Haskell Error - Naked Expression at Top Level

问题

I have the following code:

fib n
    | n == 0  = 0
    | n == 1  = 1
    | n > 1  = fib (n-1) + fib (n-2)

print fib 5

And for some reason, it's throwing an error:

[1 of 1] Compiling Main             ( test.hs, test.o )

test.hs:8:1: Parse error: naked expression at top level

What's going on?

回答1:

You cannot have an expression at the top-level. Haskell program entry point is a main function in Main module. Also print fib 5 calls print with two arguments, you need to do:

main = print $ fib 5

or

main = print (fib 5)

来源：https://stackoverflow.com/questions/6885148/haskell-error-naked-expression-at-top-level