弱类型、强类型、动态类型、静态类型

> "1"+2
‘12‘

>>> "1"+2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: cannot concatenate ‘str‘ and ‘int‘ objects

>>> a = 1
>>> type(a)
<type ‘int‘>
>>> a = "s"
>>> type(a)
<type ‘str‘>

Prelude> let a = "123" :: Int

<interactive>:2:9:
    Couldn‘t match expected type `Int‘ with actual type `[Char]‘
    In the expression: "123" :: Int
    In an equation for `a‘: a = "123" :: Int