mostly looks like incomplete invocations of the format! macro.

$ cargo install wordlet
...
   Compiling wordlet v0.2.0
error: there is no argument named `answer`
   --> /home/crinklywrappr/.cargo/registry/src/github.com-1ecc6299db9ec823/wordlet-0.2.0/src/ui.rs:249:49
    |
249 |             format!("Game over! The answer was '{answer}'. Press any key to exit.")
    |                                                 ^^^^^^^^

error: there is no argument named `letter`
   --> /home/crinklywrappr/.cargo/registry/src/github.com-1ecc6299db9ec823/wordlet-0.2.0/src/ui.rs:253:64
    |
253 |                 format!("Does not include the required letter '{letter}'")
    |                                                                ^^^^^^^^

error: there is no argument named `ch`
   --> /home/crinklywrappr/.cargo/registry/src/github.com-1ecc6299db9ec823/wordlet-0.2.0/src/ui.rs:260:35
    |
260 |                     _ => format!("{ch}th"),
    |                                   ^^^^

error: there is no argument named `number`
   --> /home/crinklywrappr/.cargo/registry/src/github.com-1ecc6299db9ec823/wordlet-0.2.0/src/ui.rs:262:30
    |
262 |                 format!("The {number} letter must be '{ch}'")
    |                              ^^^^^^^^

error: there is no argument named `ch`
   --> /home/crinklywrappr/.cargo/registry/src/github.com-1ecc6299db9ec823/wordlet-0.2.0/src/ui.rs:262:55
    |
262 |                 format!("The {number} letter must be '{ch}'")
    |                                                       ^^^^

error: there is no argument named `le`
   --> /home/crinklywrappr/.cargo/registry/src/github.com-1ecc6299db9ec823/wordlet-0.2.0/src/ui.rs:349:26
    |
349 |         true => format!("{le} "),
    |                          ^^^^

error: failed to compile `wordlet v0.2.0`, intermediate artifacts can be found at `/tmp/cargo-installO2YmIV`

Caused by:
  could not compile `wordlet` due to 6 previous errors
Exception: cargo exited with 101
[tty 19], line 1: cargo install wordlet