[TYPES] Types of expressions in dynamic languages: "un-typed" or "uni-typed"?

Gavin Mendel-Gleason gavin.mendel.gleason at gmail.com
Wed Jan 8 08:58:50 EST 2014

Sure what's wrong with uni-typing as a description?  If you want to mimic
dynamic typing in a typed programming language, it's trivial to do with a
single type embedding all the types available with a wrapping constructor.
 Unboxing is simply a compiler optimisation removing the constructor
through some sort of partial computation.  Type errors are really just
exceptions that give assertions on the typing constructors allowed in a
given code path.

On 8 January 2014 10:09, Sean McDirmid <smcdirm at microsoft.com> wrote:

> [ The Types Forum, http://lists.seas.upenn.edu/mailman/listinfo/types-list]
> It is difficult to sort any type system into a simple easily named bucket.
> I see Python (and Ruby, Javascript) as dynamically and structurally typed.
> Static structural typing and dynamic nominal typing are completely sensical
> for other languages (especially the former, the latter is possible even if
> it lacks examples).
> I reserve "untyped" for languages where you don't even get a decent
> message-not-understood run-time error (e.g. a memory corruption in C on
> doing something bad to a void*). Untyped is much weaker than a safe dynamic
> language that crashes more elegantly (and more easily debugged) when a type
> error occurs.
> I agree that the concept of uni-typing isn't very useful; it doesn't tell
> us very much about the real typing properties of the language.
> -----Original Message-----
> From: Types-list [mailto:types-list-bounces at lists.seas.upenn.edu] On
> Behalf Of Siraaj Khandkar
> Sent: Wednesday, January 8, 2014 11:12 AM
> To: types-list at lists.seas.upenn.edu
> Subject: [TYPES] Types of expressions in dynamic languages: "un-typed" or
> "uni-typed"?
> [ The Types Forum, http://lists.seas.upenn.edu/mailman/listinfo/types-list]
> We're having a discussion with a friend regarding the most accurate way to
> describe the typing situation in Python.
> His view is that Python data are typed and variables un-typed, moreover,
> he proposes that the terms "un-typed" and "uni-typed" are practically
> equivalent.
> At first it seemed somewhat reasonable to me, but the more I thought about
> it, the more my mind rejected both, the equivalence and the phrasing.
> The idea of uni-typing is that there's a set of types that the runtime
> supports and expressions can be composed of any members of that set, thus
> forming a single type, which is that set. This idea seems to describe the
> situation in a useful (for analysis) and an enlightening way, while the
> term "un-typed" does not seem to say anything useful.
> I'm also feeling uneasy about the phrasing: un-typed _variables_. That is,
> data and _expressions_ have types, but individual variables are just not
> something you can make a claim about outside of a context of an expression.
> We'd appreciate very much if the enlightened folks of this list would
> provide some input on this.
> --
> Siraaj Khandkar
> .o.  o.o  ..o  o..  .o.
> ..o  .oo  o.o  .oo  ..o
> ooo  .o.  .oo  oo.  ooo

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