examples

Examples

• Using Prisms with Sum Types

Conventions and the "why" behind them

The examples are meant to be read from top to bottom.

Every example is self-contained and can be imported into the repl. The top of an example module will have a comment like this:

{-   If you want to try out examples, paste the following into the repl.

import PrismsForSumTypes
import Data.Lens
...
-}

(Tip: because each line is self-contained, you don't need to use :paste.)

The modules contain both definitions of optics and sample uses. The sample uses are executable code that look like this:

s1 :: Maybe Color
s1 = preview solidFocus (Solid Color.white)
-- (Just rgba 255 255 255 1.0)

Why?

1. The second line can be pasted into the repl without needing to use :paste. (I usually don't copy the s1 = because I prefer seeing the results immediately. All types in the examples implement show, making that painless.)

2. The sample uses are executable code so that the compiler checks them and -- more importantly -- so that they stand out from the surrounding commentary. That makes the files more easily scannable when you're refreshing your memory about a particular function (assuming you use a syntax highlighter).

3. The name-value bindings (like s1) are clutter, but required by the compiler. Most of the type annotations are also clutter, but are required to prevent compiler warnings in, for example, pulp build.

4. The expected value is on a new line, rather than appended to the end of the second line, because it's visually easier to scan down a line than scan right for a -- pattern.

   "Comfort is the key." -- Prof. Dawn Marick, DVM, MS, DACVIM (LAIM)