces, 1, Associativity.Left, fun left right -> Filter.Combined(left, TableOperators.And, right)))
opp.AddOperator(InfixOperator("or", spaces, 2, Associativity.Left, fun left right -> Filter.Combined(left, TableOperators.Or, right)))

opp.TermParser <- choice [propertyParser; expr]

let filter = spaces >>. expr .>> spaces .>> eof

let parse query = run filter query

[<EntryPoint>]
let main argv =
  parse "Name eq 'Dave' and Colour ne 'red'" |> printfn "%A"


  (*

    Failure:
    Error in Ln: 1 Col: 16
    Name eq 'Dave' and Colour ne 'red'
                   ^
    Expecting: end of input

  *)

  0 // return an integer exit code