From ff432e262e65243cbc983fcb002527f8fae8c78b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Fri, 9 Apr 2010 15:50:17 +0200
Subject: EEP-23: Allow variables in fun M:F/A

Currently, the external fun syntax "fun M:F/A" only supports
literals. That is, "fun lists:reverse/1" is allowed but not
"fun M:F/A".

In many real-life situations, some or all of M, F, A are
not known until run-time, and one is forced to either use
the undocumented erlang:make_fun/3 BIF or to use a
"tuple fun" (which is deprecated).

EEP-23 suggests that the parser (erl_parse) should immediately
transform "fun M:F/A" to "erlang:make_fun(M, F, A)". We have
not followed that approach in this implementation, because we
want the abstract code to mirror the source code as closely
as possible, and we also consider erlang:make_fun/3 to
be an implementation detail that we might want to remove in
the future.

Instead, we will change the abstract format for "fun M:F/A" (in a way
that is not backwards compatible), and while we are at it, we will
move the translation from "fun M:F/A" to "erlang:make_fun(M, F, A)"
from sys_pre_expand down to the v3_core pass. We will also update
the debugger and xref to use the new format.

We did consider making the abstract format backward compatible if
no variables were used in the fun, but decided against it. Keeping
it backward compatible would mean that there would be different
abstract formats for the no-variable and variable case, and tools
would have to handle both formats, probably forever.

Reference: http://www.erlang.org/eeps/eep-0023.html
---
 erts/doc/src/absform.xml          | 3 ++-
 erts/emulator/test/code_SUITE.erl | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

(limited to 'erts')

diff --git a/erts/doc/src/absform.xml b/erts/doc/src/absform.xml
index 4c84412dd6..88e8b284fb 100644
--- a/erts/doc/src/absform.xml
+++ b/erts/doc/src/absform.xml
@@ -285,7 +285,8 @@
       <item>If E is <c><![CDATA[fun Name / Arity]]></c>, then
        Rep(E) = <c><![CDATA[{'fun',LINE,{function,Name,Arity}}]]></c>.</item>
       <item>If E is <c><![CDATA[fun Module:Name/Arity]]></c>, then
-       Rep(E) = <c><![CDATA[{'fun',LINE,{function,Module,Name,Arity}}]]></c>.</item>
+       Rep(E) = <c><![CDATA[{'fun',LINE,{function,Rep(Module),Rep(Name),Rep(Arity)}}]]></c>.
+      (Before the R15 release: Rep(E) = <c><![CDATA[{'fun',LINE,{function,Module,Name,Arity}}]]></c>.)</item>
       <item>If E is <c><![CDATA[fun Fc_1 ; ... ; Fc_k end]]></c> 
        where each <c><![CDATA[Fc_i]]></c> is a function clause then Rep(E) =
       <c><![CDATA[{'fun',LINE,{clauses,[Rep(Fc_1), ..., Rep(Fc_k)]}}]]></c>.</item>
diff --git a/erts/emulator/test/code_SUITE.erl b/erts/emulator/test/code_SUITE.erl
index 29cbdedd17..db26655c15 100644
--- a/erts/emulator/test/code_SUITE.erl
+++ b/erts/emulator/test/code_SUITE.erl
@@ -278,7 +278,8 @@ t_check_old_code(Config) when is_list(Config) ->
 
 external_fun(Config) when is_list(Config) ->
     ?line false = erlang:function_exported(another_code_test, x, 1),
-    ?line ExtFun = erlang:make_fun(id(another_code_test), x, 1),
+    AnotherCodeTest = id(another_code_test),
+    ExtFun = fun AnotherCodeTest:x/1,
     ?line {'EXIT',{undef,_}} = (catch ExtFun(answer)),
     ?line false = erlang:function_exported(another_code_test, x, 1),
     ?line false = lists:member(another_code_test, erlang:loaded()),
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