Few corrections

weth/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "stylus-hello-world-minimal"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+stylus-sdk = "0.4.1"
+wee_alloc = "0.4.5"
+
+[features]
+export-abi = ["stylus-sdk/export-abi"]
+
+[lib]
+crate-type = ["lib", "cdylib"]
+
+[workspace]

weth/src/lib.rs

@@ -0,0 +1,65 @@
+#![cfg_attr(not(feature = "export-abi"), no_main, no_std)]
+extern crate alloc;
+
+use crate::erc20::{Erc20, Erc20Params};
+use alloc::{string::String, vec::Vec};
+use stylus_sdk::{alloy_primitives::U256, call, msg, prelude::*};
+
+#[global_allocator]
+static ALLOC: wee_alloc::WeeAlloc = wee_alloc::WeeAlloc::INIT;
+
+mod erc20;
+
+struct WethParams;
+
+/// Immutable definitions
+impl Erc20Params for WethParams {
+    const NAME: &'static str = "Wrapped Ether Example";
+    const SYMBOL: &'static str = "WETH";
+    const DECIMALS: u8 = 18;
+}
+
+// The contract
+sol_storage! {
+    #[entrypoint] // Makes Weth the entrypoint
+    struct Weth {
+        #[borrow] // Allows erc20 to access Weth's storage and make calls
+        Erc20<WethParams> erc20;
+    }
+}
+
+// Another contract we'd like to call
+sol_interface! {
+    interface IMath {
+        function sum(uint256[] values) pure returns (string, uint256);
+    }
+}
+
+#[external]
+#[inherit(Erc20<WethParams>)]
+impl Weth {
+    #[payable]
+    pub fn deposit(&mut self) -> Result<(), Vec<u8>> {
+        self.erc20.mint(msg::sender(), msg::value());
+        Ok(())
+    }
+
+    pub fn withdraw(&mut self, amount: U256) -> Result<(), Vec<u8>> {
+        self.erc20.burn(msg::sender(), amount)?;
+
+        // send the user their funds
+        call::transfer_eth(msg::sender(), amount)
+    }
+
+    // sums numbers
+    pub fn sum(values: Vec<U256>) -> Result<(String, U256), Vec<u8>> {
+        Ok(("sum".into(), values.iter().sum()))
+    }
+
+    // calls the sum() method from the interface
+    pub fn sum_with_helper(&self, helper: IMath, values: Vec<U256>) -> Result<U256, Vec<u8>> {
+        let (text, sum) = helper.sum(self, values)?;
+        assert_eq!(&text, "sum");
+        Ok(sum)
+    }
+}