TypeScript Error Handling Patterns

Errors should also be typed.

      ## Result pattern
      ```ts
      type Ok<T> = { ok: true; value: T };
      type Err = { ok: false; error: string };
      type Result<T> = Ok<T> | Err;
      ```
      
      ## Function returning Result
      ```ts
      function parseNum(s: string): Result<number> {
        const n = Number(s);
        return isNaN(n) ? { ok: false, error: "Not a number" } : { ok: true, value: n };
      }
      ```
      
      ## Use it
      ```ts
      const r = parseNum("10");
      if (r.ok) {
        console.log(r.value);
      } else {
        console.error(r.error);
      }
      ```
      
      ## Graph
      ```mermaid
      flowchart TD
        A[Function] --> B{ok?}
        B -->|Yes| C[Value]
        B -->|No| D[Error]
      ```
      
      ## Remember
      - Types can model success and failure
      - Reduces runtime surprises