Simon Marlow 书中严格评价的例子 "Parallel and Concurrent Programming in Haskell"
The example of strict evaluation from Simon Marlow's book "Parallel and Concurrent Programming in Haskell"
Simon Marlow 在他的书“Haskell 中的并行和并发编程”中写道：
The insert operation hadthis line:
putMVar m (Map.insert name number book)
This places in the MVar the unevaluated expression Map.insert name number book.
If we were to do many insert operations consecutively, the MVar would build up a large chain of unevaluated expressions.
To get brief locking and no space leaks, we need to use
a trick:
let book' = Map.insert name number book
putMVar m book'
seq book' (return ())
With this sequence, we’re storing an unevaluated expression in the MVar, but it is evaluated immediately after the putMVar.
我不明白。 seq a b 运算以弱头范式计算 a。所以会有unevaluated expression。如我所见，只会评估 Map 构造函数，而不会评估其所有内容。
As I can see only the Map constructor will be evaluated and all of it contents will be unevaluated.
在内部，Map 类型是使用严格的树实现的。要么评估整个树脊，要么评估它的 none。这是库代码的片段：
data Map k a = Bin {-# UNPACK #-} !Size !k a !(Map k a) !(Map k a)
| Tip
严格性注释 (!) 防止将未计算的值存储为子树。因此，如果我们将 Map k a 值评估为弱头部范式，我们实际上会完全评估树脊。
Map.insert 中的 Map 不是地图构造函数。它是一个模块名称。函数 insert :: Ord k => k -> a -> Map k a -> Map k a is called here. Its result will get evaluated to WHNF before return () is calculated as the next computational step in the combined IO action, thanks to the call to seq. You can consult the source of insert 了解详情。它会通过爆炸模式等进行大量强制操作。
Simon Marlow 在他的书“Haskell 中的并行和并发编程”中写道：
The insert operation hadthis line:
putMVar m (Map.insert name number book)This places in the MVar the unevaluated expression
Map.insert name number book. If we were to do many insert operations consecutively, the MVar would build up a large chain of unevaluated expressions. To get brief locking and no space leaks, we need to use a trick:let book' = Map.insert name number book putMVar m book' seq book' (return ())With this sequence, we’re storing an unevaluated expression in the MVar, but it is evaluated immediately after the putMVar.
我不明白。 seq a b 运算以弱头范式计算 a。所以会有unevaluated expression。如我所见，只会评估 Map 构造函数，而不会评估其所有内容。
As I can see only the
Mapconstructor will be evaluated and all of it contents will be unevaluated.
在内部，Map 类型是使用严格的树实现的。要么评估整个树脊，要么评估它的 none。这是库代码的片段：
data Map k a = Bin {-# UNPACK #-} !Size !k a !(Map k a) !(Map k a)
| Tip
严格性注释 (!) 防止将未计算的值存储为子树。因此，如果我们将 Map k a 值评估为弱头部范式，我们实际上会完全评估树脊。
Map.insert 中的 Map 不是地图构造函数。它是一个模块名称。函数 insert :: Ord k => k -> a -> Map k a -> Map k a is called here. Its result will get evaluated to WHNF before return () is calculated as the next computational step in the combined IO action, thanks to the call to seq. You can consult the source of insert 了解详情。它会通过爆炸模式等进行大量强制操作。