ocaml code generator

codegen.ml

let prologue =
  {|
(* This code is automatically generated *)
let string_of_string x = x
|}

let epilogue =
  {|
let print t = pp Format.std_formatter t

let () =
  Csv.Rows.load ~has_header:true "datainput.csv"
  |> List.map decode
  |> List.iter print
|}

let map_hstype = function
  | "String" ->
      "string"
  | "Int" ->
      "int"
  | "DayOfWeek" ->
      "string" (* for now *)
  | t ->
      failwith ("Unknown type: " ^ t)

let () =
  let inpath = Sys.argv.(1) in
  Stdio.Out_channel.with_file Sys.argv.(2) ~f:(fun out ->
      let print s = Printf.fprintf out "%s\n" s in
      print prologue ;
      let schema =
        Csv.Rows.load ~has_header:true inpath
        |> List.map Csv.Row.to_list
        |> List.mapi (fun i -> function
             | [field; typ; _parser] ->
                 let i = i + 2 in
                 let field = String.lowercase_ascii field in
                 (i, field, map_hstype typ)
             | line ->
                 failwith ("Unknown line format: " ^ String.concat "," line))
      in
      print {|type t = { |} ;
      List.iter
        (fun (i, f, t) ->
          Printf.sprintf {|# %d "%s"|} i inpath |> print ;
          let sep = if i > 2 then "; " else "" in
          Printf.sprintf "%s%s: %s\n" sep f t |> print)
        schema ;
      print {| } |} ;
      print {|let decode row = |} ;
      List.iteri
        (fun j (_i, f, t) ->
          Printf.sprintf {|let %s = Csv.Row.get row %d |> %s_of_string in|} f j
            t
          |> print)
        schema ;
      print {|{|} ;
      schema
      |> List.map (fun (_, f, _) -> f)
      |> String.concat "; " |> print ;
      print {| }|} ;
      print {|let pp = Fmt.Dump.record [|} ;
      List.iter
        (fun (_, f, t) ->
          Printf.sprintf "Fmt.Dump.field \"%s\" (fun t -> t.%s) Fmt.%s;\n" f f t
          |> print)
        schema ;
      print {| ]|} ;
      print epilogue)

datainput.csv

dune

(executable
 (name codegen)
 (modules codegen)
 (libraries stdio csv)
 )

(rule
 (target generated.ml)
 (deps input.csv)
 (action (run %{exe:codegen.exe} %{deps} %{target}))
)

(tests
 (deps datainput.csv)
 (names generated)
 (modules generated)
 (libraries fmt csv)
 )

input.csv

dune runtest