Understanding how guard clauses are parsed, using that AST

[Brian Cardarella]

If I quote the following:

Code.string_to_quoted """

  if foo do

    "true"

  else

    "false"

  end

"""

I get the following AST:

{:if, [line: 1], [{:foo, [line: 1], nil}, [do: "true", else: "false"]]}

Which makes sense to me as the last node is a list. However, `when` seems to follow different rules and I'm not following exactly how Elixir parses it from the AST:

Code.strig_to_quoted """

  def foo(bar) when bar == 1 do

    "baz"

  end

"""

{:def, [line: 1],

 [{:when, [line: 1],

   [{:foo, [line: 1], [{:bar, [line: 1], nil}]},

    {:==, [line: 1], [{:bar, [line: 1], nil}, 1]}]}, [do: "baz"]]}

`when` is not in that last list, but is now the first element in the values for `:def`

Can someone point me to examples of how Elixir is parsing `when` within the source? I dug around in Kernel which brought me to elixir_def but got stuck there.

Use case: I am experimenting with writing some macro functions that could take guard clauses.

[Michał Muskała]

when is an operator - it behaves very similar to operators like == or in.

iex(1)> quote(do: 1 when 2)

{:when, [], [1, 2]}

iex(2)> quote(do: 1 == 2)

{:==, [context: Elixir, import: Kernel], [1, 2]}

In case of def, the left side (of the operator) is the call and right the guards.

Michał.

[Brian Cardarella]

Ah, that explains everything! Thank you :)