[erlang-questions] Why is Erlang what it is?

Serge Aleynikov <>
Fri Dec 22 19:56:57 CET 2006


Thanks for clarification!  I've seen "strict typing" term being used 
before and found that people either meant "strong typing" or "static 
typing" by it.


Richard Carlsson wrote:
> Serge wrote:
>> Could you please define "strict typing" more verbosely.  According to
>> wikipedia (http://en.wikipedia.org/wiki/Type_system) there are primarily
>> three typing groups:
>> 1. Static and dynamic typing
>> 2. Strong and weak typing
>> 3. Safely and unsafely typing
>> What is "strict typing" then?  Dynamic + strong + safe?  Are there any
>> references that discuss this type definition?
> I should apparently be even more careful with the words I use.
> The intended meaning, as related to the classification above, was
> "strongly typed". (Googling for "strictly typed" shows that many
> people seem to have used these words in that sense, but I should
> have known better. ...slaps fingers of self...)
> So what does it mean? Static/dynamic is a separate issue, and I
> had actually never before seen "safely/unsafely" used as a separate
> classification before (except for more specialized type systems, e.g.
> for checking safety of byte code) - it is usually (in my experience at
> least) assumed that "strong/weak" has much more to do with type _safety_
> than with whether implicit casts are allowed, so I don't really agree
> with the Wikipedia entry - but then, I'm not an expert.
> If you've been reading in Wikipedia, you might also have seen the
> separate entry on "Strongly-typed programming language". Let me
> quote it here:
> ``the term strong typing is used to describe how programming languages
> handle datatypes. The antonym is weak typing. However, these terms have
> been given such a wide variety of meanings over the short history of
> computing that it is often difficult to know what an individual writer
> means by using them.
> Programming language expert Benjamin C. Pierce, author of Types and
> Programming Languages and Advanced Types and Programming Languages, has
> said:
>     `I spent a few weeks... trying to sort out the terminology of
>     "strongly typed," "statically typed," "safe," etc., and found it
>     amazingly difficult.... The usage of these terms is so various as
>     to render them almost useless.'
> Most generally, "strong typing" implies that the programming language or
> implementation enforces some kind of constraints upon programs,
> preventing them from running code which uses data in an invalid way.
> [...] However, the nature and strength of these constraints is highly
> variable.''
> (http://en.wikipedia.org/wiki/Strongly-typed_programming_language)
> My personal view of what "strongly typed" (or more sloppily, "strictly
> typed") means is basically that:
>   - every concrete value will have a known specific type
>   - you cannot re-interpret the bit pattern of a value (or access
>     memory that does not contain a proper value), i.e., the only
>     allowed casts, implicit or explicit, are those that convert
>     the representation as necessary - no casting of pointers
> In that sense, Erlang is strongly (an dynamically) typed, while
> something like BCPL would be an example of a weakly typed language.
>     /Richard

Serge Aleynikov
Routing R&D, IDT Telecom
Tel: +1 (973) 438-3436
Fax: +1 (973) 438-1464

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