What are Haskell's strictness points?

Question

We all know (or should know) that Haskell is lazy by default. Nothing is evaluated until it must be evaluated. So when must something be evaluated? There are points where Haskel

Answer 1

Lazy doesn't mean do nothing. Whenever your program pattern matches a case expression, it evaluates something -- just enough anyway. Otherwise it can't figure out which RHS to use. Don't see any case expressions in your code? Don't worry, the compiler is translating your code to a stripped down form of Haskell where they are hard to avoid using.

For a beginner, a basic rule of thumb is let is lazy, case is less lazy.