“表达式上下文中的模式语法”错误

Question

不知道问题出在哪。继完全HMATRIX buildMatrix DOC：

Prelude Data.Packed.Matrix> let k= buildMatrix 3 4 ((r,c) -> fromIntegral r * fromIntegral c) 

<interactive>:1:26: 
    Pattern syntax in expression context: 
     (r, c) -> fromIntegral r * fromIntegral c 

Answer 1

在文档中，标记不正确转义，它必须是

let k = buildMatrix 3 4 (\(r,c) -> fromIntegral r * fromIntegral c) 

的黑线鳕标记被

{- | creates a Matrix of the specified size using the supplied function to 
to map the row\/column position to the value at that row\/column position. 

@> buildMatrix 3 4 (\ (r,c) -> fromIntegral r * fromIntegral c) 
(3><4) 
[ 0.0, 0.0, 0.0, 0.0, 0.0 
, 0.0, 1.0, 2.0, 3.0, 4.0 
, 0.0, 2.0, 4.0, 6.0, 8.0]@ 

Hilbert matrix of order N: 

@hilb n = buildMatrix n n (\(i,j)->1/(fromIntegral i + fromIntegral j +1))@ 

-} 

反斜线需要为了逃避他们的显示。