Haskell中的字符串插值

Question

我想编写将输出的代码:

length [1,2,3] => 3   

在 Ruby 中，我可以这样做:

puts "length [1,2,3] => #{[1,2,3].length}"

以下尝试是 Haskell 失败...

Prelude Data.List> print "length [1,2,3]"
"length [1,2,3]"
Prelude Data.List> print (length [1,2,3])
3
Prelude Data.List> print "length [1,2,3]" (length [1,2,3])

<interactive>:1:0:
  Couldn't match expected type `Int -> t'
     against inferred type `IO ()'
 In the expression: print "length [1,2,3]" (length [1, 2, 3])
 In the definition of `it':
      it = print "length [1,2,3]" (length [1, 2, 3])
 Prelude Data.List>

Answer 1

您也可以使用 Text.Printf 它包含在 GHC 基础库中:

> let format s = printf "length %s => %d\n" (show s) (length s)
> format [1,2,3]
length [1,2,3] => 3

Hackage 上有几个字符串插值包 http://hackage.haskell.org如果你想要更好的情况。