Two notes: Let bindings do not have order. Using them in the way suggested implies order. In this world, they would have to be ordered or confusion would reign. This is more imperative style.
I've actually really disliked this in CoffeeScript/Ruby, that implicitly the last item in the block is the thing returned. Makes it a lot harder to parse mentally. -1. On Fri, Apr 14, 2017 at 10:00 PM, Akio Burns <burns...@gmail.com> wrote: > It's not clear to me why Elm uses `let`, instead of simply scoping > definitions to the expression below them. > > > With `let`: > > foo = > let > a = 1 > b = 2 > in > a + b > > Scoping definitions to the expression below them: > > foo = > a = 1 > b = 2 > > a + b > > > I understand that each function must contain a single expression. In Elm, > although they contain expressions, definitions are not expressions. > > > Visualized: > > foo = > <EXPRESSION HERE> > > foo = > a + 2 <- EXPRESSION > > foo = > a = 1 <- DEFINITION SCOPED TO THE a + 2 EXPRESSION > a + 2 > > > Another way to demonstrate scope is: > > let > a = 1 > b = 2 > in > a + b > > would become (parenthesis to demonstrate scope): > > ( > a = 1 > b = 2 > > a + b > ) > > > It seems to me that `let` and `in` are unnecessary and verbose. Put another > way, I think few people would agree that requiring a keyword before variable > assignment `set a = 1` would be a good idea. The `=` makes the intent > explicit. Likewise, indentation—or parenthesis—could make scopes explicit, > and `let` and `in` unnecessary. > > Some have argued that without `let`, we could not have arbitrarily nested > scopes. I don't have significant experience with Elm, but I would guess that > nesting `let`s today is pretty big code smell. Instead of nesting `let`s to > reuse variable names, developers should either pick more descriptive > variable names, or abstract into a function. > > > This could—of course—apply anywhere an expression is expected: > > True -> > x = 0 > y = 0 > > (x, y) > ... > > > @rtfeldman on the Slack pointed out that this syntax is more diff friendly: > > if I write a view function like > view model = > div [] > [ ... lots of other stuff ] > > and then I want to introduce a nested constant like so: > view model = > let > foo = ... > in > div [] > [ ... lots of other stuff ] > > the fact that I indented the final expression makes the VCS diff explode > this happens to me all the time, and it's pretty annoying > with [this] idea it wouldn't happen anymore > > > Lastly, here's elm-todomvc with scoped definitions, courtesy of @rtfeldman > again: > > https://github.com/rtfeldman/elm-todomvc/blob/8678c8bcaeb5cb4b3f87dbefb7a01b5fe492dbc7/Todo.elm > > -- > You received this message because you are subscribed to the Google Groups > "Elm Discuss" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to elm-discuss+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Elm Discuss" group. To unsubscribe from this group and stop receiving emails from it, send an email to elm-discuss+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
