[racket-dev] intro videos

From: Guillaume Marceau (gmarceau at gmail.com)
Date: Fri Jul 15 01:02:15 EDT 2011

On Thu, Jul 14, 2011 at 1:42 PM, Eli Barzilay <eli at barzilay.org> wrote:
> Yes -- paredit is exactly an attempt to get the always-balanced
> benefits of structured editing, without an actual structure editor.

Yes, but paredit still gets its priorities backward. You want to have
the most commonly used edit operations on the easiest chords (or
without any chord at all, if you are trying to avoid RSI.) In paredit,
keystrokes to edit sexp are heavily chorded, and keystrokes to edit
single-characters are simple, even though single-char only occur when
fixing typos in identifiers, which is quite rare when using

Moving forward by one sexp in paredit is CTRL-ALT-F (ouch). In
DivaScheme it's just L.
Moving forward by two chars in paredit is RIGHT, RIGHT. In DivaScheme

On Fri, Jul 15, 2011 at 12:36 AM, Neil Van Dyke <neil at neilvandyke.org> wrote:
> The reason has to do with the stress of stretching/twisting people do with
> their hands for multi-key combination, is my layperson's understanding.
> Around the time, when CTS and other RSIs were getting a lot of attention, I
> heard this from multiple credible sources, and the knowledge seemed to work
> for me.

Yes. Any deviation of the wrist away from neutral by more than 5°
correlates with higher incidence of RSI, and there are biological
phenomenon that have been observed that give credence to a causal

One of the best such study is

     A Prospective Study of Computer Users, by Gerr, Marcus, Ensor,
Cohen, Edwards, Gentry, Ortiz, Monteilh, AJIM 41:221-235 (2002)

Over a period of 38 months, they followed 632 computer professionals
who were pain-free at the beginning of the study. By observing who
developed pain, and comparing their work habits to those of the
pain-free workers, the study was able to measure the risk factors
associated with many different postures or practices. Their
recommendations were (starting with the most effective):

Keep your elbows slightly open, at around 121° (reduced the risk by 84%)
Leaves more than 12 cm between the edge of the table and the "J" key
(... by 62%)
Don't use your neck to hold the phone (... by 60%)
Avoid keyboard wrist rests (... by 48%)
Don't bend your wrists when holding the mouse. Keep it within 5° (... by 45%)
Strike the keys with a light touch, with less than 48 g of pressure (... by 40%)
Raise the screen so that your neck tilt by less than 3° (... by 36%)
Rest your elbows or forearms on the chair armrests, or on the desk
itself (... by 35%)
Use a keyboard that is less than 3.5 cm thick (... by 35%)
Keep the keyboard slightly lower than your elbows (... by 23%)
Avoid resting your hands on the leading edge of your desk, or pad the
edge (... by 22%)

The highest incidences were for females, for people over 30, and for
people who type more than 20 hours per week. The risk factor of these
groups was about twice that of the general population.

I have an entire article on RSI on my website, for people who are
interested: http://gmarceau.qc.ca/articles/your-wrists-hurt-you-must-be-a-programmer.html

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