This letter suggests that Dijkstra's tone was a function of intended audience: the aphorisms which inspired the nano-Dijkstra (as measure of arrogance) were intended for peers, Who Should Have Known Better; the supportive encouragement was intended for a junior, Who May Yet Someday Do Something Interesting.
Too often i see people being dismissive of Dijkstra because of his aphorisms, they don't understand the context that drove it.
In my mind he was a "True Perfectionist" who demanded Perfection of himself and everybody else. It was a rare uncompromising and mathematically focused mind well suited to the then nascent "Computing Science" field.
while there is something to this, it is also important context that io was already something very interesting indeed; though raph was 19 he was already advancing human knowledge in a way that many of dijkstra's supposed peers were failing to do
it is a shame that io is not more well known, because it is a brilliant achievement; by virtue of a simple syntactic trick it turns explicit cps code from its usual impenetrable form into something quite readable
Viewing continuations as the "mother of all monads", this work (1989) could have anticipated Moggi (1991) if there had been continued development in that direction!
(it would've taken much more work though, as IIRC EWD noted Io as presented wasn't properly associative in ';')
that's right, it's unrelated to steve dekorte's io, which is also kind of cool but not in the same fundamental way
levien's io is maybe less practical, though it's hard to tell since nobody's done the work of putting together an implementation with batteries
my notes on it from sometime in 02007–02009 are at https://dercuano.github.io/notes/raph-io.html but i didn't have a copy of the actual paper at the time, just some badly ocred code and quotes from the paper, plus some commentary
