[developers] Questions on the syntax of TDL

[Bernd Kiefer]

Concerning question 3, at least in TDL and PET there was no such 
restriction,
but that could make the definition of docstrings easier.

Best,

Bernd

On 11.07.2018 03:01, Michael Wayne Goodman wrote:
> I attempted to define a BNF-like description of TDL syntax on the 
> wiki: http://moin.delph-in.net/TdlRfc
> I tried to follow the partial BNF in the LKB source and often referred 
> to the lisp code itself in order to fill out the rest of the description.
>
> My 3 questions above are concisely repeated at the bottom of the wiki 
> along with some others.
>
> I welcome corrections and discussion (here or on the wiki) from any 
> TDL nerds or authorities (especially if you've written a TDL parser).
>
> On Mon, Jul 9, 2018 at 12:49 PM, Michael Wayne Goodman 
> <goodmami at uw.edu <mailto:goodmami at uw.edu>> wrote:
>
>     Hi developers,
>
>     I'm taking a closer look at the syntax of TDL files and the
>     situation is a bit of a mess. Can anyone help me clarify some
>     things? (I'll restrict myself to 3 questions for now)
>
>     The Copestake 2002 reference (Implementing TFS Grammars) has a BNF
>     for TDL, but it's a bit out of date and, according to comments in
>     the LKB source code, incorrect in parts. The LKB source comments
>     are scattered, incomplete, inconsistent, and also a bit outdated.
>     There is not much on the wiki. There is some discussion in the
>     mailing list archives (much from before my time in DELPH-IN), but
>     it's not clear how current those descriptions are.
>
>     Q1: Are supertypes special in a definition?
>
>     The BNF (in the LKB source) says this:
>
>         Type-def -> Type { Avm-def | Subtype-def} . |
>                              Type { Avm-def | Subtype-def}.
>         Avm-def -> := Conjunction | Comment Conjunction
>         Conjunction -> Term { & Term } *
>         Term -> Type | Feature-term | Diff-list | List | Coreference
>
>     That makes it sound like I could do this:
>
>         mytype := [ FEAT val ] & supertype.
>
>     or even:
>
>         mytype := <! diff list.. !> & #coref & supertype.
>
>     But elsewhere it seems like a list of parents is special and
>     appears before the rest of the conjunction. E.g., at
>     read-tdl-avm-def of lingo/lkb/src/io-tdl/tdltypeinput.lsp I see
>     this alternate definition of Avm-def:
>
>       ;;; Avm-def -> := Parents Conjunction | Parents Comment
>     Conjunction |
>       ;;;               Parents | Parents Comment
>
>     It seems that both ACE and PET are fine with putting supertypes
>     after the feature list (and some other variations). I'm fine with
>     this, but I wonder what it means for docstrings (see Q3 below),
>     which (I think) are supposed to appear after the list of parents
>     and before the feature list.
>
>
>     Q2: Subtype-def is now just a variant of Avm-def, yes?
>
>     The BNF still describes subtyping (with the :< operator) as only
>     taking a single parent:
>
>         Subtype-def ->  :< type
>
>     But I believe the consensus is that this is unnecessary (it's
>     equivalent to using := with only a supertype), so :< is treated as
>     equivalent to := (to avoid breaking backward compatibility). Is
>     this interpretation used by all processors?
>
>
>     Q3: What's the final word with type comments / docstrings?
>
>     I find evidence of 3 proposed variants: (1) a block of ";"
>     comments before a typename (LTDB-style); (2) a block of ";"
>     comments within a type description; and (3) a "doc string" within
>     a type description. Furthermore, there is a question as to whether
>     comments or strings within a type go after the ":=" or after the
>     list of supertypes. I think #| ... |# comments were not considered
>     for this purpose.
>
>     My guess is this:
>
>     * LTDB-style comments (before the type identifier) are processed
>     separately from TDL-parsing
>     * type-internal comments can go anywhere but are discarded
>     * type-internal doc strings must appear after the list of
>     supertypes and are later available for inspection (they are
>     included as a non-functional part of a type)
>
>     ACE seems happy with my assumptions, although PET doesn't seem to
>     like doc strings at all.
>
>
>     Thanks!
>
>     -- 
>     Michael Wayne Goodman
>
>
>
>
> -- 
> Michael Wayne Goodman

-- 
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