From ff432e262e65243cbc983fcb002527f8fae8c78b Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= 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 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'erts/doc') 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 @@ If E is , then Rep(E) = . If E is , then - Rep(E) = . + Rep(E) = . + (Before the R15 release: Rep(E) = .) If E is where each is a function clause then Rep(E) = . -- cgit v1.2.3 From af5edfe20b24116fa892a37a746f4053fde6039b Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Thu, 29 Sep 2011 08:13:24 +0200 Subject: beam_asm: Strenghten the calculation of Uniq for funs Funs are identified by a triple, , where Module is the module name, Uniq is a 27 bit hash value of some intermediate representation of the code for the fun, and index is a small integer. When a fun is loaded, the triple for the fun will be compared to previously loaded funs. If all elements in the triple in the newly loaded fun are the same, the newly loaded fun will replace the previous fun. The idea is that if Uniq are the same, the code for the fun is also the same. The problem is that Uniq is only based on the intermediate representation of the fun itself. If the fun calls local functions in the same module, Uniq may remain the same even if the behavior of the fun has been changed. See http://erlang.org/pipermail/erlang-bugs/2007-June/000368.htlm for an example. As a long-term plan to fix this problem, the NewIndex and NewUniq fields was added to each fun in the R8 release (where NewUniq is the MD5 of the BEAM code for the module). Unfortunately, it turns out that the compiler does not assign unique value to NewIndex (if it isn't tested, it doesn't work), so we cannot use the triple as identification. It would be possible to use , but that seems ugly. Therefore, fix the problem by making Uniq more unique by taking 27 bits from the MD5 for the BEAM code. That only requires a change to the compiler. Also update a test case for cover, which now fails because of the stronger Uniq calculation. (The comment in test case about why the Pid2 process survived is not correct.) --- erts/doc/src/erlang.xml | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'erts/doc') diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml index 45b66a4909..5d7ff7613b 100644 --- a/erts/doc/src/erlang.xml +++ b/erts/doc/src/erlang.xml @@ -1196,11 +1196,16 @@ true {new_uniq, Uniq} -

Uniq (a binary) is a unique value for this fun.

+

Uniq (a binary) is a unique value for this fun. + It is calculated from the compiled code for the entire module.

 {uniq, Uniq} -

Uniq (an integer) is a unique value for this fun.

+

Uniq (an integer) is a unique value for this fun. + Starting in the R15 release, this integer is calculated from + the compiled code for the entire module. Before R15, this + integer was based on only the body of the fun. +

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