Debugging 查看cabal repl/ghci中通用容器的数据内容
假设我有以下几点：Debugging 查看cabal repl/ghci中通用容器的数据内容,debugging,haskell,ghci,Debugging,Haskell,Ghci,假设我有以下几点： --Main.hs module Main where import Data.Vector as V import Test main = do let v = V.fromList ([1,2]::[Int]) print (getLength v) 以及： --Test.hs module Test where import Data.Vector as V getLength :: (Show a) => V.Vector a -> Int
--Main.hs
module Main where
import Data.Vector as V
import Test
main = do
let v = V.fromList ([1,2]::[Int])
print (getLength v)
--Test.hs
module Test where
import Data.Vector as V
getLength :: (Show a) => V.Vector a -> Int
getLength vec = let l = V.length vec in -- line 6
l
getLengthvec> cabal repl
> :break Test 6
> main
Stopped at Test.hs:6:25-36
_result :: Int = _
vec :: Vector a = _
> vec
<interactive>:4:1:
No instance for (Show a) arising from a use of ‘print’
Cannot resolve unknown runtime type ‘a’
Use :print or :force to determine these types
Relevant bindings include
it :: Vector a (bound at <interactive>:4:1)
Note: there are several potential instances:
instance Show Double -- Defined in ‘GHC.Float’
instance Show Float -- Defined in ‘GHC.Float’
instance (Integral a, Show a) => Show (GHC.Real.Ratio a)
-- Defined in ‘GHC.Real’
...plus 45 others
In a stmt of an interactive GHCi command: print it
>阴谋集团repl
>：断裂试验6
>主要
在测试时停止。hs:6:25-36
_结果：：Int=_
向量a=_
>vec
:4:1:
没有因使用“打印”而导致（显示a）的实例
无法解析未知的运行时类型“a”
使用：打印或：强制确定这些类型
相关绑定包括
它：：向量a（在：4:1处绑定）
注意：有几个潜在的例子：
实例Show Double——在“GHC.Float”中定义
实例Show Float——在“GHC.Float”中定义
实例（积分a，显示a）=>Show（GHC.Real.Ratio a）
--在“GHC.Real”中定义
…再加上45个人
在交互式GHCi命令的stmt中：打印它
我尝试过使用
：force：printgetLengthMain.hsgetLengthvectoListλ :print vec
vec = (_t1::Vector a)
λ :force vec
vec = Data.Vector.Vector 0 2 _
λ :print vec
vec = Data.Vector.Vector 0 2 (_t2::GHC.Prim.Array# a)
λ let as = toList vec
λ :print as
as = (_t6::[a])
λ :force as
as = [1,2]
λ :print vec
vec = Data.Vector.Vector 0 2 (_t7::GHC.Prim.Array# Int)
λ :force vec
vec = Data.Vector.Vector 0 2 _
λ print vec
fromList [1,2]
谢谢你知道为什么当
getLengthgetLengthMain.hs