bartblast
Consider the following code:
iex> fn1 = fn x -> x end
#Function<42.3316493/1 in :erl_eval.expr/6>
iex> fn2 = fn x -> x end
#Function<42.3316493/1 in :erl_eval.expr/6>
iex> fn1 == fn2
false
iex> m = %{fn1 => 123}
%{#Function<42.3316493/1 in :erl_eval.expr/6> => 123}
iex> m[fn2]
nil
Is there some way to determine whether 2 anonymous functions are equal? By equal we can mean having the same underlying AST or being equivalent in some way.
Another related question:
what is “42.3316493/1” and is it possible to get this number programmatically somehow?
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jhogberg
Two anonymous functions are equal if they were created from the same definition (same
fn ...statement) in the same module (same checksum), and have the exact same environment variables.Funs defined in the shell satisfy the first two as long as their arity is the same, but differ in the latter as they’re interpreted by the shell which drags in a ton of stuff to their environment. If you want consistent results please try this with compiled modules instead.
Also Liked
jhogberg
Yes.
Yes, because you’re consistently comparing different definitions. Different
fn ... endstatements yield different funs. If you were to compare the result offun_1to the result of another invocation offun_1, they would compare equal.LostKobrakai
Function.infocan do that.KristerV
you sound like you know what you’re doing, but i feel like asking what you’re trying to accomplish anyway
Last Post!
hst337
There is no way to have semantic equality for anonymous functions. However, if you want to compare functions you’ve defined in your project, it can be achieved by metaprogramming.
Plus, there is always a space for fetching debug_info from beam files, transpiling AST, performing context checks, checking captured variables, etc. But that’s a lot of job to do