Monster Arena

A simple game idea leveraging boxes and ASAs

(alt. title: an excuse to make everybody learn a bit of TEAL)

Ewwww why plain TEAL tho?

• Pyteal is syntactically similar to TEAL
• Beaker is better at abstraction, but runs on top of Pyteal
• Familiarizing ourselves with TEAL code is a good thing!
• Ability to read closed source projects
• Ability to write more performant code
• Ideally a mixed approach (like what happens in embedded systems)
• Lines of code ~= money

Exhibit A: First Hackathon advanced challenges

• Lots of room for improvement in the Pyteal compiler!
• From a sample of 12 contracts with glaring issues (dead code, constant expressions being re-computed multiple times, etc.)
• Contestants had to add code to improve compilation
• Tested scored with S(badAP, contestantAP) = 0.2 * Δsize + 0.8 * Δbudget
• Adding just a few lines, two contestants managed to get up to 40 points!

Int 1337

But…

TEAL generalities

• The stack is used to work with every opcode (depth 1000)
• Only two data types: uint64 and byte arrays (4k max.)
• Parameters first, operator at the end (postfix)
• Non-negative integer arithmetic (e.g. 5-4 fails)
• Boxes: bags of bytes for potentially unlimited storage
• Approval / rejection based on top of stack on finishing (or returning)

Some important opcodes

• Branching: bnz s, bz s, b s
• Subroutines: callsub LABEL, retsub
• Operators and logic and conversion: +, -, *, /, &&, ||, !=, ==, <, >, <=, >=, !
• Type conversion: btoi, itob
• Stack manipulation: push[bytes, int] X, pop, dig n, bury n, dup, swap
• Scratchspace: load n, store n
• Transaction data: txn f, txna f
• State access: app_[global, local]_[get, put]
• Box manipulation: box_[create, delete, extract, replace, get, put]
• Errors and logging: assert, err, log

Snippet 1: branching and logic

Snippet 2: Reading from a box

Snippet 3: Local state get/put

Snippet 4: Loop

Monster Arena

• A little game using the blockchain for data storage and rewards
• There’s monsters with the following data: pos_x, pos_y, ASA_id
• Monsters appear anywhere on the playing field
• For the purpose of this example, map unbounded on non-negative ints. (x,y)
• Monsters are stored in a 4k box, max. 170 active monsters (4096/24)
• ASAs should be unique for every monster and minted on the spot
• Monsters can be killed