Pudu Playground

Program source

// JSON and CSV
// Reading a JSON document into a record, writing one back, and totalling a CSV table by column.
module Main

import Std.Csv as Csv
import Std.Io as Io
import Std.Json as Json
import Std.Map as Map
import Std.Option as Option
import Std.Text as Text

type User = { name: Str, age: Int }

const DOCUMENT: Str = "[\{\"name\": \"Ada\", \"age\": 36\}, \{\"name\": \"Grace\", \"age\": 45\}, \{\"name\": \"Nobody\"\}]"

const SHEET: Str = "name,team,points\nada,red,12\ngrace,blue,30\n\"lin, jr\",red,8\n"

// Each ? leaves with None when a field is missing or has the wrong kind.
fn userFrom(value: &Json.Json) -> Option[User] {
  let name = Json.asText(&Json.field(value, "name") ?) ?
  let age = Json.asInt(&Json.field(value, "age") ?) ?
  Some(User{name: name, age: age})
}

fn userJson(user: &User) -> Json.Json {
  Json.object(&[("name", Json.Text(user.name)), ("nextBirthday", Json.Number(user.age + 1))])
}

fn main() -> Int {
  let entries = match Json.decode(DOCUMENT) {
    case Ok(Json.List(items)) => items
    case Ok(_) => { return 1 }
    case Err(problem) => {
      let _explained = Io.writeLine(Json.explain(&problem))
      return 1
    }
  }
  var users: Array[User] = []
  for entry in entries {
    match userFrom(&entry) {
      case Some(user) => { users = users.push(user) }
      case None => { let _skipped = Io.writeLine("skipped an entry without a name and an age") }
    }
  }
  let _read = Io.writeLine("read {users.length()} users")
  let _written = Io.writeLine(Json.encodePretty(&Json.list(&users.map(|user: User| userJson(&user)))))

let table = match Csv.parseTable(SHEET) {
    case Ok(held) => held
    case Err(_) => { return 1 }
  }
  var totals: Map[Str, Int] = mapOf([])
  for row in Csv.records(&table) {
    let team = Map.getOr(&row, "team", "none")
    let points = Option.unwrapOr(Text.wholeOf(Map.getOr(&row, "points", "0")), 0)
    totals = totals.insert(team, Map.getOr(&totals, team, 0) + points)
  }
  let _totals = Io.writeLine("points by team: {totals}")
  let _names = Io.writeLine("names: {Option.unwrapOr(Csv.column(&table, "name"), [])}")
  0
}

Output

Press Run to see what the program prints.

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Using the playground

Output