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Intro to Elixir macro
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tony612
May 22, 2017
Programming
2
150
Intro to Elixir macro
keynote at Elixir Meetup 2017.5.21
https://www.meetup.com/Elixir-Shanghai/events/238614338/
tony612
May 22, 2017
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Transcript
*OUSPUP&MJYJSNBDSP !UPOZ
0WFSWJFX ˙ 8IBU’TNBDSP ˙ 8IZNBDSP ˙ )PXJTNBDSPJNQMFNFOUFEJO&MJYJS ˙
)PXUPVTF ˙ 8IFOUPVTF
8IBU’TNBDSP
"NBDSPJTBOPSEJOBSZQJFDFPG-JTQDPEFUIBU PQFSBUFTPOBOPUIFSQJFDFPGQVUBUJWF-JTQ DPEF USBOTMBUJOHJUJOUP BWFSTJPODMPTFSUP FYFDVUBCMF-JTQ .BDSPJO-JTQ IUUQDMDPPLCPPLTPVSDFGPSHFOFUNBDSPTIUNM
"NBDSPJTBOPSEJOBSZQJFDFPG&MJYJSDPEF UIBUPQFSBUFTPOBOPUIFSQJFDFPGRVPUFE&MJYJS DPEF USBOTMBUJOHJUJOUPRVPUFE&MJYJS .BDSPJO&MJYJS
EFGNBDSP defmodule MyLogic do defmacro unless(expr, opts) do quote do
if !unquote(expr), unquote(opts) end end end require MyLogic MyLogic.unless false do IO.puts "It works" end
&MJYJSDPEFUP"45 sum(1, 2, 3) => {:sum, [], [1, 2, 3]}
x => {:x, [], Elixir} %{1 => 2} => {:%{}, [], [{1, 2}]} Foo.run(1, 2) => {{:., [], [{:__aliases__, [alias: false], [:Foo]}, :run]}, [], [1, 2]}
RVPUF quote do defmodule Foo do def foo do 1
end end end {:defmodule, [context: Elixir, import: Kernel], [{:__aliases__, [alias: false], [:Foo]}, [do: {:def, [context: Elixir, import: Kernel], [{:foo, [context: Elixir], Elixir}, [do: 1]]}]]}
.FUBQSPHSBNNJOH XJLJQFEJB ˙ $PNQVUFSQSPHSBNTIBWFUIFBCJMJUZUPUSFBU QSPHSBNTBTUIFJSEBUB ˙ "QSPHSBNDBOCFEFTJHOFEUPSFBE HFOFSBUF BOBMZTFPSUSBOTGPSNPUIFSQSPHSBNT
8IZNBDSP
.FUBQSPHSBNNJOH XJLJQFEJB ˙ .JOJNJ[FUIFBNPVOUPGDPEFUPFYQSFTTB TPMVUJPO BOEUIVTSFEVDJOHUIFEFWFMPQNFOU UJNF ˙ .PWFDPNQVUBUJPOTGSPNSVOUJNFUPDPNQJMF UJNF
˙ (FOFSBUFDPEFVTJOHDPNQJMFUJNF DPNQVUBUJPOT
MFTTDPEF NPSFFFDUJWF defmodule MyRouter do use Plug.Router plug :match #
middleware plug :dispatch # middleware get "/hello" do # logic for a route send_resp(conn, 200, "world") end end
DPNQVUFBUDPNQJMFUJNF # config.yml web_port: 8080 Config.get(:web_port) => 8080 OPUBHPPEFYBNQMF
(FOFSBUFDPEF iex> String.upcase("Elixir Shànghăi") "ELIXIR SHÀNGHĂI" IUUQTHJUIVCDPNFMJYJSMBOHFMJYJSCMPCNBTUFS MJCFMJYJSVOJDPEFVOJDPEFFY-
)PXJTNBDSPJNQMFNFOUFE JO&MJYJS
$PNQJMJOHPG&MJYJS
"OFYBNQMF defmodule Foo do defmacro add1(x) do quote do x
+ 1 end end end Foo.add1(2)
$PEFUP"45 quote do: Foo.add1(2) => { {:., [], [{:__aliases__, [alias:
false], [:Foo]}, :add1]}, [], [2]}
.BDSPFYQBOTJPO require Foo Macro.expand(quote(do: Foo.add1(2)), __ENV__) => {:+, [context: Foo,
import: Kernel], [{:x, [], Foo}, 1]} quote do: Foo.add1(2) => { {:., [], [{:__aliases__, [alias: false], [:Foo]}, :add1]}, [], [2]}
Macro.to_string({:+, [context: Foo, import: Kernel], [{:x, [], Foo}, 1]}) =>
"x + 1" "45UPDPEF
4PPVSDPEFDIBOHFTBGUFSFYQBOTJPO Foo.add1(2) => x + 1
None
)PXUPVTF
5IJOLPGUIFOBMDPEF BGUFSFYQBOTJPO %FOFNBDSPTUPHFOFSBUFUIFDPEF 8SJUFBOESVOVOJUUFTUT PSSVOJOJFY 3FQFBU
&YBNQMFBTJNQMF'4.MJC VTJOH%4-
6TBHFPGUIFMJC defmodule Door do trans :push, "closed", "opened" trans :pull,
"opened", "closed" end state0 = "closed" state1 = Door.push(state0) # "opened" state2 = Door.pull(state1) # "closed"
5IFFYQBOEFEDPEF defmodule Door do def push("closed") do "opened" end def
pull("opened") do "closed" end end
4PXFOFFE 5IFBCJMJUZUPJOKFDUNBDSPUSBOT 6TFUSBOTUPHFOFSBUFGVODUJPOT
IUUQTIFYEPDTQNFMJYJS,FSOFMIUNMVTF VTFUPJOKFDUBNPEVMF
defmodule Door do use FSM trans :push, "closed", "opened" trans
:pull, "opened", "closed" end # expanded => defmodule Door do import FSM.DSL, only: [trans: 3] # ... end
defmodule FSM do defmacro __using__(opts) do quote do import FSM.DSL,
only: [trans: 3] end end end defmodule FSM.DSL do defmacro trans(name, from, to) do # ... end end
*NQMFNFOUUSBOTJO'4.%4- defmacro trans(name, from, to) do quote do def name(from)
do to end end end 5IJTJTXSPOH
(FOFSBUFEDPEFXJMMCF defmodule Door do def name(from) do to end def
name(from) do to end end 5IJTJTXSPOH
VORVPUFUPDPNQVUFFYQSFTTJPO CFGPSFNBDSPFYQBOTJPO defmacro trans(name, from, to) do quote do def
unquote(name)(unquote(from)) do unquote(to) end end end
5IFDPEFDBOCFSVOJOJFY IUUQTHJTUHJUIVCDPN UPOZDDGFCCDBCFB MFGTNFYT
"OBEWBODFEGFBUVSF -JTUBMMFWFOUTPGUIF'4.
defmodule Door do use FSM trans :push, "closed", "opened" trans
:pull, "opened", "closed" end Door.__events__ # => [:push, :pull]
˙ 8FDBOVTFNPEVMFBUUSJCVUFTUPTBWFBMMFWFOUT ˙ #VUNPEVMFBUUSJCVUFTDBO’UCFBDDFTTFEJO SVOUJNF ˙ 4PXFOFFEBGVODUJPOUPTBWFUIFBUUSJCVUFTJOB NPEVMFKVTUCFGPSFDPNQJMJOH DPNQJMFEUP CZUFTDPEF
IUUQTIFYEPDTQNFMJYJS.PEVMFIUNMNPEVMFDPNQJMFDBMMCBDLT
defmodule Door do @before_compile FSM.DSL # ... # expanded def
__events__ do # ... end end
defmodule FSM do defmacro __using__(opts) do quote do @before_compile FSM.DSL
end end end defmodule FSM.DSL do defmacro __before_compile__(env) do quote do def __events__ do # ... end end end end
6TFNPEVMFBUUSJCVUFTUPMJTUFWFOUT defmodule FSM do defmacro __using__(opts) do quote do Module.register_attribute(__MODULE__,
:events, accumulate: true) end end end defmacro trans(name, from, to) do quote do @events unquote(name) # ... end end
BOEEFOF@@FWFOUT@@ CFGPSFDPNQJMJOH defmodule FSM.DSL do defmacro __before_compile__(env) do fields =
Module.get_attribute(env.module, :events) quote do def __events__ do unquote(Enum.reverse(fields)) end end end end
5IFDPEFDBOCFSVOJOJFY IUUQTHJTUHJUIVCDPN UPOZDDGFCCDBCFBMFGTN FYT
8IFOUPVTFNBDSP
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IUUQFMJYJSMBOHPSHHFUUJOHTUBSUFENFUBNBDSPTIUNMXSJUFNBDSPTSFTQPOTJCMZ 8SJUFNBDSPTSFTQPOTJCMZBOELFFQZPVS NBDSPEFOJUJPOTTIPSU
IUUQFMJYJSMBOHPSHHFUUJOHTUBSUFENFUBNBDSPTIUNM &YQMJDJUJTCFUUFSUIBOJNQMJDJU$MFBSDPEF JTCFUUFSUIBODPODJTFDPEF
2"