Below a number of edge cases for slif grammars where I am not sure
about the legality. IOW if any of them are errors or not. And in the
latter case the behaviour of Marpa.
(1) = = == === ===== ======== =============
:start ::= A
A ~ 'a'
= = == === ===== ========
Is A a lexeme ?
Is a lexeme allowed as the G1 start symbol ?
(2) = = == === ===== ======== =============
A ::= B C
B ~ 'b'
C ~ 'aa' B
= = == === ===== ========
A is a G1 symbol.
B is a lexeme.
Is C a lexeme ?
Is it allowed to use a lexeme on the RHS of a match rule ?
(3) = = == === ===== ======== =============
A ::= B C
B ~ 'b'
C ~ B
= = == === ===== ========
A variant of (2) where C is reduced to be an alias of B.
Does that change the answers ?
(4) = = == === ===== ======== =============
X ::= B
B ~ 'bb' A
A ~ 'a'
discard ~ A
= = == === ===== ========
A is both used as discard, and on the RHS of the lexeme B.
Is that allowed ? What if B is not a lexeme ?
(5) = = == === ===== ======== =============
X ::= B
B ~ A
A ~ 'a'
discard ~ A
= = == === ===== ========
A variant of (4) where the regular match B was reduced to be
an alias of the discard match.
(6) = = == === ===== ======== =============
X ::= B
B ~ 'a'
A ~ 'a'
discard ~ A
= = == === ===== ========
And a variant of (5, 6) where the symbols are definitely
separate, but the underlying definitions are structurally
identical.
This could also be written as
= = == === ===== ======== =============
X ::= B
B ~ 'a'
discard ~ 'a'
= = == === ===== ========
--
See you,
Andreas Kupries <[email protected]>
<http://core.tcl.tk/akupries/>
Developer @ SUSE
Tcl'2017, Oct 16-20, Houston, TX, USA. http://www.tcl.tk/community/tcl2017/
EuroTcl 2017, Jul 8-9, Berlin/DE, http://www.eurotcl.tcl3d.org/
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