Clojurians Log v2

This question is mostly related to a database, not Clojure I think. Each client has accounts, and each account has currency. Then, you have a table that stores history of account withdrawals and replenishments. It's a matter of SQL stored function that accepts an account id, a sum, and a currency and checks if the currency matches the currency of the account. Otherwise, the function throws an exception

I like to use int (which is a Java long) rather than float or a BigDecimal type. Keep all monetary stored data as a type without decimal places in the database - so cents or pesos or whatever. For presentation or reading input convert to the integer type as soon as the number is within your program. After multiplication or division you are going to have to round.

@teodorlu recently designed a sweet open ended system for working with units: https://github.com/teodorlu/munit

Happy to help if you'd like to give Munit a go! The core idea is small: 1. Represent numbers with units as Clojure data 2. Provide math operators for working on that data structure. There are other Clojure unit libraries too, but they generally work on a custom type for numbers with units, and a larger API surface than data + arithmetic operations.

Munit doesn't care if your base units are Euros, meters or apples, so there's no arbitrary unit system restrictions in place.

(+ [1 'apple] [1 'apple])
;; => [2 apple]

(+ [1 'apple] [1 'orange])
;; => Execution error (ExceptionInfo) at munit.impl/add (impl.clj:106).
;;    Cannot add quantities of different units

So I take it this is more of a DSL-ish approach?

No DSL, it's lighter! Units are plain Clojure data, and + is a normal function, munit.units/+.

Sweet. Even better.

Aaand, I was just going to ask whether you have any property-based tests, but then I found it as a to do in the code^^

You surely wouldn't mind a PR in case I find some time to build a few of those?^^

I'd happily take a test.check generator for Munit! Not sure about tests, I wasn't able to convince myself of any interesting properties to test. If your generator & properties does find any bugs, I'll definitely merge!

I'll look into it! My question might well have been a case of hammer-nail-fallacy, so what's there might just be enough, but we'll see^^

Let me know how it goes! Regardless of PRs, I'm very much interested in helping you get started, and want to know if you hit any friction!

here's an example of a doityourself approach: https://github.com/potetm/fusebox/blob/0d3605442f2c5e812284678f69924c5fd6588179/src/clojure/com/potetm/fusebox.clj#L17-L44

though I later abandoned it in favor of just using millis for everything (this was time only), so ymmv

First thing that I noticed: is there an intended way of defining new units (not derived)? So I wanted to use this for money, I'd probably do something like (def $ (units/* 1 1)). Is that how you'd imagine it?

If you're asking me and not potetm — base units in Munit are symbols. You can either inline the symbol:

(* 2 [7 '$])
;; => [14 $]

;; currencies.clj
(ns currencies)

(def $ '$)
(def EUR 'EUR)

(require 'currencies)
(* [7 currencies/$]
   [0.9 (/ currencies/EUR currencies/$)])
;; => [6.3 EUR]

I generally prefer putting base units in a namespace, that way currencies/EURR fails fast (typo), and I can use static analysis to find where "EUR" is used.

If you define dollars as (def $ (units/* 1 1)), $ will bind to the number 1! So not a Munit base unit.

(spec/def ::body
  (spec/cat :params (spec/spec :clojure.core.specs.alpha/param-list)
            :body (spec/* any?)))
(spec/def ::impl
  (spec/cat :hook-name simple-symbol?
            :hook-tail (spec/+ ::body)))
(spec/def ::defhook-args
  (spec/cat :defhook-name simple-symbol?
            :hook-impls (spec/+ ::impl)))

running

(spec/explain
 ::defhook-args
 '(profile (pre-test-suite [_config m] (start m))))

(pre-test-suite [_config m] (start m)) - failed: simple-symbol? in: [1] at: [:hook-impls :hook-name] spec: :lazytest.hooks/impl

why is ::impl being treated as inline to the :hook-impls part of s/cat?

after poking around, i figured out i can say :hook-impls (spec/+ (spec/and seq ::impl)) to make it work, but i don't understand why

oh, i need :hook-impls (spec/+ (spec/spec ::impl)) because i'm starting a new nested context

there is a spec for protocols in a jira if you wanted to swipe that btw

regex specs all combine into one "nesting level", s/spec can be used to create a new one

well, maybe there isn't a jira for that, can't find it now. Sure thought I had worked on it at some point

there's one for extend-protocol but i don't think there's an attached patch: https://clojure.atlassian.net/browse/CLJ-2836

there's no doubt other tickets i don't remember/know about