A computational grammar and lexicon for Maltese

2.5.2 Binding of runtime tokens
Binding is a solution to the fact that (i) GF does not allow gluing suffixes to tokens at runtime,
and (ii) storing hundreds or thousands of inflection forms in a table becomes very inefficient
in terms of the time and space required to compile to PGF. This solution works by introducing
a special bind token &+ in between tokens which should be linearised as a single word during
unlexing. This process of unlexing is deterministic and simple.
However, the lexing process — which requires the re-insertion of the bind token between
stems and suffixes — can be problematic. Since this lexing must occur as a pre-processing step
before input to the runtime, the lexer must essentially work without any access to the grammar
rules defined in the GF modules. This means that without re-implementing potentially large
parts of the morphological rules in an discrete lexer, ambiguities may arise. In Maltese for
example, the suffix -u may be an enclitic pronoun indicating possession on a noun, e.g. qalbu
(‘his heart’), as well as a regular conjugational ending of a verb: e.g. talbu (‘they prayed’). The
former is composed of the stem qalb and the pronominal suffix -u, which should be lexed into
tokens ["qalb","&+","u"]. However a naïve external lexer may also try to lex talbu in the same
way, which would be incorrect.
Thus is it clear that any lexing process must have at least some knowledge of the grammar
itself, although the current GF implementation has no real support for this. As a result, without
further developments in the runtime, this resource grammar is of very limited use for parsing.
The same is true of other resource grammars which using this binding solution.
2.5.3 Pattern matching on runtime strings
The inability to pattern match or perform any query operations on strings at runtime can have
a big effect on the design of a grammar. This becomes especially evident when stem changes
occur during affixation, often referred to as Sandhi. In Maltese for example, the verb fetħet
(‘she opened’) undergoes a vowel change from e → i when suffixed by an enclitic pronoun -
hom to become fetħithom (‘she opened them’). The joining of verb stems and suffixes occurs at
the syntax level, for example in the ComplSlash function from the VerbMlt module. Yet by this
point it is too late to analyse the verb stem and perform any required vowel changes. Instead,
all possible verb stems must be computed within the morphological paradigm and stored in
its inflection table. The selection of the correct stem must then be based on some other criteria,
such as parameter values.
2.5.4 Non-existent forms
Partial functions
All functions in GF must be total; for example, if the function PassV2 has type signature V2 ->
VP then it must be defined for any term of type V2. It is possible to imagine situations where
no passive verb phrase can be constructed out of a certain 2-place verb. Yet it is not possible to
implement PassV2 in such a way that it may only defined for some terms of type V2. This could
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