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The ms_transform module, used by ets:fun2ms/1 and dbg:fun2ms,
evaluates constant arithmetic expressions. This is necessary since the
Erlang compiler, which normally evaluates constant expressions, does
not recognize the format generated by ms_transform.
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Running 'dbg:fun2ms(fun([]) -> return_trace() end' resulted in an error
"dbg:fun2ms requires fun with single variable or list parameter"
But the empty list is actually a list and it is a valid value as a
match-spec head (matching on arity-0 functions).
Although its practical use is questionable this commit eliminates a
small limitation of ms_transform which is not present in the match-spec
grammar.
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* maint:
Fix miscompilation when module contains multiple named funs
Fix locations of shadowing warnings in ms_transform
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A shadowed variable in an ms_transform match expression emits a warning
located at the match expression instead of the variable.
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This adds optional names to fun expressions. A named fun expression
is parsed as a tuple `{named_fun,Loc,Name,Clauses}` in erl_parse.
If a fun expression has a name, it must be present and be the same in
every of its clauses. The function name shadows the environment of the
expression shadowing the environment and it is shadowed by the
environment of the clauses' arguments. An unused function name triggers
a warning unless it is prefixed by _, just as every variable.
Variable _ is allowed as a function name.
It is not an error to put a named function in a record field default
value.
When transforming to Core Erlang, the named fun Fun is changed into
the following expression:
letrec 'Fun'/Arity =
fun (Args) ->
let <Fun> = 'Fun'/Arity
in Case
in 'Fun'/Arity
where Args is the list of arguments of 'Fun'/Arity and Case the
Core Erlang expression corresponding to the clauses of Fun.
This transformation allows us to entirely skip any k_var to k_local
transformation in the fun's clauses bodies.
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Compile below module resulting incorrect warning:
$ cat tmp.erl
-module(tmp).
-export([tmp/1]).
-include_lib("stdlib/include/ms_transform.hrl").
tmp(X) when X > 100 ->
Y=X,
Y;
tmp(X) ->
ets:fun2ms(fun(Y) -> {X, Y} end).
$ erlc tmp.erl
./tmp.erl:8: Warning: variable 'Y' shadowed in ms_transform fun head
The scope for a variable is its function clause. Variables bound in one
function clause should not interfere with other function clauses.
This patch removes incorrect passing of variable bindings from one
function clause to another.
Signed-off-by: Haitao Li <[email protected]>
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Also changed compiler to allow for warnings in parse_transforms.
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