Re: Strong Types ?

Satish Chandra Gupta <>
27 Apr 2007 11:31:00 -0400

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From: Satish Chandra Gupta <>
Newsgroups: comp.compilers
Date: 27 Apr 2007 11:31:00 -0400
Organization: Compilers Central
References: 07-04-123
Keywords: types
Posted-Date: 27 Apr 2007 11:31:00 EDT

> I faced a question during my research on desing and implementation of
> programming language. The question arises from area of type binding
> and checking in design of programming languages. question :
> Can we call a programming language which has both static type
> checking and static type binding a strongly type programming
> language; if so why and is there any programming language with these
> characteristics.


You might already be aware of a book by Benjamin C. Pierce titled
"Types and Programming Languages"

I am describing here in very brief, strongly typed languages has a
sound type system characterized by 2 properties: progress and
preservation. The progress is: given an expression e, it is either a
value, or the evaluation of e progresses to another expression e'. The
preservation is: if e is of type T, and evaluation of e progresses to
e', then type of e' is still T.

I understand that these 2 rules sound very abstract, but Benjamin's
book start from a very simple language examples to modeling quite
complex languages with sub-typing, but still keeping these 2 rules at
kernel. I found that amazing. People have also done type system for a
small subset of Java (Featherweight Java) which preserves OO
characteristics such as classes, inheritance, dynamic typecasts and
generics/templates (,
perhaps you want to take a look at that.


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