Liquidity pools in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Liquidity pools

User deposits tokens

↓

Tokens added to pool

↓

Pool holds reserves

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Users trade tokens via pool

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Pool updates reserves

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Users withdraw tokens + fees

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End

Users add tokens to a pool, which holds reserves. Traders swap tokens through the pool, changing reserves. Users can withdraw their share plus fees.

Execution Sample

Blockchain / Solidity

pool = {'tokenA': 1000, 'tokenB': 1000}
user_deposit = {'tokenA': 100, 'tokenB': 100}
pool['tokenA'] += user_deposit['tokenA']
pool['tokenB'] += user_deposit['tokenB']
print(pool)

This code shows a user adding tokens to a liquidity pool, increasing the pool's reserves.

Execution Table

Step	Action	Pool tokenA	Pool tokenB	Output
1	Initial pool reserves	1000	1000	{'tokenA': 1000, 'tokenB': 1000}
2	User deposits 100 tokenA	1100	1000	Updated tokenA reserve
3	User deposits 100 tokenB	1100	1100	Updated tokenB reserve
4	Print pool state	1100	1100	{'tokenA': 1100, 'tokenB': 1100}

💡 User deposit added, pool reserves updated, final pool state printed.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
pool['tokenA']	1000	1100	1100	1100
pool['tokenB']	1000	1000	1100	1100

Key Moments - 2 Insights

Why does the pool's tokenA reserve increase after the user deposit?

Because the user adds 100 tokenA to the pool, increasing the pool's tokenA reserve from 1000 to 1100 as shown in step 2 of the execution table.

Does the pool update both tokens at the same time?

No, the pool updates tokenA first (step 2), then tokenB (step 3), reflecting the separate deposit actions.

Visual Quiz - 3 Questions

Look at the execution table, what is the pool's tokenB reserve after step 2?

A 1000

B 1100

C 900

D 1200

💡 Hint

Check the 'Pool tokenB' column at step 2 in the execution table.

At which step does the pool's tokenA reserve become 1100?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Pool tokenA' column in the execution table.

If the user deposited 200 tokenB instead of 100, what would be the pool's tokenB reserve after step 3?

A 1100

B 1300

C 1200

D 1400

💡 Hint

Add 200 to the initial 1000 tokenB reserve shown in the variable tracker.

Concept Snapshot

Liquidity pools hold token reserves supplied by users.
Users deposit tokens, increasing pool reserves.
Traders swap tokens via the pool, changing reserves.
Users withdraw tokens plus fees earned.
Pool reserves update step-by-step with deposits and trades.

Full Transcript

Liquidity pools are smart contracts holding tokens from users. Users deposit tokens, which increases the pool's reserves. Traders swap tokens through the pool, changing the amounts held. Users can later withdraw their tokens plus fees earned from trades. In the example, a pool starts with 1000 tokens each of tokenA and tokenB. A user deposits 100 tokens of each. The pool's reserves update step-by-step, first tokenA then tokenB, ending with 1100 tokens each. This process is shown in the execution table and variable tracker. Key moments include understanding how deposits increase reserves and that tokens update separately. The visual quiz checks understanding of these steps. The snapshot summarizes the main points about liquidity pools and their token reserve updates.