A computational grammar and lexicon for Maltese

potentially be handled with dependent types on the abstract syntax level. However, since the
RGL abstract syntax is language-independent this would be not be possible without losing
some of this independence.
Incomplete inflection tables
It is often the case that certain slots in inflection tables simply do not exist in the language.
A prime example in Maltese is the dual form, which only a small number of nouns actually
have. When it exists, this form is used to replace both noun and determiner, e.g. xagħarejn
(‘two months’). For nouns with no dual form, one uses the numeral for ‘two’ together with
the plural form of the noun, e.g. żewġ fliexken (‘two bottles’). All objects of the same type must
have the same linearisation type in GF. So if the linearisation type for a noun contains a slot for
the dual form, what should this slot contain in the case of nouns with no dual?
The empty string "" would seem to be the logical choice, however this can create parsing
ambiguities if it is ever included in a linearisation. To prevent against this, syntax-level
functions need to be able to check whether a noun indeed supports the dual form or not. But
because of the limitations on runtime strings (described above), it is impossible to check, at
runtime, whether a string is the empty string or not. Attempting to use some garbage string
instead of the empty string does not help the situation at all, and adds the risk of appearing
in input completion. The solution to this is to store this information in some non-string field,
such as a boolean hasDual field, which can be consulted at runtime.
The Maybe type As this turned out to be a fairly common occurrence in the Maltese resource
grammar, a special Maybe type was defined as a generalisation of this programmatic idiom. This
type is defined as a type which takes another type as a parameter, as follows:
oper
Maybe : (t : Type) -> Type = \t -> {
inner : t ;
exists : Bool
} ;
Thus the type Maybe Str becomes a record containing a string and boolean field indicating
whether the former exists or not. This type and its supporting operations can be found in the
Maybe.gf module in the RGL’s prelude folder. An unfortunate downside to using the Maybe type
is that it causes a size explosion in the compiler when used in tables. This is explained below.
2.5.5 Parameters in tables
During the development of this resource grammar, it was discovered that using parameter
fields within tables will cause an exponential explosion in the GF compiler. Consider the following
example grammar:
concrete ParamConc of Param = open Prelude in {
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