add quadratic_vote example showcasing library packages

Author: mohammadfawaz

.gitignore

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 .idea/
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quadratic_vote/README.md

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+# Quadratic Vote
+
+## Summary
+
+`quadratic_vote` is a governance example that demonstrates Leo **library packages**.
+
+Two reusable libraries handle all the math:
+
+| Package | Kind | What it provides |
+|---------|------|-----------------|
+| `sqrt_math` | library | `isqrt` — integer square root via Newton's method |
+| `vote_math` | library | QV weights, credit costs, voter profiles (depends on `sqrt_math`) |
+| `governance.aleo` | program | Private vote records, proposal outcome checks |
+
+Under **Quadratic Voting (QV)**, a participant's vote weight equals ⌊√(token\_balance)⌋ and
+casting *k* votes costs *k²* credits.  This makes influence grow with the square root of
+wealth rather than linearly — fairer to smaller holders.
+
+| Token balance | Vote weight |
+|---------------|-------------|
+| 1             | 1           |
+| 100           | 10          |
+| 225           | 15          |
+| 1 000         | 31          |
+| 10 000        | 100 (cap)   |
+
+This example is inspired by the [Quadratic Voting](https://en.wikipedia.org/wiki/Quadratic_voting)
+mechanism used in decentralised governance systems such as Gitcoin Grants.
+
+## Noteworthy Features
+
+**Library packages** — `sqrt_math` and `vote_math` are pure libraries: they compile to
+reusable bytecode and are never deployed to the network on their own.
+
+**Library submodules** — each extra `.leo` file under `src/` becomes a named module.  No
+declaration is needed; the filename is the module name.  Items are accessed as
+`lib_name::module_name::item`.
+
+**Cross-submodule calls within a library** — `vote_math::cost::build_profile` calls
+`vote_math::weight::compute` internally; `sqrt_math::checks::is_perfect_square` calls
+`sqrt_math::newton::isqrt`.
+
+**Cross-library submodule calls** — `vote_math::weight::compute` reaches directly into
+`sqrt_math::newton::isqrt`, demonstrating the full dependency chain
+(`governance → vote_math::cost → vote_math::weight → sqrt_math::newton`).
+
+**Top-level library constants** — `vote_math::MAX_WEIGHT`, `vote_math::MIN_BALANCE`, and
+`sqrt_math::ISQRT_MAX` are defined in each library's `lib.leo` and referenced by name from
+within submodules.
+
+**Library struct export** — `vote_math::cost::VoterProfile` is defined in a submodule (field:
+`weight: u32`) and used directly as a variable type inside `governance.aleo`.
+
+**Private vote receipt** — the `Vote` record is private; the token balance that drove the
+weight computation is never revealed on-chain.
+
+## How to Build
+
+### Option A — clone this repo and build in place
+
+```bash
+cd quadratic_vote
+
+cd sqrt_math  && leo build && cd ..
+cd vote_math  && leo build && cd ..
+cd governance && leo build && cd ..
+```
+
+### Option B — create from scratch with the Leo CLI
+
+```bash
+# Create the two libraries and the program.
+leo new --lib sqrt_math
+leo new --lib vote_math
+leo new governance
+
+# Wire up dependencies.
+cd vote_math  && leo add sqrt_math --local ../sqrt_math && cd ..
+cd governance && leo add sqrt_math --local ../sqrt_math && cd ..
+cd governance && leo add vote_math  --local ../vote_math  && cd ..
+
+# Copy source files, then build.
+cd sqrt_math  && leo build && cd ..
+cd vote_math  && leo build && cd ..
+cd governance && leo build && cd ..
+```
+
+`leo new --lib` creates a library package — `program.json` has no `.aleo` suffix and the
+source lives in `src/lib.leo` instead of `src/main.leo`.  `leo add --local` records the
+dependency in `program.json` and lets the compiler resolve cross-package symbols.
+
+## How to Run
+
+All `leo run` commands are issued from inside the `governance/` directory.
+
+### Cast a vote
+
+A participant's token balance is kept private.  The program derives their QV weight and
+returns a private `Vote` receipt.
+
+```
+leo run cast_vote <proposal_id: field> <token_balance: u32> <approve: bool>
+```
+
+**Alice (1 000 tokens, approval):**
+```bash
+leo run cast_vote 1field 1000u32 true
+```
+
+Output:
+```
+{
+  owner: aleo1...private,
+  proposal_id: 1field.private,
+  weight: 31u32.private,
+  approve: true.private,
+  _nonce: ...group.public
+}
+```
+
+**Bob (225 tokens, rejection):**
+```bash
+leo run cast_vote 1field 225u32 false
+```
+
+**Carol (10 000 tokens — hits the `MAX_WEIGHT` cap of 100):**
+```bash
+leo run cast_vote 1field 10000u32 true
+```
+
+### Query the credit cost of casting votes
+
+```
+leo run qv_cost <votes: u32>
+```
+
+How much does it cost to cast 5 votes?
+
+```bash
+leo run qv_cost 5u32
+# Output: 25u32  (= 5²)
+```
+
+### Check whether a number is a perfect square
+
+```
+leo run has_perfect_sqrt <token_balance: u32>
+```
+
+This function bypasses `vote_math` entirely and calls `sqrt_math::checks::is_perfect_square`
+directly, illustrating that a program can reach any library submodule independently.
+
+```bash
+leo run has_perfect_sqrt 1024u32   # 1024 = 32²  → true
+leo run has_perfect_sqrt 1000u32   # 31² = 961, 32² = 1024  → false
+```
+
+### Check whether a proposal is passing
+
+```
+leo run is_passing <approvals: u32> <rejections: u32>
+```
+
+After tallying Alice (31) + Carol (100) = 131 approvals vs Bob's 15 rejections:
+
+```bash
+leo run is_passing 131u32 15u32
+# Output: true
+```
+
+## Run the full demo
+
+```bash
+bash run.sh
+```
+
+## Project structure
+
+Each library is split into **submodules** — separate `.leo` files under `src/` that are
+automatically discovered by the compiler.  No explicit `module` keyword is needed; the
+filename becomes the module name.
+
+```
+quadratic_vote/
+├── sqrt_math/                   # Library: integer square root
+│   ├── program.json             #   "program": "sqrt_math"  (no .aleo suffix)
+│   └── src/
+│       ├── lib.leo              #   const ISQRT_MAX
+│       ├── newton.leo           #   fn isqrt(n) — Newton's method              [module: newton]
+│       └── checks.leo          #   fn is_perfect_square(n)                    [module: checks]
+│
+├── vote_math/                   # Library: QV weight & cost formulas
+│   ├── program.json             #   depends on sqrt_math
+│   └── src/
+│       ├── lib.leo              #   const MAX_WEIGHT, MIN_BALANCE
+│       ├── weight.leo           #   fn compute(balance), fn is_eligible(balance) [module: weight]
+│       └── cost.leo             #   struct VoterProfile { weight },            [module: cost]
+│                                #   fn credits_for_votes, fn build_profile(balance)
+│
+├── governance/                  # Program: private vote receipts
+│   ├── program.json             #   depends on sqrt_math + vote_math
+│   ├── inputs/governance.in
+│   ├── src/main.leo             #   record Vote
+│   │                            #   fn cast_vote       — uses vote_math::weight + vote_math::cost
+│   │                            #   fn qv_cost         — uses vote_math::cost
+│   │                            #   fn has_perfect_sqrt — uses sqrt_math::checks directly
+│   │                            #   fn is_passing
+│   └── tests/
+│       └── test_governance.leo  #   @test fns covering cast_vote, qv_cost, has_perfect_sqrt,
+│                                #   is_passing (18 test cases)
+│
+├── run.sh
+└── README.md
+```
+
+### Call graph
+
+```
+governance.aleo
+├── vote_math::weight::is_eligible(token_balance)
+│     └── vote_math::MIN_BALANCE                  (top-level lib constant)
+├── vote_math::cost::build_profile(token_balance)
+│     └── vote_math::weight::compute(balance)     (cross-submodule call within vote_math)
+│           ├── sqrt_math::newton::isqrt(n)       (cross-library submodule call)
+│           │     └── sqrt_math::ISQRT_MAX         (top-level lib constant, safety assert)
+│           └── vote_math::MAX_WEIGHT              (top-level lib constant)
+├── vote_math::cost::credits_for_votes(votes)
+└── sqrt_math::checks::is_perfect_square(n)       (direct cross-library submodule call)
+      └── sqrt_math::newton::isqrt(n)              (cross-submodule call within sqrt_math)
+            └── sqrt_math::ISQRT_MAX               (top-level lib constant, safety assert)
+```