Databases
StackOverflow2013
Postsdbo
POBNF: input going to wrong nonterminal
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POBNF: input going to wrong nonterminal
    primarykey
    data
    text
    <p>I'm developing a BNF for chess algebraic notation and ran into an interesting case, input going to the wrong non-terminal.</p> <p>My start BNF rule is as follows (note that this intentionally doesn't include castling or notes):</p> <pre><code>algebraic_notation : piece start_position capture end_position promotion </code></pre> <p><code>piece</code>, <code>start_position</code>, <code>capture</code>, and <code>promotion</code> can be empty, thus allowing for a move like 'd4'. The problem is that when such a move is entered, the input ('d4') is taken by <code>start_position</code>, thus resulting in an error b/c there is no more input for <code>end_position</code>, which cannot be empty.</p> <p>The obvious hack/workaround is to allow <code>end_position</code> to be empty and then check to see if we got any input for it and act accordingly.</p> <p>This does work, but I would like to know if there is a way to deal with this. Is it possible for input not to go to the first matching symbol if it causes the entire expression not to match?</p> <p>Another question is whether this is standard behaviour for BNF, or a problem with the yaccer I'm using: PLY v 3.3.</p> <p>Tried using flex/bison and got same thing. So it appears its not specific to PLY.</p> <p>Here are all the relevant rules for completeness:</p> <pre><code>algebraic_notation : piece start_position capture end_position promotion piece : KING | QUEEN | BISHOP | KNIGHT | ROOK | pawn pawn : empty start_position : FILE | NUMBER | FILE NUMBER | empty end_position : FILE NUMBER | empty // this line is the hack/workaround capture : CAPTURE | empty promotion : EQUAL QUEEN | EQUAL ROOK | EQUAL KNIGHT | EQUAL BISHOP | empty empty : </code></pre>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USMatthew
    1. USMatthew
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POBNF: input going to wrong nonterminal
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POBNF: input going to wrong nonterminal
      1. This table or related slice is empty.
      1. VTUpMod
    1. COIs yacc perhaps overkill for this problem?
      singulars
      1. POBNF: input going to wrong nonterminal
      1. USCam
    2. CO@cam Perhaps. But parsing strings by hand isn't all that clear or readable in my experience.
      singulars
      1. POBNF: input going to wrong nonterminal
      1. USMatthew
    3. COAlso, even if BNF is overkill for this particular application, its still possible to encounter this problem in a more complex grammar. Anyways, I have a workaround/hack; I merely that I want to use a better solution if possible.
      singulars
      1. POBNF: input going to wrong nonterminal
      1. USMatthew
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload