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stettix /
Last active March 20, 2024 17:45
Things I believe

Things I believe

This is a collection of the things I believe about software development. I have worked for years building backend and data processing systems, so read the below within that context.

Agree? Disagree? Feel free to let me know at @JanStette. See also my blog at


Keep it simple, stupid. You ain't gonna need it.

stettix / Backfiller.scala
Created June 3, 2019 11:35
Backfiller command line tool
package backfiller
import aws.AWS
import cats.effect.{ExitCode, IO, IOApp}
import com.amazonaws.AmazonServiceException
import com.amazonaws.retry.RetryUtils
import{ClusterDefinition, EmrStep, RunConfiguration}
import fs2.{Chunk, Pure, Stream}
import spark.implicits._
// Input data
val identity =
.select("id", "account_created", "last_active_date", "primary_email_address")
stettix / gist:6105671
Created July 29, 2013 16:41
Pattern matching in eval()
def eval(expr: Expr, env: Env): Expr = expr match {
// ...
case "cons" :: arg1 :: arg2 :: Nil => eval(arg2, env) match {
case l: List[Expr] => eval(arg1, env) :: l
case arg => throw new IllegalArgumentException(s"Second argument to 'cons' should be list, was: '$arg'")
case "cons" :: args => throw new IllegalArgumentException(s"Invalid arguments to 'cons': $args")
case "null?" :: head :: Nil => eval(head, env) == List()
case "null?" :: _ => throw new IllegalArgumentException("Expected exactly one argument for 'null?'")
// ...