The previous representation was very hard to compose
and very often required the AST nodes to be created
manually.
The current approach is easier to compose because
the node is represented as any other operator as long
as it is wrapped in parentheses.
For example, imagine we have pairs of patterns and
the code to be executed for that pattern, and we want
to inject them into a case. It can now be writen as:
pairs = Enum.map pairs, fn { pattern, expr } ->
quote do: (unquote(pattern) -> unquote(expr))
end
quote do
case unquote(condition), do: unquote(pairs)
end
Compare to the previous implementation:
pairs = Enum.map pairs, fn { pattern, expr } ->
{ [pattern], [], expr }
end
pairs = { :->, [], pairs }
quote do
case unquote(condition), do: unquote(pairs)
end
This commit includes three changes:
1. Previously, the parallel compiler released at once all processes
depending on a particular module. This commit ensures they are
released according to the number of cores available. This ensures
we have fewer modules being compiled at once
2. Garbage collect the current process every time we are waiting
for another module to be compiled
3. Do not compile a module for files that simply define modules
This commit also simplifies macro expansion for both imports and aliases
to always give higher preference to the macro environment rather than
the caller one, if such is available. The deal is to simplify both the
code and understanding of how macros work.
Prior to this commit, the following code would work:
defmodule Hello do
defmacro write do
quote do
a = 1
end
end
defmacro read do
quote do
a
end
end
end
require Hello
Hello.write
Hello.read
Although this is convenient, it has many issues:
1. It is not clear at any point the intent of sharing the variables
in between the macros
2. Whenever macros from the same module are nested, there is a chance
a variable used before and after the nesting to be overriden
We address this issue by only allowing variables explicitly marked
with var! to be shared. Here is how the example above should be updated:
defmodule Hello do
defmacro write do
quote do
var!(a, Hello) = 1
end
end
defmacro read do
quote do
var!(a, Hello)
end
end
end
require Hello
Hello.write
Hello.read
José Valim
John Warwick
Eric Meadows-Jonsson
Guillaume Grenet
josephwilk
Samuel Tonini