问题
in most articles about Haskell you'll find a statement like "Data in Haskell is immutable". I don't quite understand why. For example:
let a = 123
let a = 456
in the main method works. I just changed the data of a from 123 to 456. What am I missing? It's probably a stupid mistake in my train of thought :/
Have a good day!
回答1:
Actually, a hasn't changed. Try this in ghci to see:
> a = 123
> action = print a
> a = 456
> action
123
Compare with a language that has mutable variables, e.g. python:
>>> a = 123
>>> def action(): print a
...
>>> a = 456
>>> action()
456
来源：https://stackoverflow.com/questions/44406434/haskell-what-is-immutable-data