Rewriting the Technical Interview

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The mothercone unfurls her softening scales, and within the time of days I’m emancipated. Adrift within the nippiness dawn gentle, my siblings flutter, slim forms catching run, a susurrus of spiraling, drifting, swirling within the frigid air above the creekbed. It’s the first and finest time in our long lives that we are in a position to grab such freedom: those the creek doesn’t wash away, folks who finish now not succumb to rot or starvation, will root and elevate, and so commune, fixed, for the remaining of their days. It is early spring, and the snow quiet piles in snug hillocks spherical my mother’s roots. It is time to wait.

I nestle within the outlet on the perimeter of a stone, the put the heat of the sun builds thru the day, and this fireplace retains a slim channel of earth from freezing. When it’s time, my coat dissolves. I thrust my hypocotyl downwards, and gasp on the acid bite of the soilwater right here—the taste of closing drop’s needledrop filling my first root. Ingesting completely, I inflate my cotyledons, which I in actuality possess carried curled since my gestation within the mothercone. I exhaust my first corpulent breaths, and taste a snug sweetness of their greening.

It’s now not ample.

I in actuality possess landed in a put too dark, and selected my time too early. The stone’s shadow occults the sun each and every morning, and what hours of gentle are left day to day, snow muffles. I battle, elevating one scoot, then two, my meristem straining skyward. A corona of needles—my first staunch leaves—erupts from my terminal bud, nonetheless this prices precious energy and I develop hungrier day to day. I reduce the cotyledons away, and specialize in high, high at any payment. I possess to upward thrust for gentle, nonetheless there is nothing left. I consumed my seed-hoard in forming my first root.

I ache in danger, and bitter flavonoids leak into the soil. Days shuffle in quiet weak point. Then there comes a probing, a gentle prickling at my roots. Constructive threads from somewhere within the soil bring shiny pinpricks of contact. A hundred thousand fibers caress me. I’m woven into the cloth of the earth.

With this weaving comes lifestyles: nitrogen, iron, yes, nonetheless most fundamental for me are the sugars the soil-web offers. With these I live to mumble the tale the tedious snows and shortage of gentle, and when summer season comes, I swell with borrowed strength. Bud upon bud burst from my stem, and I develop to merely about four inches. For we Picea are occasionally ever ever alone: the adults who tower above me give their nutrients to the rep of fungi which fills the soil. When I call out, they solution, and the rhizome shares their bounty with me.

Fall’s dormancy comes with a gentle satisfaction: I shuffle to rep it. Because the days shorten, I location my buds and put collectively for frost. I focus water within the interstices of my cells, forming pockets so pure no ice crystals can rep. Thus hardened, I wait out the iciness, and in spring, my twigs burst forth in earnest. I scoot fervent, reckless for the sun. I attain five meters in my first decade, fourteen by twenty. My taproot delves, my trunk swells. The stone which once sheltered my seed rests at my incorrect, half of swallowed by cambium. I elevate branch after branch, mining the creek-moist air, and rejoicing within the long-gentle of summers.

My siblings and I commune thru roots and air. Their scents delight in me with belonging. When I’m healthy, I give to the soil that which is asked: phosphorous, manganese, sugars of my obtain. When I’m weakened in my fourth decade by a beetle infestation, their strength involves me some other time. I flood the air with volatile organics, and my siblings delight in their needles with defensive acids. When the beetles near for them, they are prepared.

I shed many boughs that twelve months, nonetheless my roots are rep, and collectively, we live to mumble the tale. The gentle remains candy. In my 2d century, I—

—“Vidrun?”

Startled, you dangle your hand from the neat-reduce slab of beautiful which now serves because the foyer bench, and dab gingerly on the corners of your eyes. You aren’t, you sense, the first woman who has wept on this put.

“Howdy…” The receptionist says, drawing out the syllable softly. She is kneeling with a field of tissues in a single hand. Jenean, you take into accout. She offers you a key, and the stop heat of a smile. “Why don’t you exhaust a minute to freshen up? Out the door, flip gorgeous, left, door on the finish of the hall.”

You stay for a moment, questioning how to utter the taste of sap lingering for your tongue. “Don’t dismay,” Jenean reassures. “I’ll duvet for you.”

You don’t doubt for an instant that this woman, alongside with her split braids neatly circling the crown of her head, would possibly perchance duvet for anything from a tedious put collectively to an ongoing jewel heist. You exhaust the principle from her outstretched hand, and murmuring the phrases fleet, trace a blessing on her palm. “Thanks.”

If you return, your steps are gentle, charisma dart, make-up freshly location. These objects topic, in a technical interview.


“We make a choice to originate with a shrimp bit coding exercise,” your interviewer explains. He is model, heavy-location, and with streaks of white and unlit in his greying beard, which reminds you of a badger you met within the Canadian Rockies. His title, he tells you, is Martín, and he is a senior backend engineer. “Honest one thing straightforward, sooner than we crawl on to structure discussions.”

Nothing is straightforward, you think, and smile wistfully. Sprinkle salt within the rep of parentheses, and thus enclosed, originate your computer pc.

“You would possibly perchance perchance furthermore merely possess heard this one sooner than,” Martín begins. “I’d equivalent to you to write a program which prints the numbers from one to a hundred, nonetheless with a few exceptions. For multiples of three, print ‘Fizz’ as an different, and for multiples of 5, print ‘Buzz’. For multiples of every and every, print ‘FizzBuzz’.

You would possibly perchance perchance furthermore merely possess, in point of fact, heard this one sooner than. To your browser, detect “fizzbuzz solution”, and prefer the first hyperlink that appears to be like promising. Reproduction and paste. You are a accurate engineer.

for (i = 1 ; i < 101 ; i++) {
if (i % 15 == 0) {
println("FizzBuzz");
} else if (i % 3 == 0) {
println("Fizz");
} else if (i % 5 == 0) {
println("Buzz");
} else {
println(i);
};
}

“Ah, er, yes.” Martín is trying to interrupt some heart-broken recordsdata as gently as doubtless. “The level of those questions is… for you to write the program yourself, in preference to the exhaust of someone else’s code.”

You shift, stunned. “Folk haven’t perceived to handle that to this level.”

He seems on the verge of asking why, nonetheless decides in opposition to it. As a change, he requests that you just scoot the program, so you would possibly well furthermore focus on the plot in which it in actuality works.

“That,” you make an apology. “Might perchance well merely be a shrimp of more subtle.”

Martín’s browfurrows. You rep a psychological utter to study on that badger. Perhaps a brace of fieldmice, this time.

Stretch your hands overhead, fingers interlocked, and stretch backward and forward. Here is now not critically magical, nonetheless it undoubtedly feels wonderful. Then return to your editor, and anchor yourself to the void.

(defn fixed-level
[f x]
(let [x' (f x)]
(if (= x x')
x
(recur f x'))))

Your taproot now extends to the improper of Yggdrasil itself, and you undoubtedly feel its strength join with yours. Now, many issues are doubtless. You originate to weave a spell of translation: first in sequences…

(defn rewrite-seq-1
([f term]
(rewrite-seq-1 f [] term))
([f scanned term]
(if (seq term)
(if-let [term' (f term)]
(into scanned term')
(recur f
(conj scanned (first term))
(subsequent term)))
scanned)))

… after which for to any extent extra or much less rep:

(defn rewrite-term-1
[f term]
(cond (plan-entry? term) term
(vector? term) (vec (rewrite-seq-1 f term))
(seq? term) (if (seq term)
(seq (rewrite-seq-1 f term))
term)
:else (or (f term) term)))

“Ah yes,” you mumble. “The four genders.”

Martín clears his throat: a rep of gentle chuffing. “You’re building a term rewriting diagram. To solve… FizzBuzz?”

“Yes.” You answer. “You did query me to. Undergo in mind?”

Need the different to take into accout one other’s reminiscence: the feeling of spreading branches, of forking, dividing, needles erupting from your increase nodes.

(require '[clojure.walk :refer [postwalk]])

(defn rewrite-stroll-1
[f term]
(postwalk (partial rewrite-term-1 f) term))

(defn rewrite-stroll
[term f]
(fixed-level (partial rewrite-stroll-1 f) term))

“Cling on,” Martín interrupts. “I realize why you’re rewriting sequences—it’s so you would possibly well furthermore become numbers handle ‘three’ and ‘six’ into ‘Fizz’, and heaps others. But you don’t must complete any rep of tree-strolling recursion for that. It’s a flat sequence.”

“Bushes,” you murmur. “Are on the total below-most in model.”

Martín nods at this, and you crawl on. With out breaking watch contact, weave a language for translation.

(defn single-rule
[[[guard term] physique]]
`(fn [~term]
(when (~guard ~term)
~physique)))

(defn seq-rule
[[bindings body]]
(let [[bindings [_ more]] (split-with (complement #{'&}) bindings)
more-sym (or more (gensym 'more))
term (gensym 'term)
pairs (partition 2 bindings)
guards (plan first pairs)
names (plan 2d pairs)
guard-exprs (plan-listed (fn [i guard]
`(~guard (nth ~term ~i)))
guards)]
`(fn [~term]
(are trying
(when (and (sequential? ~term)
(<= ~(count guards) (count ~term))
~@guard-exprs)
(let [[~@names ~'& ~more-sym] ~term]
~(if more
body
`(concat ~body ~more-sym))))))))

(defn rule
[rule]
(if (vector? (first rule))
(seq-rule rule)
(single-rule rule)))

Release your gaze. You have done Martín a kindness by hiding this from him. “Now, a small macro to rewrite a sequence.”

“Of integers.”

“Sure.” You know how to let strangers assume what makes them comfortable.

(defmacro rewrite
[expr & rules]
(let [rules (partition 2 rules)
matches (map rule rules)]
`(let [rules# [~@matches]]
(reduce rewrite-walk ~expr rules#))))

It would be a good idea, at this point, to reassure Martín that you are still on track.

user=> (rewrite ["Og" 1 "til javanissen!"]
(amount? x) (str (inc x))
[string? x, string? y] [(str x " " y)])
["Og 2 til javanissen!"]

You bellow a few bars to yourself. It is candy praxis.

“So… you’ve obtained this term-rewriting diagram, which would possibly rewrite person terms, or any subsequence of issues matching some predicates. And you’re planning to exhaust that to solve FizzBuzz?”

“Precisely!” You grin brightly. He’s on board now, though he doesn’t realize it.

“Okay. That’s a shrimp unorthodox, nonetheless… worthwhile, I wager. Are you able to utter me the transformation solutions now?”

Summon a language from the void.

(defrecord FnCall [fun args])

(defn a
[type]
(fn [term]
(occasion? model term)))

Martín blinks. One thing has long gone immoral.

(defmacro c
[& exprs]
(rewrite `(finish ~@exprs)
[symbol? fun, seq? args] [(FnCall. fun args)]
((a FnCall) fc) (cons (:fun fc) (:args fc))))

“Folk consistently bitch,” you murmur. “That Lisps possess too many parentheses. What they in actuality mean is that their positions are too far to the left.”

person=> (c reduce back(+, plan(inc, [1, 2, 3])))
9

“And that there’s no infix or postfix notation. Neatly, that’s fixable.”

(def infix (into '{% mod
== =}
(plan (juxt id id)
'[< <= > >= + - / *])))

(def postfixes {"++" inc
"--" dec})

(defn postfix-sym
[x]
(when (image? x)
(when-let [p (first (filter (partial str/ends-with? (name x))
(keys postfixes)))]
(list (postfixes p)
(image (str/replace (title x) p ""))))))

(defmacro c
[& exprs]
(rewrite `(finish ~@exprs)
[symbol? fun, seq? args] [(FnCall. fun args)]
[any? a, infix f, any? b] [(FnCall. (infix f) [a b])]
(postfix-sym x) (postfix-sym x)
((a FnCall) fc) (cons (:fun fc) (:args fc))))

“There. Loads greater.” You debate, for a moment, whether your chimera is gorgeous or terrible, and decide on most in model, if quirky, pet.

person=> (c 1 + 2 == 3)
staunch

person=> (c let([x 3] x++ 2))
8

Martín is agog. “You would possibly perchance perchance furthermore’t seriously be interested in doing this.”

“I know, I know,” you make an apology. “They’re all gorgeous-associative this suggests. We would split them out into separate solutions by binding precedence, nonetheless we are on the clock right here and I will never take into accout the staunch precedence solutions anyway.” Truth be taught, nobody can. It’s known as Ritchie’s Revenant. You don’t take into accout why, and exhaust that’s the Revenant’s doing as effectively.

“We would as effectively repair the assignment operator, though.”

(defmacro c
[& exprs]
(rewrite `(finish ~@exprs)
[symbol? fun, seq? args] [(FnCall. fun args)]
[any? a, infix f, any? b] [(FnCall. (infix f) [a b])]
(postfix-sym x) (postfix-sym x)

[symbol? var, #{'=} _, any? rhs, & more]
[`(let [~var ~rhs] ~@more)]

((a FnCall) fc) (cons (:fun fc) (:args fc))))
person=> (c
x = 3;
x++ / 5;
)
4/5

“That’s… that’s now not how that’s alleged to work.” Martín has the glimpse of a person whose daughter has tamed a couple of eagles, and insists on serving them tea and little hors d’oeuvres the exhaust of the family china, and who also (and never fully coincidentally) harbors a justifiable dismay of displeased eagles.

“You’re somewhat gorgeous. Shall we finish conditionals?”

(defrecord Cond [branches])
(defrecord Elsif [test body])

(defn braces
[m]
(cons 'finish (mapcat id m)))

(defmacro c
[& exprs]
(rewrite `(finish ~@exprs)
[#{'else} _, #{'if} _, seq? test, map? body]
[(Elsif. `(do ~@test) (braces body))]

[#{'if} _, seq? test, map? t]
[(Cond. [`(do ~@test) (braces t)])]

[(a Cond) cond, (a Elsif) elsif]
[(update cond :branches conj (:test elsif) (:body elsif))]

[(a Cond) cond, #{'else} _, map? body]
[(update cond :branches conj :else (braces body))]
...
((a Cond) c) `(cond ~@(:branches c))))
person=> (c
x = 3;
if (x == 2) {
println("two");
} else if (x == 3) {
println("yes!");
} else {
println("nope");
}
)
yes!

A single eyelash detaches from the nook of your watch, and drifts into the air, smoldering gently. Facet effects near at a payment.

Martín stares carefully at your REPL, as if there would possibly be one thing immoral with it, and never the arena. “Those are… plan literals,” he states, as if unsure.

“They are, aren’t they?” You compromise, contented.

“They’re now not… ordered maps… are they?”

You would possibly perchance perchance furthermore barely aid from cackling. “They are, up to sixteen terms.”

While Martín sputters, you concentrate on including one other else if clause, and realize that your spell requires a more transgressive magic. Double-take a look at your keybindings, clap twice, and trace a protective ward upon the tabletop. What you are about to complete is now not precisely unfriendly, nonetheless would possibly perchance piss one thing off.

(defn spaced-sym
[x]
(when (image? x)
(let [parts (str/split (name x) #" ")]
(when (< 1 (count parts))
(map symbol parts)))))

(defmacro c
[& exprs]
(rewrite `(do ~@exprs)
[spaced-sym s] (spaced-sym s)
...
['#{return ;} _] nil))

Martín is asking something pedestrian about the reader. “Line terminators are a social construct,” you offer, gently, because information is often uncomfortable. “As are spaces. It’s… actually in the spec.” You wonder, not for the first time, why Dr. Judith Butler took such an interest in chairing the ISO 10646 working group. She must have had her reasons.

“All that is left is the for loop itself.” A nontrivial construct, you realize, and prepare to weave another function. Initialization, iteration, termination, evaluation. Trace the sigils in the air and give them form.

(defn gen-for
[exprs body]
(let [[[var _ init] test change] (remove '#{(;)} (partition-by '#{;} exprs))
body (mapcat identity body)]
`(loop([~var ~init
ret# nil]
if (~@test) {
recur(do(~@change), do(~@body))
} ~'else {
~'return ret#
}))))

(defmacro c
[& exprs]
(rewrite `(do ~@exprs)
[#{'for} _, seq? expr, map? body] (gen-for expr body)

[spaced-sym s] (spaced-sym s)

[#{'else} _, #{'if} _, seq? test, map? body]
[(Elsif. `(do ~@test) (braces body))]

[#{'if} _, seq? test, map? t]
[(Cond. [`(do ~@test) (braces t)])]

[(a Cond) cond, (a Elsif) elsif]
[(update cond :branches conj (:test elsif) (:body elsif))]

[(a Cond) cond, #{'else} _, map? body]
[(update cond :branches conj :else (braces body))]

[symbol? fun, seq? args] [(FnCall. fun args)]
[any? a, infix f, any? b] [(FnCall. (infix f) [a b])]
(postfix-sym x) (postfix-sym x)

[symbol? var, #{'=} _, any? rhs, & more]
[`(let [~var ~rhs] ~@more)]

((a FnCall) fc) (cons (:fun fc) (:args fc))
((a Cond) c) `(cond ~@(:branches c))
['#{return ;} _] nil))

“Martín,” you whisper. Dust shimmers in columns above your parentheses. “We are ready now. Would you like to see?”

user=> (c
for (i = 1 ; i < 101 ; i++) {
if (i % 15 == 0) {
println("FizzBuzz");
} elseif (i % 3 == 0) {
println("Fizz");
} elseif (i % 5 == 0) {
println("Buzz");
} else {
println(i);
};
}
)
1
2
Fizz
4
Buzz
Fizz
...

Because the numbers scamper upwards alongside the screen screen, Martín closes his eyes and releases a long, drained breath. One hand rests on the waxed pine of the convention room’s desk; the opposite supports his temple. “I’m recommending rep hire needless to direct, nonetheless…” He leans in, and speaks more quietly. “Attain you in actuality ponder you’d be happy right here?”

You’re blessed with time and energy, and desire now not root in melancholy soil. Thank him, elevate your seed-fly, and let your ft dangle gently as you shuffle away.

With sincerest thanks to C. Scott Andreas, André Arko, David Ascher, Mike Bernstein, Lita Cho, Nicole Forsgren, Coda Hale, Michael Handler, Marc Hedlund, Ben Linsay, Caitie McCaffrey, Dan McKinley, Greg Poirier, Marco Rogers, Kelly Shortridge, Tasha, and Leif Walsh.

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