The $ function is essentialy a "no-op". That is, it literally does nothing.
There is no difference in Haskell between a function and a reference to it.
The only purpose of $ is for grouping. The line in question below could have
been written identically as "fromQty <- atomically (readTVar fromBal)". The
$ groups together everything to the end of the line, and can be used to
avoid parentheses that could add noise to the code.
On Mon, Feb 23, 2009 at 1:18 PM, Michael Easter
re: desugaring. Thanks Andrew, that worked great!
I have another, easier question from the same code in RWH:
bogusTransfer qty fromBal toBal = do fromQty <- atomically $ readTVar fromBal [snip]
Can someone please explain the ($) function in English? From the type signature, it seems to be an "apply function", but I can't quite explain when we use it. Clearly, it is used throughout RWH but I haven't found a good explanation.
My guess is that it is when we want an "execution" of a function rather than a mere reference to it. Is that accurate?
thanks again Michael
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