via LtU:
Just for me to remember, I reiterate some type theory terminology.
- statically checked
- statically typed
- typed
-
Each term of a language can be classified as being of at least one
(possibly more) sort (syntactic type).
Statically checked programs are safe in the sense that operations
are (statically) guaranteed to work only on sorts they are
intended for.
Examples: Alice,
Haskell,
O'Caml,
Standard ML
- unityped
- untyped
-
Special case of a typed language with only a single sort,
the universal sort, which is assigned to each term.
One implication is that not many interesting
assertions about unityped programs can be made statically.
Examples:
Common-Lisp,
Erlang,
Mozart/Oz,
Scheme,
Smalltalk,
Assembler
XXX This is not entirely true for some implementations of
those languages. They define subsorts (subtypes) of
the universal sort and function types which allows type
inference to some extent.
XXX Also, how do function types (cue word simply typed)
fit in there?
- dynamically checked
- tagged
-
All values are tagged.
Operations at run-time are constrained (by tags) to only work on
values they are intended for.
A program of a tagged language is safe in the sense that
violations of these constraints at run-time will not go
undetected.
Examples:
Common-Lisp,
Erlang,
Mozart/Oz,
Scheme,
Smalltalk
(Note how these overlap with unityped languages!)
- unsound
- unsafe
-
Languages which admit programs for which undefined behavior goes
undetected, for example, operations being applied to values they are not
defined for without raising an error.
Examples: C, Assembler
Other commonly heard terminology:
- strongly typed
-
Term better avoided, denoting a sound type system (as opposed to
unsound or none at all) and is applied to
statically checked or sometimes even dynamically
checked languages.
- weakly typed
-
Bad term for language with unsound type system.
- dynamically typed
- latently typed
-
Terms better avoided because they don't really mean types
in the narrow mathematical sense.
Both terms are used to mean the same as dynamically checked.
If anyone spots a mistake or can suggest better wording, do not
hesitate to contact me!
