Re: [Haskell-cafe] Word rigid in "`a' is a rigid type variable..."

I think that more intuitive/understandable would be something like

'b' has too rigid type for 'a' ...

At least, that is what I have to tell myself when I encounter this issue

I don't think this is quite correct. As I'm a daily Java programmer, one thing that really troubled me was to think as `a' being something like `Object', but it is wrong. The `a' really means that the client of the function can define the type it wants, and be precise. I guess it's easier to see this in the value (result) of a function: "f :: a -> b" is a function that takes any value and produces any value the user wants, i.e. I can take an Int out of it, or a Double, or a String, or a Foo, or a Bar. That's a huge difference between Java's "Object f(Object a)" (a better comparison would be with " B f(A a);", I guess). I'm diverging a bit, but what I want to say is that there is no way to tell that the type of "b" is "too rigid" for the type `a' , because the `a' can be anything, even the exact type of "b".