Comments on: Technical debt (or, mortgages in Haskell)

By: Simon

Simon — Mon, 07 Dec 2009 23:54:59 +0000

Very interesting, thanks! Will have to see if there are synergies with hledger.

By: daryoush

daryoush — Tue, 24 Nov 2009 06:39:46 +0000

Thanks for the explanation of the Basic’s NUM instance. I have been looking at that code for last few days trying to make sense of it, your explanation helped.

I am curious about you comment on the Arrow style for the DSL. Can you elaborate and/or give a reference to the DSL syntax in Arrows.

Thanks

Daryoush

By: Paul Hollingsworth

Paul Hollingsworth — Thu, 19 Nov 2009 00:06:23 +0000

Note that you can define a closed form for a linear recurrence relation.
So, for example if you had Balance(0) = Initial, Balance(n) = Rate * Balance(n-1) + Repayment then there’s a closed form solution for this Balance(n): Balance(n) = Initial * Rate^n + Repayment * ((1-Rate^n)/(1 – Rate))… Useful if you then want to “solve” for n, Repayment etc. So, my challenge to you is: Write a program to “automatically” solve a linear recurrence relation using the method described here http://en.wikipedia.org/wiki/Recurrence_relation!

By: Jeremy

Jeremy — Wed, 18 Nov 2009 17:38:30 +0000

“From stuff I’ve read previously, I think my two options are… Lisp-like…Arrow-like.”

You might find another option from Elliott et. al. at http://conal.net/papers/jfp-saig/. If you can represent your DSL as haskell functions that range over term types, then you can apply a literal value to evaluate it, or apply a variable to inspect it. I’ve had good luck with this approach in a DSL of my own.

By: Andrew

Andrew — Tue, 17 Nov 2009 21:02:03 +0000

Reid: Cool, thanks for that – I didn’t know that sections could be used in that way.