add errors project; fix build in previous session

Author: Byron

Cargo.lock

@@ -1,2 +1,2 @@
 [workspace]
-members = ["./ownership-and-borrowing", "options-and-results"]
+members = ["./ownership-and-borrowing", "options-and-results", "errors"]

Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "errors"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

errors/Cargo.toml

@@ -0,0 +1 @@
+fn main() {}

errors/src/main.rs

@@ -5,10 +5,9 @@ fn add_one_safely(v: u8) -> Result<u8, &'static str> {
 }
 
 fn main() -> Result<(), &'static str> {
-    std::env::args()
-        .is_empty()
+    (std::env::args().len() == 1)
         .then(|| "need two args")
-        .map(Err)
+        .map(Err::<(), _>)
         .transpose()?;
     println!("{}", add_one_safely(255)?);
     Ok(())