I'm actually quite conscious of cons-ing, but I also believe that obsessing about cons-ing leads to premature optimization and far greater numbers of bugs.
We are fortunate to have the benefit of his wisdom and it occurs to me that we can keep talking past each other enjoyably for weeks like this so i will not suggest we try to establish a concrete example where he would code append and I would code nconc and ruin all the fun. But it is a good question especially if we agree (we do) that as a rule the functional paradigm utterly Rocks the Casbah so how on earth am I going to get a list back from some function I call and not be free to nconc it? The moral being I am right (will it never end?): if we try to find a point of Actual Disagreement(tm) we will fail so let us not.
Getting back to the fun abstract theoretical conflict, the problem is a policy of copying which leads straight to the solar power objection aka death by a thousand cuts which in turn leads us back to the simple question of why we do not just code the right operator at every turn? Genius is in the details which means we are always on our game bringing me to Mariano Rivera.
For those who do not know Mariano plays baseball and is starting to be called the best ever at his position, namely "closer" which means we won the first eight innings and do not want to lose the game please do the rest and he does. Even in the seventh game of the World Series that he lost every hitter broke their bat but the three balls involved known in the game rather morbidly as "dying quails" found their way to the grass. Hard to feel bad about shattering three bats. I digress, Mo is good.
Genius. Details. The great Nconc vs Append War, Roberts-Tilton III, nothing like this since Ali-Frazier, Affirmed and Alydar.
It was Just Another Game. The Yanks had won, Mo had saved. They always collar some poor sod and keep him from his shower and car service home to make those of us who pay to watch baseball on cable TV feel better and tonight poor Mariano's number (42!) came up and by the grace of God I pulled my face out of a carton of cold noodles with seame sauce just in time to witness a perfect moment in sports broadcasting and as well a master class in excellence any time any where.
The announcer on the field for the interview went for a home run question, something way more astute than the usual "How did it feel getting the big out?" and he came up with a beaut:
"Billy Bob is a rookie and you have never faced him before, there must not be much of a book on him," the announcer observed. "Was it tougher facing an unknown quantity?".
"No," Mariano replied. "I went out during batting practice to watch him hit."
Mariano's disclosure that as a Hall of Fame shoe-in and multi-millionaire perennial All-Star participant he had looked down at the lineup and seen an unfamiliar name and broken off his clubhouse routine to go watch some ridiculous kid take batting practice had no small effect on our seasoned, professional, expert baseball announcer:
"You did that?!!!!!!". He blurted out, hopping a little in the air, lurching towards Mariano. "You went out to watch him take batting practice?!!"
Now it was Mariano's turn to be amazed, leaning back a little to create a margin of safety.
"Of course," he replied. "I get paid a lot of money."
Doodleoodleoodleoodleoodleoooo. Game over. The announcer (and I, I confess) had been seriously schooled.
We sit at home and watch these athletes precisely because what they do is so wonderful to us and we endow them in our minds with magical and wonderful qualities because at an early age we were robbed of angels and dragons and Santa Claus and even monsters in the closet and trolls beneath the bridge and then every once in a while we learn that the miracle strikeout we saw with the bases loaded happened because a multi-millionaire punched the time clock, checked his glove for broken laces, sharpened his spikes, and checked the opposing team's roster for any names he did not know.
I say learn the damn language.