[erlang-questions] Type specs expressivity

Olivier BOUDEVILLE olivier.boudeville@REDACTED
Fri Sep 9 14:00:55 CEST 2011


I would have three small questions regarding what can be expressed with 
type specs:

        - we can define immediate constants and even ranges for integer 
values (ex: '-spec f() -> 42.' or  '-spec f() -> 0..42.'), but apparently 
we cannot do the same for floats? Is there any particular reason for that 
(besides the lack of meaning of exact comparisons for floating-point 
numbers), or maybe it is a planned enhancement?

        - it is a still more minor point, but we are using a hashtable 
type in pure Erlang, which is implemented as a tuple containing buckets. 
The number of elements of the tuple is determined at run-time (depending 
on a targeted ideal load factor, based on the expected number of elements 
to be stored in the hashtable). We can define a type for bucket(), but for 
the hashtable is there any way of expressing a more precise declaration 
than  '-opaque hashtable() :: tuple()', i.e. to tell that even if we do 
not know the size of the tuple, we know it will contain bucket() instances 
at each position?

        - what is the recommended way of handling functions that may or 
may not throw exceptions? If otherwise returning a type T, should we use T 
| none() or T | no_return() as return type, or should we consider that 
type specs focus on actual return types under normal circumstances, and 
that exceptions are in "another dimension"? I suppose it is the latter 
option, but then one could imagine that type specs for functions could be 
enriched with exception specifications, for example to check whether a 
catch clause has any chance of being triggered at all?

Thanks in advance for any hint,
Best regards,

Olivier Boudeville

EDF R&D : 1, avenue du Général de Gaulle, 92140 Clamart, France
Département SINETICS, groupe ASICS (I2A), bureau B-226
Office : +33 1 47 65 59 58 / Mobile : +33 6 16 83 37 22 / Fax : +33 1 47 
65 27 13

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