daveliepmann

When to use assert?

In JVM Clojure, Exceptions are for operating errors ("something went wrong") and Assertions are for programmer and correctness errors ("this program is wrong").

An assert might be the right tool if throwing an Exception isn't enough. Use them when the assertion failing means

• there's a bug in this program (not a caller)
• what happens next is undefined

daveliepmann

(ns sample.load-edn
  "Load EDN from asset on startup"
  (:require
   ["package:flutter/material.dart" :as m]
   ["package:flutter/widgets.dart" :as f.widgets]
   ["package:flutter/services.dart" :as f.services]
   [cljd.flutter :as f]
   [cljd.reader]))

daveliepmann

Speech at the American Legion

Hans Liepmann, circa 1946-8

During the long weary days and nights I spent in the Army, I had ample time to think about my American citizenship. I knew Germany under the Kaiser, during the Weimar Republic, in the beginning of Hitler’s regime and I saw it again at the end of it. Therefore, I had quite some occasion to compare it with America and maybe some of my experiences and observations will be interesting for you to hear. I consider it a great honor to be asked by the American Legion to talk to you and I thank the chairman very much.

You heard in the introduction a short outline of my story but I may be permitted to say a few more words about it. In 1933, when Hitler was chancellor, I received a letter from the government that from the next day on I, being a Jewish physician, was not permitted any longer to take care of patients who were members of the medical insurance companies. That was not so terribly bad in itself. But at that

daveliepmann

;; make sure your ns has `(:import [org.tensorflow DataType Graph Output Session Tensor])`
;; or if in REPL, evaluate `(import [org.tensorflow DataType Graph Output Session Tensor])` first

;; Construct a graph to add two float Tensors, using placeholders.
(let [g (Graph.)
      s (Session. g)
      x (-> (.opBuilder g "Placeholder" "x")
            (.setAttr "dtype" DataType/FLOAT)
            (.build)
            (.output 0))

daveliepmann

Converting Java to Clojure for Non-Java Folks

Some simplified examples of how to read Java and turn it into Clojure. Intended for Clojurists without a background in Java. Based on clojure.org's Java Interop reference.

Consider reading: https://stackoverflow.com/questions/11993077/difference-between-static-methods-and-instance-methods

Calling methods of an instance

Say we come across some Java that calls a method on a string literal:

daveliepmann

;; 300x300 seems to be about where performance starts to degrade.

(let [i (cell (interval :frame inc))]
  (cell 
    (apply layer
      (for [x (range 0 300 20)
            y (range 0 300 20)]
        (let [angle (* (/ 3.14 180) (+ @i x y))]
          (position (+ x (* 15 (Math/cos angle)))
                    (+ y (* 15 (Math/sin angle)))

daveliepmann

;; # One-Rep-Maximum Calculator

;; People who strength train often want to predict the maximum weight they could lift for one repetition. This is because actually making a maximal attempt is tiring, slightly risky, and difficult to repeat. Let's see how to guess our "1RM" using sub-maximal attempts.

;; If you need to re-evaluate one of the code blocks below, put your cursor in it and press `Control-Shift-Enter` (`Command-Shift-Enter` on Mac).

;; ## Equations

;; There are many equations used to predict one-repetition maximum based on the greatest weight lifted for two to ten reps. All are unavoidably inexact. One popular method for determining your 1RM comes from Baechle, Earle, and Wathen (2000):

daveliepmann

;; # Data Structures
;; 
;; So far, we've dealt with discrete pieces of data: one number, one
;; string, one value. When programming, it is more often the case that
;; you want to work with groups of data.
;; 
;; Clojure has great facilities for working with these groups, or
;; *collections*, of data. Not only does it provide four different types
;; of collections, but it also provides a uniform way to use all of these

daveliepmann

;; Colorization functions, demonstrated with ranges
(map #(colorize % (square 50))
     (map #(hsl % 100 50) (range 0 250 25)))

(map #(colorize % (square 50))
     (map #(hsl 120 % 50) (range 0 250 25)))

(map #(colorize % (square 50))
     (map #(hsl 120 50 %) (range 0 100 10)))

daveliepmann

;; # A whirlwind tour of Maria.cloud

;; ### 🔺 🔷 🔴 🔶 🔵 🔻
;; The first thing you should do is draw something:

(circle 50)

;; we provide an extensive picture language:

(layer