Maybe monad: where is the join and nested Nothing

is the definition of Maybe monad: instance Monad Maybe where return = Just Nothing >>= _ = Nothing ... arrow. The definiton of Maybe functor and fmap: instance Functor Maybe where -- fmap :: (a -> b ... ) -> Maybe a -> Maybe b fmap _ Nothing = Nothing fmap f (Just x) = Just (f x) You can blend the f ... , fmap and join together, the result is the same as bind, the process will be like this Nothing

Haskell map mapM mapM_ example

The Control.Monad module contains a series of functions like mapM, mapM_, how and when to use ... unsafePerformIO $ foo !! 1 Now change the map to mapM. Evaluate it in repl will trigger the IO action one ... by one the type of the mapM version is IO [()]. You can read it as IO of list of actions, the map ... of mapM_ is mapM_ f list = sequence_ (map f list).

Latin roots differences cit, licit, elicit and plicit

the same Latin root, but they are three different roots and the meanings are quite different ... shareholder value. [licit in elicit means to entice, lure, deceive] The licit here comes from licitus ... Let's see some English words: explicit, solicit, elicit, and illicit. They all look like using ... . [plicit means fold, curve, turn, bend] The explicit, ex means outward, fold out, unfold. If you fold

USB Mass Storage Device get error code 38: previous instance still in memory

on the tip of the "USB Mass Storage Device". Open property page, the message tells a previous instance ... ", which used to be "USB Mass Storage Device". I looked at their signature, the date of "USB Mass ... still in memory. To make it work again, just reboot, or disable the device driver and reenable ... Storage Device" is 2006, and the "Realtek USB 3.0 Card Reader" is 2013, I'm not sure if it's the date

How to create a dummy windows exe runs in the background

solution will be to replace the executable file with a dummy windows program of the same name ... One way to prevent a program from being launched is to delete the executable file and create ... that will run in the background without anything noticeable in the front. Here is a solution, build ... . If there are second or third occasion where a dummy window executable is needed, we need to use

Combine multiple PDF files into single PDF file in Clojure

want. Here is how to combine pdf files into one file (defn read-pdf-bytes [file-path ... , it's better to pack them together into a single PDF file. I'd used the clj-pdf to pack a set ... of merge-pdf function (defn merge-pdfs "merge multiple PDFs into output file" [& {:keys ... . Such as saving a slide which consists of a series of orderd images, or a newspaper provided as PDF files

How to invoke Java method in Clojure

[Call overloaded Java methods] I get this problem, I want to call the get method ... is represented as array, in Java if there is no variable length parameter we just omit it, but in Clojure, we ... need to specify it explicitly to make it match the type signature of Java method, we need to pass ... of java.nio.file.Paths from clojure, I tried a lot of options, but I always get this error cannot be cast

Replace date string in text file in Windows

I get a text file that contains a date string, what I want to do is execute a string ... will perform the search and replace in file, other wise sed will just output the replaced string to console ... /..\/node_2/%day%\/node_2/" D:\www\node\index.htm It replace a string like the following 03/node_2 ... . Create a new task schedule on Windows and set up the execution time and set the bat file

Utterly Completely Totally What's the differences

utterly. the situation is completely normal interact with people in a way that feels utterly normal ... will perceive it. >the situation is completely normal It's normal , don't panic, there is no big ... deal. The author worries the readers won't be convinced and doubt about it. By the completely normal ... it. >the situation is utterly normal Utterly means "truly, plainly, outspokenly". The verb utter

Emacs defvar doesn't take effect

One of the common problem an Emacs newbie would commit is take defvar literally ... . The defvar can associate a non-nil value with an variable only once. ELISP> (defvar aa 3) aa ELISP> aa ... 3 (#o3, #x3, ?\C-c) ELISP> (defvar aa 4) aa ELISP> aa 3 (#o3, #x3, ?\C-c) ELISP> (setq aa 4 ... ) 4 (#o4, #x4, ?\C-d) ELISP> aa 4 (#o4, #x4, ?\C-d) The story always goes this way: you use defvar
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