Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Are you already familiar with <a href="http://en.wikipedia.org/wiki/Recursive_descent_parser" rel="noreferrer">recursive descent parsers</a>? They're relatively easy to write by hand in your favourite programming language, which would include Emacs Lisp. For very simple parsing, you can often get by with <code>looking-at</code> and <code>search-forward</code>. These would also form the basis of any <a href="http://en.wikipedia.org/wiki/Lexical_analysis" rel="noreferrer">tokenizing</a> routines that would be called by your recursive descent parser, or any other style of parser.</p> <p><strong>[11 Feb 2009]</strong> I added an example recursive descent parser in emacs lisp below. It parses simple arithmetic expressions including addition, subtraction, multiplication, division, exponentiation, and parenthesized sub-expressions. Right now, it assumes all tokens are in the global variable <code>*tokens*</code>, but if you modify <code>gettok</code> and <code>peektok</code> as necessary you can have them walk through a buffer. To use it as is, just try out the following:</p> <pre><code>(setq *token* '( 3 ^ 5 ^ 7 + 5 * 3 + 7 / 11)) (rdh/expr) =&gt; (+ (+ (^ 3 (^ 5 7)) (* 5 3)) (/ 7 11)) </code></pre> <p>The parsing code follows.</p> <pre><code>(defun gettok () (and *token* (pop *token*))) (defun peektok () (and *token* (car *token*))) (defun rdh/expr () (rdh/expr-tail (rdh/factor))) (defun rdh/expr-tail (expr) (let ((tok (peektok))) (cond ((or (null tok) (equal tok ")")) expr) ((member tok '(+ -)) (gettok) (let ((fac (rdh/factor))) (rdh/expr-tail (list tok expr fac)))) (t (error "bad expr"))))) (defun rdh/factor () (rdh/factor-tail (rdh/term))) (defun rdh/factor-tail (fac) (let ((tok (peektok))) (cond ((or (null tok) (member tok '(")" + -))) fac) ((member tok '(* /)) (gettok) (let ((term (rdh/term))) (rdh/factor-tail (list tok fac term)))) (t (error "bad factor"))))) (defun rdh/term () (let* ((prim (rdh/prim)) (tok (peektok))) (cond ((or (null tok) (member tok '(")" + - / *))) prim) ((equal tok '^) (gettok) (list tok prim (rdh/term))) (t (error "bad term"))))) (defun rdh/prim () (let ((tok (gettok))) (cond ((numberp tok) tok) ((equal tok "(") (let* ((expr (rdh/expr)) (tok (peektok))) (if (not (equal tok ")")) (error "bad parenthesized expr") (gettok) expr))) (t (error "bad prim"))))) </code></pre>
    singulars
    1. This table or related slice is empty.
    1. POParsing in Emacs Lisp
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USDale Hagglund
    1. USDale Hagglund
    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. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COI found the recursive descent parsers page earlier. To bad the c-example wasn't complete so that I could test it though. But I guess this is a good way to do the parser in my case. Do you know of any Lisp example?
      singulars
      1. PO
      1. USrejeep
    2. COI don't know of any particular lisp examples, I'm afraid, but as far as I could tell all that's missing from the example is the tokenizing routines.
      singulars
      1. PO
      1. USDale Hagglund
    3. CODon't know almost any c, so it would have been a lot better if the example was working from scratch. But I'll google for other examples. Thanks!
      singulars
      1. PO
      1. USrejeep
 

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