Let the type system do it for you

Presentation at Functional Media, ITV, London.
http://www.meetup.com/Functional-Media/events/137916712/

Transcript

1. Richard Dallaway @d6y www.underscoreconsulting.com Let the type system do it for you
2. csv( List("Date","Ratio X"), List("Mon","6") :: List("Tue","-2") :: Nil ) Date Ratio X Mon 6 Tue -2
3. csv( List("Date" ), List("Mon","6") :: List("Tue","-2") :: Nil ) Oops and so… ? Date Mon 6 Tue -2
4. def csv( hdrs: Seq[String], rows: List[Seq[String]]) : String = ...
5. def csv( hdrs: Seq[String], rows: List[Seq[String]]) : String = ... import shapeless._ import syntax.sized._
6. def csv[N <: Nat]( hdrs: Seq[String], rows: List[Seq[String]]) : String = ... import shapeless._ import syntax.sized._
7. def csv[N <: Nat]( hdrs: Sized[Seq[String], N], rows: List[Seq[String]]) : String = ... import shapeless._ import syntax.sized._
8. def csv[N <: Nat]( hdrs: Sized[Seq[String], N], rows: List[Sized[Seq[String], N]]) : String = ... import shapeless._ import syntax.sized._
9. csv( Sized("Date","Ratio X"), Sized("Mon","6") :: Sized("Tue","-2") :: Nil ) Date Ratio X Mon 6 Tue -2
10. csv( Sized("Date" ), Sized("Mon","6") :: Sized("Tue","-2") :: Nil ) Type mismatch at compile time found: Sized[IndexedSeq[String],shapeless.nat._1] required: Sized[Seq[String],Succ[_ >: shapeless.nat._1 ...] Oops
11. class SizedOps[A, Repr, N <: Nat] ... { def head(implicit ev : _0 < N) : A = r.head def tail(implicit pred : Pred[N]) = wrap[Repr, pred.Out](r.tail) ... }
12. @d6y www.underscoreconsulting.com Less code Clearer intent Summary