@trace_mutating

[cstjean]

We can generate another tracing version, that stores the arguments' printed representation if is_mutable(obj) returns true. We can have that is_mutable(x) = isbits(x) by default.

[cstjean]

Even better: keep @trace, but check is_mutable(x) for each.

Alternatively, store each argument as store_val(x), which defaults to x. We can do the same with the return value, although that might slow things down :|