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

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


Richard,

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.

Serge.

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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