\DOC

\TYPE {thytype_abbrev : {Name:string,Thy:string} * hol_type * bool -> unit}

\SYNOPSIS
Abbreviates a type to a specific theory-qualified name.

\KEYWORDS
Parsing, pretty-printing.

\DESCRIBE
A call to {thytype_abbrev({Name=n,Thy=t}, ty, prp)} establishes the
``kernel'' name {t$n} as an abbreviation for the type {ty}, as happens
with {type_abbrev}. The boolean flag {prp} indicates whether or not
this abbreviation will also be used when the printer comes to print
the given type. In other words, after the call it becomes possible to
write {``:args t$n``} to stand for type {ty}. If there are type
variables in {ty} they become the parameters to the new abbreviated
type operator. These parameters need to be filled in in the {args}
position above. If there are no type variables in {ty} then
abbreviation is of a whole type, and {args} must be blank.

If there was an existing abbreviation for {t$n}, then this will be
replaced by the call.

In addition, after the given call, this abbreviation will become the
preferred binding for the bare name {n}. Other abbreviations in
different theories will need to use the form with fully-qualified
names ({thy1$n}, {thy2$n} etc).

If the boolean flag is false, this invocation is comparable to the
behaviour after {intputonly_type_abbrev}: the abbreviation can be used
to input types of the desired pattern, but such types will print as
they did previously.

\FAILURE
Fails if {ty} is a variable type.

\COMMENTS
As with other parsing and pretty-printing functions, there is a
companion function, {temp_thytype_abbrev}, which has the same effect
on the global grammar but does not cause the change to persist when
the theory is exported.

It is legitimate to use a string for the theory component of the
record that does not correspond to the current theory. Indeed, it is
perfectly reasonable to do this, if one wants to give priority to a
particular ancestral abbreviation.

\SEEALSO
Parse.type_abbrev.

\ENDDOC