#preorder traversal

[sufiblackmamba]

[bigcats-birds-and-books]

y'all i am getting SO much mileage out of my "book buying ban except preorders" caveat :)

[cozybao]

🏡 my zine "what if we were…" is part of a series of 4 risograph zines by nonbinary sapphic artists. it traverses love found in tangible objects we hold dear to us 🍎

this zine was created with photographs and scans of my collection of anik-anik, trinkets, and ephemera over the years. 🏡

preorders are open for the 2nd week of komiket pride (jun 14-16)! 🍀

🍏 us preorders - kittybug press

🍊 ph preorders - cloud burst press

[bearpillowmonster]

Epic Mickey: Rebrushed

I'm an Epic Mickey stan, I would've bought this whether I played it or not, just to support it because I've always wanted more. (mainly, for Oswald!) But so much was planned for this franchise, including a movie and an Epic Donald spinoff.

CHANGES

Looking at this is night and day especially for a dark setting. The graphics weren't bad on the Wii, they were just, well, on the Wii. (which ran at max 720p) And while that's still feasible, it's so nice to see everything smoothed out and relit. They didn't have to go as far as messing with the actual fidelity of it or the custscenes but they make it known what a movie it would've been and we lost boys.

The addition of sprinting, dashing and butt stomping is really what this game needed because the first Epic Mickey was a Wii exclusive and I loved playing it when I first got into it but I found it had faded since then. I came back maybe a year or two ago to try and play it again and I just couldn't bring myself to. I like platforming and the platforming in this game sucked, it wouldn't control right, I felt like I was jumping in a straight line, like barely any momentum. It wasn't quite there for something you do a lot of. And if you fall in the thinner, there's very seldom a platform to catch you so dying sets you back and then you had to walk back so sprinting is just a complete clutch.

You also had aiming to deal with as far as the Wii remote- This review is for the Switch version, yeah, I knew that it would run a little worse than the other consoles but now I have the experience to talk about specifics and I wanted to play it on the go. The darkness I mentioned can be adjusted, not just in brightness but in color and style for color deficiency. You cannot shake the joycon to spin.

There is a choice to use motion controls when you're spraying but that's the only time it comes up, you already have to have the button pressed down and even then you can just use the analog stick, it's really good either way, no complaints. You can also set it if you're standing still and press the down arrow. The framerate…could dip and there was a time or two where it'd get stuck, the load times can be long (but you don't see a loading screen often) it's just weird to me that the game is a remaster of a game from 2010 and actually has the biggest file size on my Switch and even with all that size, has longer loading screens than comparable titles like Super Mario Odyssey.

And this is especially important for this game because you sometimes have to traverse back and forth between Ostown and Mean Street and whatever to get the side quests done (and sometimes main) and every time you have to speedrun the same pathway level (projector) to get there and each time you jump in or out is a loading screen. Seeing as this is labelled as a remake and not just a remaster, they very well could've made a fast travel. There were some instances like that where the sequel had the feature that I wanted and was hoping that it'd be updated in here like so many remaksters are doing now, Last of Us and Horizon for example.

The one thing that did carry over is that you've probably seen the different skins that you get with either preorder or purchase, there are a few unlockable ones as well. They fit well with the 2.5D levels (Brave Little Tailor for 30s cartoons, Steamboat for 20s). There is a photo mode, it's not as customized in the 2D levels but I definitely had fun with it if you can't tell.

It's the same game but it's not one-to-one, for example, the locations of the power boxes are different in Os-Town, scenes like this look different.

Which is a downgrade in my eyes but some of them are very neutral, like the health bar

…that's a choice, I guess, there was no real need to change it. It definitely makes things more textured and seem a little less rough, look at this platform where you find Pete Pan.

Sometimes more detailed and lush, but sometimes it takes from the scene. Little stuff like goo dripping from the ceiling removed, sometimes it's the overall colors and vibes of a level to either lighten or darken. I can't say whether I like one or the other totally more.

THE GAME

Let's talk about the meat because it's 60$ so I'm going to treat it like it as if it was a brand new game, plus I never reviewed the original and I don't talk about it enough so here we go. I'll cover thinner mode in some other post, this is more or less hero mode.

It's a reasonable amount of hours and honestly time as been gracious to it, whether it be the growing cult status or the fact that it's on other consoles other than the Wii because while the combat still leaves a little to be desired, the gameplay overall is a lot more refined in my eyes.

There are times where your paint can't reach an item, it's not a bad limitation but still in sight, it tells you what's reachable by turning green. But this is especially precise and annoying for the ending with the bloticles. I don't get what it is with games and popping bubbles.

Oswald is in this a lot less than I remember, I always thought of him as making mischief for a level but he kind of shows up just to show you your end goal. Towards the second half he appears a lot more though. It's kind of cool how it's all a Alice Through The Looking Glass type thing and Oswald is the White Rabbit. And all things forgotten, Atlantis, Tron…no Black Cauldron (which fits perfectly) and no Treasure Planet though everything that is popular is all mechanical, an artificial imitation and the way Smee is colored makes it look like the concept art, all inverted from the way we know and it's just-

I really like the idea of having different endings correlating to how you played. When I first played this, I tried to hundred percent it first round and paint absolutely every nook and collect every item and to be honest, I found myself doing a lot of the same stuff I did when I started, it's funny, I have the same thought processes but I've come to the conclusion that if I waste my time on just one collectible, it won't be as fun and I won't want to play it anymore and it's been this long so let me finish it. But there are obvious rewards for either path, one of the first I could tell was having a gremlin in a catapult and a chest on the switch. Remove the chest and it launches the gremlin, remove the gremlin and it locks the chest. There are times you can just thinner brush most things and it'll show a negative outlook on the world itself. You can either clean up your mess with paint or take out the trash and destroy it like it never happened.

There are a lot of things to collect and I had fun just looking in every corner though I found that they seem kind of half-and-half, some going by the wayside like the pins and some being cool like the concept art.

[beansproutsong]

[Proxy / Group Order] Love and Deepspace

Paperfold Tmall just added some new goods on their website. Early bird pre order will be accepted until 27th May.

Line up:

Veiled Whisper

Can badges: 600JPY

Standee: 1800JPY

Film strip keychain: 1200JPY 

Heartbeat Ripples: 

Can badges: 500JPY 

Collota (acrylic block): 2100JPY

Shikishi: 1080JPY

Traversing deepspace

Can badges: 500JPY 

Acrylic standee: 1500JPY

Movie Time series

Chibi Acrylic standee: 1080JPY 

Pouch: 1080JPY 

Cassette keychain: 1300JPY 

Memo + acrylic stick: 900JPY

About shipping,

Currently paperfold do not specify the exact shipping date, but I assure you this is quite normal for CN preorder. Some of them can take up to 90 days (3 months). The rafayel birthday goods has not been shipped yet

DM me here or at my twitter (angelic1408) to place your order

[sonicthetarot]

SONIC THE TAROT Card Previews #11

Today's previews are for the Suit of Pentacles' Five of Pentacles, Six of Pentacles, Seven of Pentacles, and Eight of Pentacles! See their guidebook entries below, and check out our website for more and our storefront to preorder a copy!

Five of Pentacles (Eclipse Cannon)

The doomsday device lurking on the Space Colony ARK, the Eclipse Cannon’s ruin embodies the Five of Pentacles. Originally created to fend off the Black Arms, it became one of the few legacies left from Gerald’s fall from grace, with its targets instead set on devastating the Earth. As such, the Eclipse Canon—and all of Project SHADOW—became a scandalous secret for the United Federation and G.U.N., intended to be locked away for good.

Despite the dangers of the Eclipse Cannon, the Five of Pentacles reversed results in some positive outcomes for its eventual reveal. Eggman’s plot to take over the world results in Shadow regaining consciousness, embittered and haunted by his own mind. However, learning the truth of his friend Maria’s final words—triggered only through the interactions with Sonic, Amy, and their other friends due to the threat—changed Shadow for the better, allowing him to let go of his vengeance and work on protecting the Earth instead.

The Five of Pentacles destroys all it touches, but what remains in the aftermath may still kindle positive growth.

Upright Keywords: ruin, hardship, alienation, scandal

Reversed Keywords: positive change, recovery, forgiveness, letting go

Six of Pentacles (Item Box)

Scattered across the world, Item Boxes present those who break them with gifts. As the Six of Pentacles, they share their powers—ranging from invincibility, speed, and even extra lives—with Sonic and friends when they most need support. With these powerups, certain obstacles like spike pits become less threatening during the traversal of zones.

Not all Item Box gifts are a blessing, such as those found in the Six of Pentacles reversed. Powerups like the Eggman Mark are not as generous as they seem, causing damage to those that take them instead of helping. Additionally, certain Item Boxes during competitive games between Sonic and his friends, like the Fireball, directly hinder rivals to allow the user victory.

The Six of Pentacles is generous indeed, but their gifts may not be what you want or seek.

Upright Keywords: generosity, abundance, sharing, gifts

Reversed Keywords: abuse of power, with strings attached, malice, inequality

Seven of Pentacles (Chaos Emeralds)

An ancient array of gemstones from beyond the stars and the Seven of Pentacles, the Chaos Emeralds usually appear at the culmination of Sonic’s adventures. Embodying the ideals of those who possess them, having all seven is needed to enter and sustain a Super State, such as Super Sonic. However, the Chaos Emeralds almost always scatter once the given mission is complete, retiring until ready to be discovered again.

As often as they’re harnessed for good, the Seven of Pentacles reversed showcases when the Chaos Emeralds are used for sinister purposes. Eggman needed all seven to make the Perfect Chaos, but his lack of foresight resulted in Chaos rampaging out of control. Additionally, potential futures for Shadow see him losing focus on his true identity and weaponizing the Chaos Emeralds to conquer Earth, space, or somewhere in between.

The Seven of Pentacles cultivates perseverance beyond measure, but using their power in frustration is ill advised.

Upright Keywords: culmination, perseverance, manifestation, nearing conclusion

Reversed Keywords: lack of foresight, poor planning, lost focus, regression

Eight of Pentacles (Piko Piko Hammer)

Amy’s weapon of choice, the Piko Piko Hammer is a fierce opponent in the right hands. Great mastery of skill represents the Eight of Pentacles, and Amy has done everything with the Piko Piko Hammer, from flinging herself into the air in a frontflip to denting the cabin of the Mirage Express. The Piko Piko Hammer rewards Amy with a level of confidence that allows her to stand toe-to-toe with her more overtly supernatural friends.

This confidence can quickly turn into brashness when the Eight of Pentacles is reversed. Amy has been known to raise her hammer in anger against her friends for perceived carelessness, such as when Sonic missed his “date” with her during the Black Knight incident. Additionally, not every Piko Piko Hammer is built equally: her hammer during the Chaos incident needed to be upgraded to be stronger and perform her spin attacks, while the backup one during her birthday party initially broke after one swing.

The Eight of Pentacles has both high craftsmanship and a skill barrier, but needs to be used with a level head.

Upright Keywords: high reputation, mastery, bringing results, success

Reversed Keywords: brashness, aggressiveness, poor results, overestimation of skill

CHECK OUT OUR WEBSITE AND PREORDER NOW!

[black-arcana]

WITHIN TEMPTATION To Release 'Worlds Collide Tour: Live In Amsterdam' Live Album And DVD/Blu-Ray

Ahead of WITHIN TEMPTATION's upcoming tour, fans can prepare for the spectacle by reliving the adrenaline-pumping excitement of 2022's "Worlds Collide" run from the comfort of their homes, as the band's remarkable show at Ziggo Dome in Amsterdam on November 29, 2022, will be available on vinyl, CD, Blu-ray/DVD and in a special 64-page hardcover artbook on June 21, 2024.

During the "Worlds Collide" tour, WITHIN TEMPTATION played two sold-out shows in their home country at Ziggo Dome. They were their first-ever headlining shows in Ziggo Dome and a total of 30,000 fans were there to witness the occasion. These shows were captured for posterity and now everyone around the world has the chance to immerse themselves in one of the most iconic performances the band has ever done in their home country.

Few collaborations in WITHIN TEMPTATION's career have ignited as much anticipation as their co-headlining tour with EVANESCENCE did, especially having being postponed four times due to COVID.

As soon as the world reopened in 2022, the "Worlds Collide" tour finally took place. Over the course of over four weeks, the tour traversed 17 cities across Europe, delivering a total of 19 performances.

For this tour, WITHIN TEMPTATION and EVANESCENCE saw an amazing amount of over 200,000 tickets sold, 7703 kilometers traveled, eight tour buses serving as mobile homes for the artists and crew, twelve trailers loaded with the gear to fuel the spectacle, and a dedicated team of over 80 experienced individuals whose tireless efforts ensured that every aspect of the tour ran seamlessly.

Experience the audio and visual spectacle that was brought to life in Ziggo Dome on November 29, 2022 now. Preorder your copy in the official WITHIN TEMPTATION music store.

Last month, WITHIN TEMPTATION released the official music video for their newest single, "A Fool's Parade", featuring Ukrainian producer and vocalist Alex Yarmak. All royalties from the new single will be donated to Music Saves UA for the duration of the Russia-Ukraine war.

According to a press release from WITHIN TEMPTATION's publicist, "A Fool's Parade" "showcases the band's commitment to raising awareness of Ukraine's ongoing battle against Russia's invasion. The song itself serves as a condemnation of Russia's deceitful actions and sheds light on the harsh realities faced by Ukraine. WITHIN TEMPTATION remains steadfast in their support for Ukraine, with involvement in initiatives such as the Ukraine Aid OPS foundation, advocating for more much-needed solidarity."

Recorded amidst the streets of Kyiv with renowned Ukrainian video director Indy Hait, the music video for "A Fool's Parade" captures WITHIN TEMPTATION frontwoman Sharon Den Adel at important Ukrainian landmarks.

Released last October, WITHIN TEMPTATION's latest album, "Bleed Out", signifies a bold leap forward for the band. From contemporary, hard-hitting, and djenty riffs to soaring melodies displaying their symphonic roots, WITHIN TEMPTATION has created a sonic journey that fuses diverse musical styles and thought-provoking themes. This is an album that is as epic as it is unflinchingly outspoken, and now more than ever, this is a band who isn't afraid to make a stand on issues the members care about.

Since the start of the war in Ukraine, WITHIN TEMPTATION have shifted their focus from writing about personal emotions and societal subjects to tackling global injustices and reflecting the tumultuous state of the world in a way that other artists seem unable or unwilling to do.

While songs such as "Wireless" and "We Go To War" examine the authoritarian aggression on display in Ukraine and other warzones, the title track itself addresses the plight of women fighting for their rights in Iran after the murder of Mahsa Amini.

The album also grapples with the complex issues around a woman's right to choose in single "Don't Pray For Me" and throughout, this impassioned and political focus is reflected in the intensity and heaviness of the music. Embracing a new era of musical exploration and lyrical depth, WITHIN TEMPTATION have pushed boundaries and showcased their artistic evolution, delivering a fist-in-the-air proclamation of both their moral convictions and their fearless approach to music.

[astrophelbkdkbk]

✩₊˚.⋆☾⋆⁺₊✧ COVER REVEAL✧₊⁺⋆☾⋆.˚₊✩

We've traversed through the cosmos and have returned with this gorgeous cover designed by the amazing @esparafuso! Preorders open June 29th at 11am EDT.

[fruitstickerr]

hello and i hope you're all doing alright 🩷 just want to share some things i've been up to lately:

i recently held a talk on collecting trinkets and the importance of having physical reminders of a life well-lived in our fast-paced digital age! i take from bits and pieces of linguistics and psychology in the filipino context. the talk can be found here if you're interested in watching! ♡

i also made a zine, which is part of a series of 4 risograph zines by nonbinary sapphic artists. it traverses love found in tangible objects we hold dear to us. previews can be found here, and ph / us preorders are ongoing ♡

last week i also took a talent exam to shift to an arts course! i haven't been feeling fulfilled in my course and think this is the path i want to take. it's been nerve-wracking, but i'm trying my best to keep going.

i've also been reevaluating my relationship with the internet and how it's affected my creative practice. i've been thinking of ways to ignite my passion to learn and create without getting stuck in the algorithmic echochamber of social media.

how have you been doing? feel free to share or ask me anything in my ask! i hope you enjoy my little blog and the things i scan-they're intimate snapshots of my interests and life, so i hope you find joy in them! i hope your day is warm and full of love 🩷

[finishinglinepress]

NEW FROM FINISHING LINE PRESS: Post-Traumatic Poetry by Mackenzie Rose

On SALE now! Pre-order Price Guarantee: https://www.finishinglinepress.com/product/post-traumatic-poetry-by-mackenzie-rose/

Post-Traumatic Poetry is at once deeply personal and frighteningly universal. Mackenzie Rose‘s collection of #poems shares her story from being a young woman in an abusive relationship to becoming a #domestic #violence #survivor. Her poems take the reader through her first glimpses of her partner’s narcissism and gas-lighting to the moment he tried to kill her. They untangle her medical trauma and find her traversing the world with a new identity while learning to understand her physical and emotional scars.

Mackenzie Rose is a survivor. On August 26, 2017, only two days after her 28th birthday, the man with whom she shared a home plunged a chef’s knife into her throat, past her tongue, and through the roof of her mouth. After eight days of recovery in the hospital, Mackenzie re-entered the world with a limited ability to speak, a PEG feeding tube, and PTSD (post-traumatic stress disorder). After relentless therapies, she began to reclaim some semblance of normality and retrained her voice to carry her new narrative. Mackenzie is a professor of Communications and English at Shenandoah University and a PhD student of trauma studies at Virginia Polytechnic Institute and State University. She can be found speaking at public functions about destigmatizing trauma. With her dog, Bertie, Mackenzie Rose frequently escapes to the beautiful wilderness of the Shenandoah National Park to recharge and find peace in Nature’s healing qualities.

For more information, please visit rosestorytelling.com.

Please share/repost #flpauthor #preorder #AwesomeCoverArt #read #poems #literature #poetry

[leetcode1]

LEETCODE PROBLEMS 1-100 . C++ SOLUTIONS

Arrays and Two Pointers   1. Two Sum – Use hashmap to find complement in one pass.   26. Remove Duplicates from Sorted Array – Use two pointers to overwrite duplicates.   27. Remove Element – Shift non-target values to front with a write pointer.   80. Remove Duplicates II – Like #26 but allow at most two duplicates.   88. Merge Sorted Array – Merge in-place from the end using two pointers.   283. Move Zeroes – Shift non-zero values forward; fill the rest with zeros.

Sliding Window   3. Longest Substring Without Repeating Characters – Use hashmap and sliding window.   76. Minimum Window Substring – Track char frequency with two maps and a moving window.

Binary Search and Sorted Arrays   33. Search in Rotated Sorted Array – Modified binary search with pivot logic.   34. Find First and Last Position of Element – Binary search for left and right bounds.   35. Search Insert Position – Standard binary search for target or insertion point.   74. Search a 2D Matrix – Binary search treating matrix as a flat array.   81. Search in Rotated Sorted Array II – Extend #33 to handle duplicates.

Subarray Sums and Prefix Logic   53. Maximum Subarray – Kadane’s algorithm to track max current sum.   121. Best Time to Buy and Sell Stock – Track min price and update max profit.

Linked Lists   2. Add Two Numbers – Traverse two lists and simulate digit-by-digit addition.   19. Remove N-th Node From End – Use two pointers with a gap of n.   21. Merge Two Sorted Lists – Recursively or iteratively merge nodes.   23. Merge k Sorted Lists – Use min heap or divide-and-conquer merges.   24. Swap Nodes in Pairs – Recursively swap adjacent nodes.   25. Reverse Nodes in k-Group – Reverse sublists of size k using recursion.   61. Rotate List – Use length and modulo to rotate and relink.   82. Remove Duplicates II – Use dummy head and skip duplicates.   83. Remove Duplicates I – Traverse and skip repeated values.   86. Partition List – Create two lists based on x and connect them.

Stack   20. Valid Parentheses – Use stack to match open and close brackets.   84. Largest Rectangle in Histogram – Use monotonic stack to calculate max area.

Binary Trees   94. Binary Tree Inorder Traversal – DFS or use stack for in-order traversal.   98. Validate Binary Search Tree – Check value ranges recursively.   100. Same Tree – Compare values and structure recursively.   101. Symmetric Tree – Recursively compare mirrored subtrees.   102. Binary Tree Level Order Traversal – Use queue for BFS.   103. Binary Tree Zigzag Level Order – Modify BFS to alternate direction.   104. Maximum Depth of Binary Tree – DFS recursion to track max depth.   105. Build Tree from Preorder and Inorder – Recursively divide arrays.   106. Build Tree from Inorder and Postorder – Reverse of #105.   110. Balanced Binary Tree – DFS checking subtree heights, return early if unbalanced.

Backtracking   17. Letter Combinations of Phone Number – Map digits to letters and recurse.   22. Generate Parentheses – Use counts of open and close to generate valid strings.   39. Combination Sum – Use DFS to explore sum paths.   40. Combination Sum II – Sort and skip duplicates during recursion.   46. Permutations – Swap elements and recurse.   47. Permutations II – Like #46 but sort and skip duplicate values.   77. Combinations – DFS to select combinations of size k.   78. Subsets – Backtrack by including or excluding elements.   90. Subsets II – Sort and skip duplicates during subset generation.

Dynamic Programming   70. Climbing Stairs – DP similar to Fibonacci sequence.   198. House Robber – Track max value including or excluding current house.

Math and Bit Manipulation   136. Single Number – XOR all values to isolate the single one.   169. Majority Element – Use Boyer-Moore voting algorithm.

Hashing and Frequency Maps   49. Group Anagrams – Sort characters and group in hashmap.   128. Longest Consecutive Sequence – Use set to expand sequences.   242. Valid Anagram – Count characters using map or array.

Matrix and Miscellaneous   11. Container With Most Water – Two pointers moving inward.   42. Trapping Rain Water – Track left and right max heights with two pointers.   54. Spiral Matrix – Traverse matrix layer by layer.   73. Set Matrix Zeroes – Use first row and column as markers.

This version is 4446 characters long. Let me know if you want any part turned into code templates, tables, or formatted for PDF or Markdown.

[programmingandengineering]

CS 202 Homework 2 – Binary Search Trees

Question 1 – 20 points (6 points) Give the prefix, infix, and postfix expressions obtained by preorder, inorder, and postorder traversals, respectively, for the expression tree below: (9 points) I​nsert 31, 7, 56, 2, 1, 41, 45, 10, 70, 42, 38, 9 to an empty Binary Search Tree, and then delete 1, 45, 56, 7 in the given order. Show the evolution of the BST after each insertion and deletion…

[ankitcodinghub]

CS2110 - Project 5: Generic Binary Search Tree Solved

Prabhav Gupta, Michael Rodyushkin, Archita Hothur, Rohan Bafna, Matthew Free Contents 1 Overview 2 2 Binary Search Tree Implementation 2 2.1 What is a binary tree? 2 2.2 What is a binary search tree? 2 2.3 What is a preorder traversal? 3 2.4 How will we implement a BST? 3 3 Instructions 5 3.1 General instructions 5 3.2 Functions you need to implement 5 3.3 Functions provided 6 4 Building &…

[javamyblog]

Unveiling Preorder Traversal of Binary Trees

144. Binary Tree Preorder Traversal Given the root of a binary tree, return the preorder traversal of its nodes’ values. Example 1: Input: root = [1,null,2,3] Output: [1,2,3] Example 2: Input: root = [] Output: [] Example 3: Input: root = [1] Output: [1] Constraints: The number of nodes in the tree is in the range [0, 100]. -100 <= Node.val <= 100 In the realm of binary trees,…

[myprogrammingsolver]

Homework 2 – Binary Search Trees Solved

Question 1 – 20 points (6 points) Give the prefix, infix, and postfix expressions obtained by preorder, inorder, and postorder traversals, respectively, for the expression tree below: (9 points) I​nsert 31, 7, 56, 2, 1, 41, 45, 10, 70, 42, 38, 9 to an empty Binary Search Tree, and then delete 1, 45, 56, 7 in the given order. Show the evolution of the BST after each insertion and deletion…

[theohonohan]

Polish Notation and Laziness

I decided to write a parser for Łukasiewicz's parenthesis-free notation, more commonly known as Polish Notation. One of the first Google hits I read suggested that the easiest way to do this is to reverse the expression and decode it as Reverse Polish Notation. Parsing RPN with a stack is a very easy and simplistic solution, so this suggestion is obviously a cop-out. I decided to write a Haskell program instead.

The expression to be parsed looks something like this: \(EKKCprCqrKCpsCqsCApqKrs\)

Upper-case letters are operators and lower-case letters are variables. Polish notation corresponds to a preorder traversal of the syntax tree for the expression. So my Haskell program just reads each character of the expression, from left to right, and builds the tree as it goes along. It's very natural to do this in Haskell, thanks to algebraic data types. Because it's an incremental process, the program can parse truncated expressions. The result, in that case, is a syntax tree with one or more "holes". This is a fairly familiar item in functional programming, and it's a straightforward way of representing the structure of an incomplete expression.

The "reverse it and parse as RPN" approach is clearly unable to make sense of truncated expressions in Polish Notation. What's more, a truncated RPN expression will result in a collection of values rather than a single value with holes. So there's a kind of duality here between Polish and Reverse Polish Notation.

The advantage of RPN is that, evaluating from left to right, every operator can be applied immediately to its operands. This is because the standard RPN parser pushes every operand it encounters onto a stack, and then pops them all off when it encounters an operator. Operators are never stored by the parser. This ability to calculate values immediately means that an RPN parses for arithmetic expressions doesn't have to build a syntax tree. Somebody programming in assembly, in the 1950s or 60s, would have found it laborious to implement such a data structure. In the 70s, though, computer scientists became aware of the choice between strict and lazy evaluation strategies. Along with the invention of algebraic data types (also in the 70s), this altered the significance of Polish and Reverse Polish Notation.

The traditional simple RPN parser is strict or eager: every operator evaluates its arguments at the earliest opportunity. The Haskell parser I wrote is lazy: it builds a syntax tree and only evaluates it when parsing is complete (if at all). A lazy evaluation strategy requires the cabability of storing suspended computations (known as thunks), which is what the syntax tree ADT amounts to. This kind of complexity doesn't play into the typical RPN-based system. It's also possibly to implement a Polish Notation parser that works in an eager way, storing operators on a stack and applying them as soon as their arguments are available. Of course, the outermost operator still won't be applied until the very end. This possibility means that there isn't a necessary connection between Polish Notation and laziness. It's arguably much more natural, though, to build a syntax tree from an expression in Polish Notation than from an expression in Reverse Polish Notation. So, the way I see it, Polish Notation is a spiritual precursor of modern functional programming (along with the lambda calculus and Schönfinkel's combinators) while Reverse Polish Notation is a kind of efficiency hack, intended for use by those who have no choice but to stay close to the metal.

One problem that the simple RPN evaluator avoids is the memory usage that results from creating thunks. Most Polish Notation expressions are extremely short, but the fact remains that, while an eager RPN evaluator uses essentially constant memory, a lazy evaluator builds a data structure of a size proportional to the length of the expression. This hangs around in memory (as a thunk) until we evaluate it. In Haskell, this becomes a serious consideration with the foldl function, which is intended to work on arbitrarily large lists. Haskell's solution is to provide a strict version of foldl called foldl'. foldl' takes one element at a time from the head of the list it is given, and combines it (strictly) with the initial value. As a result, it works like a tail-recursive function as it consumes the list, and uses constant memory.

My Haskell Polish Notation parser.