Here's how I came up with this line.
1. I held down my shift key and mashed a bunch of keys on the top row.
2. I added a couple of common key words: most examples like map and range so I used them.
3. I evened out the parentheses and added a couple of brackets.
That's about as much sense as I can make out of the function language tutorials I've seen. They always seem to have more obtuse symbols and meta characters than real names and keywords.
So what's up with that?!?