EP002 - A new, better, more usable Prelude

proposals/EP002-NewPrelude.org

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+#+TITLE: EP002 - A new, better, more usable Prelude
+#+DATE:12/03/18
+
+* Motivation
+  The Prelude is the biggest selling point of any programming language, it is the main interface
+  for the users. It is important to give good impression on the first contact with the newcomers
+  so we can acquire them as regular users.
+
+  Also, but not less important. Given that the Prelude is the main building block of any application,
+  it should be extremely readable, given that in the current world of software development it is
+  important that new members of any software project can start working in a project written in
+  Eta without too much hassle.
+
+  We should aim to avoid questions like "What does the L in foldl mean? foldList? foldLeft?" or
+  "What is the difference between map and fmap? Why should I avoid String?" .
+
+  We should not forget to include all the necessary abstractions from modules like ~Data.Functor~,
+  ~Data.Monoid~ and so on.
+
+* Teachability
+  The main way of teaching the Prelude would be in the official documentation and tutorials.
+
+* Summary
+  We expect to add a module called ~Eta~ that should be imported in all source files within the
+  Eta language. We can do even better if we automatically import this module for all files with the
+  ~*.eta~ extension.
+
+* Design
+** Aliases
+*** Operators
+    - Pipe backwards ~<|~. Alias for ~$~.
+    - Pipe forward ~|>~. Alias for ~flip ($)~.
+    - Map backwards ~<$|~. Alias for ~<$>~.
+    - Map forward ~|$>~. Alias for ~flip (<$>)~.
+    - Apply backwards ~<*|~. Alias for ~<*>~.
+    - Apply forward ~|*>~. Alias for ~flip (<*>)~.
+    - Flatmap backwards ~<<|~. Alias for ~=<<~.
+    - Flatmap forward ~|>>~. Alias for ~>>=~.
+    - ~<+>~. Alias for ~<>~ in the ~Monoid~ class.
+     This might clash with ~<+>~ from ~Arrow~, but it might make sense to swap them,
+     as the mathematical symbol for monoids is much more similar to ~<+>~, and
+     for newcomers it implies concatenation automatically.
+
+    The main reason for these aliases is to allow writing code in a more natural way for newcomers.
+    For example:
+
+    #+BEGIN_SRC haskell
+    myFunction :: [Int] -> IO ()
+    myFunction someInputData
+        = someInputData
+        |>  filter (>2)
+        |>  map (+ 4)
+        |>  monadicMap (\id -> readFile $ show id <> "_data.txt")
+        |$> length
+        |>> print
+    #+END_SRC
+
+*** Functions
+    - ~identity~. Alias for ~id~.
+     We might be interested in removing support for ~id~ as it is a common
+     name in all domain models.
+    - ~first~. Alias for ~fst~ for tuples
+    - ~second~. Alias for ~snd~ for tuples
+    - ~constantly~. Alias for ~const~.
+    - ~successor~. Alias for ~succ~ in the ~Enum~ class.
+    - ~predecessor~. Alias for ~pred~ in the ~Enum~ class.
+    - ~map~ becomes an alias for ~fmap~. Dropping the list function
+    - ~mapFirst~. Alias for ~first~ in the ~Bifunctor~ class. 
+    - ~mapSecond~. Alias for ~second~ in the ~Bifunctor~ class. 
+     They should be redefined so they don't clash with the tuple functions.
+    - ~apply~. Alias for ~<*>~ from the ~Applicative~ class.
+    - ~flatMap~. Alias for ~=<<~ from the ~Monad~ class.
+    - Although ~return~ shouldn't be touched. We should advise to use ~pure~.
+     This would help newcomers to not get confused with the "regular" return
+     keyword in other languages.
+    - ~monoidIdentity~. Alias for ~mempty~ in the ~Monoid~ class.
+    - ~monoidAppend~. Alias for ~mappend~ in the ~Monoid~ class.
+    - ~monoidConcat~. Alias for ~mconcat~ in the ~Monoid~ class.
+    - ~isElementOf~. Alias for ~elem~.
+    - ~notElementOf~. Alias for ~notElem~.
+    - ~foldLeft~. Alias for ~foldl~.
+    - ~foldRight~. Alias for ~foldr~.
+    - ~strictFoldLeft~. Alias for ~foldl'~.
+    - ~strictFoldRight~. Alias for ~foldr'~.
+     The fold aliases imply the ones from the ~Foldable~ class.
+    - ~discard~. Alias for ~void~
+    - ~monadicMap~. Alias for ~mapM~
+    - ~discardMonadicMap~. Alias for ~mapM_~
+    - Probably many more there to improve readability.
+** Additions
+   We should provide total alternatives to functions like ~head~, ~read~, etc...
+   These would be replaced with ~unsafeHead~, ~unsafeRead~, etc... denoting that they
+   are not recommended to use.
+
+** A better numerical hierarchy
+   Add support for NumHask (https://github.com/tonyday567/numhask), so that users can benefit from a nicer
+   numerical hierarchy, specially for data science.
+
+   This prelude is 100% compatible with the current Haskell Prelude, and it makes no breaking changes, as it
+   just adds a nicer class hierarchy and QuickCheck properties.
+
+* Unresolved
+  If we wanted to use "regular" Haskell functions, we might have some troubles with the new
+  aliases/additions. This could be fixed by importing some ~Eta.Legacy~ module.
+