Code As Data in F#

codeasdata.fs

(* Type definitions *)

// A list of functions that take the current context (TDS return),
// and return true if the column is supposed to be visible right now
type IsColumnVisible = (TdsReturn -> bool) list

// List of functions that take a data row (generic type 'T)
// and return true if the current column is supposed to be editable
type IsColumnEditable<'T> = ('T -> bool) list

// This is a specification for a single column
// A 3-element tuple, containing a expression that will identify the field,
// and visibility / editability selectors
type ColumnSpec<'T> = (Quotations.Expr * IsColumnVisible * IsColumnEditable<'T>)

(* Pre-defined functions *)

// Pre-defined column visibility specifiers
let showAlways     = fun (t : TdsReturn) -> true
let showForRevised = fun (t : TdsReturn) -> t.IsRevised
let showForGovt    = fun (t : TdsReturn) -> t.IsForGovernment

// Pre-defined column editing specifiers
let editAlways            = fun (d : Deduction) -> true
let editWhenNil           = fun (d : Deduction) -> d.Amount = 0
let editWhenDateIsPresent = fun (d : Deduction) -> d.Date |> Option.isSome

(* Actual UI Specification *)

// Final UI Specification
let (deductionColumns : ColumnSpec<Deduction> list) = [
    <@ fun (d) -> d.Date @>        , [ showAlways ]                   ,  [ editAlways ]
    <@ fun (d) -> d.SectionCode @> , [ showForRevised ]               ,  [ editWhenNil ]
    <@ fun (d) -> d.Amount @>      , [ showForRevised ; showForGovt ] ,  [ editWhenNil ; editWhenDateIsPresent  ]
]