remove example usage of from_str in error docs

Fixes #24185

Author: steveklabnik

src/doc/trpl/error-handling.md

@@ -20,18 +20,18 @@ panic. A *failure* is an error that can be recovered from in some way. A
 *panic* is an error that cannot be recovered from.
 
 What do we mean by "recover"? Well, in most cases, the possibility of an error
-is expected. For example, consider the `from_str` function:
+is expected. For example, consider the `parse` function:
 
-```{rust,ignore}
-from_str("5");
+```ignore
+"5".parse();
 ```
 
-This function takes a string argument and converts it into another type. But
-because it's a string, you can't be sure that the conversion actually works.
-For example, what should this convert to?
+This method converts a string into another type. But because it's a string, you
+can't be sure that the conversion actually works. For example, what should this
+convert to?
 
-```{rust,ignore}
-from_str("hello5world");
+```ignore
+"hello5world".parse();
 ```
 
 This won't work. So we know that this function will only work properly for some
@@ -40,7 +40,8 @@ inputs. It's expected behavior. We call this kind of error a *failure*.
 On the other hand, sometimes, there are errors that are unexpected, or which
 we cannot recover from. A classic example is an `assert!`:
 
-```{rust,ignore}
+```rust
+# let x = 5;
 assert!(x == 5);
 ```
 
@@ -119,17 +120,19 @@ Rust calls these sorts of errors *panics*.
 # Handling errors with `Option` and `Result`
 
 The simplest way to indicate that a function may fail is to use the `Option<T>`
-type. Remember our `from_str()` example? Here's its type signature:
+type. For example, the `find` method on strings attempts to find a pattern
+in a string, and returns an `Option`:
 
-```{rust,ignore}
-pub fn from_str<A: FromStr>(s: &str) -> Option<A>
+```rust
+let s = "foo";
+
+assert_eq!(s.find('f'), Some(0));
+assert_eq!(s.find('z'), None);
 ```
 
-`from_str()` returns an `Option<A>`. If the conversion succeeds, it will return
-`Some(value)`, and if it fails, it will return `None`.
 
 This is appropriate for the simplest of cases, but doesn't give us a lot of
-information in the failure case. What if we wanted to know _why_ the conversion
+information in the failure case. What if we wanted to know _why_ the function
 failed? For this, we can use the `Result<T, E>` type. It looks like this:
 
 ```rust