lisp-on-lines.lyx

   1 #LyX 1.3 created this file. For more info see http://www.lyx.org/
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   3 \textclass article
   4 \language english
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  16 \paperorientation portrait
  17 \secnumdepth 3
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  21 \quotes_language english
  22 \quotes_times 2
  23 \papercolumns 1
  24 \papersides 1
  25 \paperpagestyle default
  26
  27 \layout Title
  28
  29 LISP-ON-LINES
  30 \layout Author
  31
  32
  33 \noun on
  34 Drew Crapmsie
  35 \noun default
  36 ,
  37 \noun on
  38 José Pablo Ezequiel
  39 \begin_inset Quotes eld
  40 \end_inset
  41
  42 Pupeno
  43 \begin_inset Quotes erd
  44 \end_inset
  45
  46  Fernández Silva
  47 \layout Abstract
  48
  49
  50 \noun on
  51 Lisp-On-Lines
  52 \noun default
  53  is a very useful module that works on top of the
  54 \noun on
  55 UnCommon Web
  56 \noun default
  57  framework to do rapid developing of complex data-driven web appilcations
  58  (on
  59 \noun on
  60 Common Lisp
  61 \noun default
  62 , of course).
  63 \layout Section
  64
  65 Introduction
  66 \layout Standard
  67
  68
  69 \noun on
  70 Lisp-On-Lines
  71 \noun default
  72  was founded and developed and continues to be developed and mantained by
  73
  74 \noun on
  75 Drew Crapmsie
  76 \noun default
  77 .
  78 \layout Subsection
  79
  80 Conventions
  81 \layout Standard
  82
  83 The conventions used in this manual are:
  84 \layout Itemize
  85
  86 Dode is shown as a monospace font.
  87  When it is expected that the user is working in an interactive environment
  88  what the user should type appears as bold, while the computer result appears
  89  non-bold, for example:
  90 \begin_deeper
  91 \layout LyX-Code
  92
  93 >
  94 \series bold
  95 (+ 5 10)
  96 \layout LyX-Code
  97
  98 15
  99 \end_deeper
 100 \layout Itemize
 101
 102 Names of people or products are show as small caps, like
 103 \noun on
 104 Drew Crapmsie
 105 \noun default
 106  or
 107 \noun on
 108 Lisp-On-Lines
 109 \noun default
 110 .
 111 \layout Itemize
 112
 113 Sections marked with
 114 \color red
 115 ToDo
 116 \color default
 117  require further revision.
 118 \layout Standard
 119
 120
 121 \color red
 122 ToDo: Add more conventions as they are needed, possible classes of text:
 123  names of concepts, name of programming entities, like variables, functions,
 124  etc (which are embedded in text, should they be shown monospaced ?).
 125 \layout Section
 126
 127 Components
 128 \layout Description
 129
 130 Meta\SpecialChar ~
 131 Model\SpecialChar ~
 132 Protocol A Protocol for introspection on relational objects.
 133 \layout Description
 134
 135 Mewa\SpecialChar ~
 136 Presentations A Mewa-like
 137 \begin_inset Foot
 138 collapsed true
 139
 140 \layout Standard
 141
 142 http://www.adrian-lienhard.ch/files/mewa.pdf
 143 \end_inset
 144
 145  layer for UncommonWeb
 146 \begin_inset Foot
 147 collapsed true
 148
 149 \layout Standard
 150
 151 http://common-lisp.net/project/ucw/
 152 \end_inset
 153
 154  Presentations.
 155 \layout Section
 156
 157 Example
 158 \layout Standard
 159
 160 First we start with the data model.
 161  The Meta Model Protocol (MMP) is used to provide information on the data
 162  objects and how they relate to one another.
 163  Its is currently implemented as a layer over CLSQL
 164 \begin_inset Foot
 165 collapsed true
 166
 167 \layout Standard
 168
 169 http://clsql.b9.com/
 170 \end_inset
 171
 172 , although support is planned for other backends (
 173 \noun on
 174 CLOS
 175 \noun default
 176 ,
 177 \noun on
 178 Elephant
 179 \noun default
 180 [4], whatever).
 181 \layout Standard
 182
 183 The MMP shares its definition syntax with
 184 \emph on
 185 \noun on
 186 CLSQL
 187 \emph default
 188 \noun default
 189 's Object Oriented Data Definition Language (OODDL)
 190 \begin_inset Foot
 191 collapsed true
 192
 193 \layout Standard
 194
 195 http://clsql.b9.com/manual/ref-ooddl.html
 196 \begin_inset Note
 197 collapsed true
 198
 199 \layout Standard
 200
 201 Shouldn't this footnote be a bibliographical entry ? or something like that
 202  ?
 203 \end_inset
 204
 205
 206 \end_inset
 207
 208 .
 209  The macro to define view-classes is named DEF-VIEW-CLASS/META, and takes
 210  the same arguments as DEF-VIEW-CLASS from CLSQL.
 211  For the purposes of this simple example, we will only need two functions
 212  from the MMP beyond what CLSQL provides : LIST-SLOTS and LIST-SLOT-TYPES[5].
 213 \layout Standard
 214
 215 We'll define a simple class to hold a user.
 216 \layout LyX-Code
 217
 218 >
 219 \series bold
 220 (def-view-class/meta user ()
 221 \layout LyX-Code
 222
 223
 224 \series bold
 225    ((userid :initarg :userid :accessor userid :type integer :db-kind :key)
 226 \layout LyX-Code
 227
 228
 229 \series bold
 230     (username :initarg :username :accessor username :type string :db-kind
 231  :base)
 232 \layout LyX-Code
 233
 234
 235 \series bold
 236     (password :initarg :password :accessor password :type string :db-kind
 237  :base)))
 238 \layout Standard
 239
 240 and now we create a user:
 241 \layout LyX-Code
 242
 243 >
 244 \series bold
 245 (defparameter user (make-instance 'user :userid 1
 246 \layout LyX-Code
 247
 248
 249 \series bold
 250                                           :username "drewc"
 251 \layout LyX-Code
 252
 253
 254 \series bold
 255                                           :password "p@ssw0rd"))
 256 \layout Standard
 257
 258 We can see the slots of users running:
 259 \layout LyX-Code
 260
 261 >
 262 \series bold
 263 (lisp-on-lines::list-slots user)
 264 \layout LyX-Code
 265
 266 (USERID USERNAME PASSWORD)
 267 \layout Standard
 268
 269 or the types with:
 270 \layout LyX-Code
 271
 272 >
 273 \series bold
 274 (lisp-on-lines::list-slot-types user)
 275 \layout LyX-Code
 276
 277 ((USERID INTEGER) (USERNAME STRING) (PASSWORD STRING))
 278 \layout Standard
 279
 280 To see the default attributes of a class
 281 \begin_inset Marginal
 282 collapsed true
 283
 284 \layout Standard
 285
 286 Is this correct ? Drew, please, check.
 287 \end_inset
 288
 289  we run.
 290 \layout LyX-Code
 291
 292 >
 293 \series bold
 294 (lisp-on-lines::default-attributes user)
 295 \layout LyX-Code
 296
 297 ((USERID INTEGER :LABEL "USERID" :SLOT-NAME USERID)
 298 \layout LyX-Code
 299
 300  (USERNAME STRING :LABEL "USERNAME" :SLOT-NAME USERNAME)
 301 \layout LyX-Code
 302
 303  (PASSWORD STRING :LABEL "PASSWORD" :SLOT-NAME PASSWORD))
 304 \layout Standard
 305
 306 To set the attributes of a class to the default values we use:
 307 \layout LyX-Code
 308
 309 >
 310 \series bold
 311 (lisp-on-lines::set-default-attributes user)
 312 \layout LyX-Code
 313
 314 ((USERID INTEGER :LABEL "USERID" :SLOT-NAME USERID)
 315 \layout LyX-Code
 316
 317  (USERNAME STRING :LABEL "USERNAME" :SLOT-NAME USERNAME)
 318 \layout LyX-Code
 319
 320  (PASSWORD STRING :LABEL "PASSWORD" :SLOT-NAME PASSWORD))
 321 \layout Standard
 322
 323 which takes an object of the class we are working with.
 324  This is going to be change so we can do this action directly on the class.
 325  It is on the TODO file.
 326 \layout Standard
 327
 328 Class attributes?
 329 \layout LyX-Code
 330
 331 >
 332 \series bold
 333 (lisp-on-lines::find-class-attributes user)
 334 \layout LyX-Code
 335
 336 (USER (PASSWORD STRING :LABEL "PASSWORD" :SLOT-NAME PASSWORD)
 337 \layout LyX-Code
 338
 339       (USERNAME STRING :LABEL "USERNAME" :SLOT-NAME USERNAME)
 340 \layout LyX-Code
 341
 342       (USERID INTEGER :LABEL "USERID" :SLOT-NAME USERID)
 343 \layout LyX-Code
 344
 345       NIL)
 346 \layout Standard
 347
 348 note that the mewa functions (find-attribute, set-attribute etc) can take
 349  either an instance, or a class-name as a symbol:
 350 \layout LyX-Code
 351
 352 >
 353 \series bold
 354 (lisp-on-lines::find-class-attributes 'user)
 355 \layout LyX-Code
 356
 357 (USER (PASSWORD STRING :LABEL "PASSWORD" :SLOT-NAME PASSWORD)
 358 \layout LyX-Code
 359
 360       (USERNAME STRING :LABEL "USERNAME" :SLOT-NAME USERNAME)
 361 \layout LyX-Code
 362
 363       (USERID INTEGER :LABEL "USERID" :SLOT-NAME USERID)
 364 \layout LyX-Code
 365
 366       NIL)
 367 \layout LyX-Code
 368
 369 >
 370 \series bold
 371 (lisp-on-lines::find-class-attributes (make-instance 'user))
 372 \layout LyX-Code
 373
 374 (USER (PASSWORD STRING :LABEL "PASSWORD" :SLOT-NAME PASSWORD)
 375 \layout LyX-Code
 376
 377       (USERNAME STRING :LABEL "USERNAME" :SLOT-NAME USERNAME)
 378 \layout LyX-Code
 379
 380       (USERID INTEGER :LABEL "USERID" :SLOT-NAME USERID)
 381 \layout LyX-Code
 382
 383       NIL)
 384 \layout Standard
 385
 386 Using that information, we have enough to create an interface to the object.
 387
 388 \noun on
 389 UnCommon Web
 390 \noun default
 391  includes a powerful presentation system
 392 \begin_inset Foot
 393 collapsed true
 394
 395 \layout Standard
 396
 397 To see this system in action, we strongly recomend to study the presentations
 398  example which comes with
 399 \noun on
 400 UnCommon Web
 401 \noun default
 402 .
 403  Reading components/presentations.lisp can help understand a lot about how
 404  presentations are built.
 405 \end_inset
 406
 407 , but it is not dynamic enough for some of the most advanced applications.
 408  Mewa defines an approach to presentations that solves that problem, but
 409  the paper is written from a
 410 \noun on
 411 Smalltalk
 412 \noun default
 413  point of view.
 414  A mixture of the two , Mewa Presentations(MP), is described here.
 415 \layout Standard
 416
 417 MP introduces to
 418 \noun on
 419 UnCommon Web
 420 \noun default
 421  the concept of
 422 \emph on
 423 attributes
 424 \emph default
 425 .
 426  An attribute is essentially a named version of the DEFPRESENTATION slot-like
 427  arguments, for example in :
 428 \layout LyX-Code
 429
 430 >
 431 \series bold
 432 (defpresentation person-editor (object-presentation)
 433 \layout LyX-Code
 434
 435
 436 \series bold
 437    ((string :label "First Name" :slot-name 'first-name :max-length 30)))
 438 \layout Standard
 439
 440 the (string :label "First Name" ...) form is an attribute definiton.
 441  Attributes are accessed through FIND-ATTIRIBUTES, and are composed at run
 442  time (where the
 443 \noun on
 444 UnCommon Web
 445 \noun default
 446 's presentation system is done at compile time) to display the object.
 447  This allows a very flexible system of displaying objects which is reminiscent
 448  of
 449 \noun on
 450 CSS
 451 \noun default
 452
 453 \begin_inset Foot
 454 collapsed true
 455
 456 \layout Standard
 457
 458
 459 \noun on
 460 Drew Crapmsie
 461 \noun default
 462  discovered this, rather than invent or design it, so there are some rough
 463  edges, but its a good start.
 464 \end_inset
 465
 466 .
 467 \layout Standard
 468
 469 Its much easier to show this than to tell.
 470  Lets present our user class.
 471  Currently in
 472 \noun on
 473 UnCommon Web
 474 \noun default
 475 , you'd define a presentation as such :
 476 \layout LyX-Code
 477
 478 >
 479 \series bold
 480 (defpresentation user-presentation (object-presentation)
 481 \layout LyX-Code
 482
 483 ((INTEGER :LABEL "USERID" :SLOT-NAME USERID)
 484 \layout LyX-Code
 485
 486  (STRING :LABEL "USERNAME" :SLOT-NAME USERNAME)
 487 \layout LyX-Code
 488
 489  (STRING :LABEL "PASSWORD" :SLOT-NAME PASSWORD)))
 490 \layout Standard
 491
 492 which could be presented using PRESENT-OBJECT :
 493 \layout LyX-Code
 494
 495 >
 496 \series bold
 497 (present-object user :using 'user-presentation)
 498 \layout Standard
 499
 500 The equivalent approach using mewa presentations is actually longer and
 501  more verbose(!) but it serves to demonstrate how the MP system works.
 502 \layout Standard
 503
 504 Mewa Presentations adds a set of attributes to a class, keyed off the class
 505  name.
 506  Attributes are inherited, so if you define an attribute on T, you can use
 507  it with any class.
 508 \layout Standard
 509
 510 MP stores named attributes keyed on a class name.
 511  To achieve the same functionality as the above using mp would look like
 512  this :
 513 \layout LyX-Code
 514
 515 >
 516 \series bold
 517 (setf (lisp-on-lines::find-attribute 'user :viewer)
 518 \begin_inset Marginal
 519 collapsed true
 520
 521 \layout Standard
 522
 523 Isn't this too imperative (in contrast to functional, lispy).
 524 \end_inset
 525
 526
 527 \layout LyX-Code
 528
 529
 530 \series bold
 531         '(lisp-on-lines::mewa-object-presentation
 532 \layout LyX-Code
 533
 534
 535 \series bold
 536           :attributes (userid username password)
 537 \layout LyX-Code
 538
 539
 540 \series bold
 541           :global-properties (:editablep nil)))
 542 \layout LyX-Code
 543
 544 (:VIEWER MEWA-OBJECT-PRESENTATION
 545 \layout LyX-Code
 546
 547          :ATTRIBUTES
 548 \layout LyX-Code
 549
 550          (USERID USERNAME PASSWORD)
 551 \layout LyX-Code
 552
 553          :GLOBAL-PROPERTIES
 554 \layout LyX-Code
 555
 556          (:EDITABLEP NIL))
 557 \layout LyX-Code
 558
 559 >
 560 \series bold
 561 (setf (lisp-on-lines::find-attribute 'user 'userid)
 562 \begin_inset Marginal
 563 collapsed true
 564
 565 \layout Standard
 566
 567 Are this setfs to 'userid, 'username and 'password needed ? I (Pupeno) inspected
 568  they contents at of this moment and they seem to already contain what they
 569  are being set to.
 570 \end_inset
 571
 572
 573 \layout LyX-Code
 574
 575
 576 \series bold
 577         '(integer :label "userid" :slot-name userid))
 578 \layout LyX-Code
 579
 580 (USERID INTEGER :LABEL "USERID" :SLOT-NAME USERID)
 581 \layout LyX-Code
 582
 583 >
 584 \series bold
 585 (setf (lisp-on-lines::find-attribute 'user 'username)
 586 \layout LyX-Code
 587
 588
 589 \series bold
 590         '(STRING :LABEL "USERNAME" :SLOT-NAME USERNAME))
 591 \layout LyX-Code
 592
 593 (USERNAME STRING :LABEL "USERNAME" :SLOT-NAME USERNAME)
 594 \layout LyX-Code
 595
 596 >
 597 \series bold
 598 (setf (lisp-on-lines::find-attribute 'user 'password)
 599 \layout LyX-Code
 600
 601
 602 \series bold
 603         '(STRING :LABEL "USERNAME" :SLOT-NAME PASSWORD))
 604 \layout LyX-Code
 605
 606 (PASSWORD STRING :LABEL "USERNAME" :SLOT-NAME PASSWORD)
 607 \layout LyX-Code
 608
 609 >
 610 \series bold
 611 (lisp-on-lines::find-class-attributes 'user)
 612 \layout LyX-Code
 613
 614 (USER
 615 \layout LyX-Code
 616
 617  (:VIEWER MEWA-OBJECT-PRESENTATION
 618 \layout LyX-Code
 619
 620           :ATTRIBUTES
 621 \layout LyX-Code
 622
 623           (USERID USERNAME PASSWORD)
 624 \layout LyX-Code
 625
 626           :GLOBAL-PROPERTIES
 627 \layout LyX-Code
 628
 629           (:EDITABLEP NIL))
 630 \layout LyX-Code
 631
 632  (PASSWORD STRING :LABEL "PASSWORD" :SLOT-NAME PASSWORD)
 633 \layout LyX-Code
 634
 635  (USERNAME STRING :LABEL "USERNAME" :SLOT-NAME USERNAME)
 636 \layout LyX-Code
 637
 638  (USERID INTEGER :LABEL "USERID" :SLOT-NAME USERID)
 639 \layout LyX-Code
 640
 641  NIL)
 642 \layout Standard
 643
 644 this is all turned into a
 645 \noun on
 646 UnCommon Web
 647 \noun default
 648  presentation at runtime using MAKE-PRESENTATION, for example, the following
 649  code should be enough to show what's built so far attached to the examples
 650  application:
 651 \layout LyX-Code
 652
 653 >
 654 \series bold
 655 (defcomponent lol-example (window-component)
 656 \layout LyX-Code
 657
 658
 659 \series bold
 660    ())
 661 \layout LyX-Code
 662
 663 >
 664 \series bold
 665 (defmethod render-on ((res response) (lol-example lol-example))
 666 \layout LyX-Code
 667
 668
 669 \series bold
 670     (<:h1 "User")
 671 \layout LyX-Code
 672
 673
 674 \series bold
 675     (<ucw:render-component :component (lisp-on-lines::make-presentation
 676  user :type :viewer)))
 677 \layout LyX-Code
 678
 679 >
 680 \series bold
 681 (defentry-point "lol.ucw" (:application *example-application*) ()
 682 \layout LyX-Code
 683
 684
 685 \series bold
 686     (call 'products-presentation))
 687 \layout Standard
 688
 689 As you'll see, nothing is exported from the LISP-ON-LINES package.
 690  If you wish to use LOL in your own package (or in UCW-USER or whatever),
 691  you simply need to use the MEWA and META-MODEL packages.
 692 \layout Standard
 693
 694 SET-ATTRIBUTE can be used in place of (setf (find-attribute)) when you want
 695  to "inherit" the properties of an existing attribute definition :
 696 \layout Standard
 697
 698 LISP-ON-LINES> (set-attribute 'user 'password '(string :label "password:
 699  (must be at leat 8 chars)"))
 700 \layout Standard
 701
 702 (PASSWORD STRING
 703 \layout Standard
 704
 705 :LABEL
 706 \layout Standard
 707
 708 "password: (must be at leat 8 chars)"
 709 \layout Standard
 710
 711 :SLOT-NAME
 712 \layout Standard
 713
 714 PASSWORD)
 715 \layout Standard
 716
 717 Now we want to create a presentation with which to edit the username.
 718  we will use the existing attributes on a subclass of mewa-object-presetation
 719  :
 720 \layout Standard
 721
 722 LISP-ON-LINES> (defcomponent user-editor (mewa-object-presentation)
 723 \layout Standard
 724
 725 ()
 726 \layout Standard
 727
 728 (:default-initargs
 729 \layout Standard
 730
 731 :attributes '((username :label "Enter your New Username") password)
 732 \layout Standard
 733
 734 :global-properties '(:editablep t)))
 735 \layout Standard
 736
 737 USER-EDITOR
 738 \layout Standard
 739
 740 LISP-ON-LINES> (setf (find-attribute 'user :editor) '(user-editor))
 741 \layout Standard
 742
 743 (:EDITOR USER-EDITOR)
 744 \layout Standard
 745
 746 LISP-ON-LINES>
 747 \layout Standard
 748
 749 which we then can display below our earlier example :
 750 \layout Standard
 751
 752 (defmethod render-on ((res response) (e presentations-index))
 753 \layout Standard
 754
 755 "
 756 \layout Standard
 757
 758 As you'll see, nothing is exported from the LISP-ON-LINES package.
 759
 760 \layout Standard
 761
 762 if you wish to use LOL in your own package (or in UCW-USER or whatever),
 763 \layout Standard
 764
 765 you simply need to use the MEWA and META-MODEL packages"
 766 \layout Standard
 767
 768 (<ucw:render-component :component (lisp-on-lines::make-presentation lisp-on-line
 769 s::user :type :viewer))
 770 \layout Standard
 771
 772 (<ucw:render-component :component (lisp-on-lines::make-presentation lisp-on-line
 773 s::user :type :editor)))
 774 \layout Standard
 775
 776 that should give you some idea on how it works ..
 777  ask me when you get confused :)
 778 \layout Section
 779
 780 Pupeno's Example
 781 \layout Standard
 782
 783 This is Pupeno's view of how to do rapid developing of a database-driven
 784  web application.
 785  It currently is going to assume a very specific case but latter it may
 786  be made bigger.
 787 \layout Standard
 788
 789 We first start with a
 790 \noun on
 791 PostgreSQL
 792 \noun default
 793  connection of CLSQL which is set up with one line:
 794 \layout LyX-Code
 795
 796 >
 797 \series bold
 798 (clsql:connect '("localhost" "geo" "geo" "geogeo"))
 799 \layout Standard
 800
 801 which connect us to the server on
 802 \family typewriter
 803 localhost
 804 \family default
 805 , to the database
 806 \family typewriter
 807 geo
 808 \family default
 809  as user
 810 \begin_inset Quotes eld
 811 \end_inset
 812
 813 geo
 814 \begin_inset Quotes erd
 815 \end_inset
 816
 817  with password
 818 \begin_inset Quotes eld
 819 \end_inset
 820
 821 geogeo
 822 \begin_inset Quotes erd
 823 \end_inset
 824
 825  (this is not a smart way to generate password, don't do this).
 826  To have a nice SQL environment, we also want:
 827 \layout LyX-Code
 828
 829 >
 830 \series bold
 831 (clsql:locally-enable-sql-reader-syntax)
 832 \layout LyX-Code
 833
 834 >
 835 \series bold
 836 (setf clsql:*default-caching* nil)
 837 \layout Standard
 838
 839 Actually, it is more than a nice environmnet, without those lines the rest
 840  of the code won't work.
 841 \layout Standard
 842
 843 On the
 844 \family typewriter
 845 geo
 846 \family default
 847  database, there's a table called
 848 \family typewriter
 849 product
 850 \family default
 851  which has the following structure:
 852 \layout LyX-Code
 853
 854
 855 \series bold
 856 CREATE TABLE product (
 857 \layout LyX-Code
 858
 859
 860 \series bold
 861     id serial NOT NULL,
 862 \layout LyX-Code
 863
 864
 865 \series bold
 866     name text NOT NULL,
 867 \layout LyX-Code
 868
 869
 870 \series bold
 871     details text,
 872 \layout LyX-Code
 873
 874
 875 \series bold
 876     description text,
 877 \layout LyX-Code
 878
 879
 880 \series bold
 881     cost double precision,
 882 \layout LyX-Code
 883
 884
 885 \series bold
 886     CONSTRAINT product_cost_check CHECK ((cost > (0)::double precision))
 887 \layout LyX-Code
 888
 889
 890 \series bold
 891 );
 892 \layout LyX-Code
 893
 894
 895 \series bold
 896 ALTER TABLE ONLY product ADD CONSTRAINT product_name_key UNIQUE (name);
 897 \layout LyX-Code
 898
 899
 900 \series bold
 901 ALTER TABLE ONLY product ADD CONSTRAINT product_pkey PRIMARY KEY (id);
 902 \layout Standard
 903
 904
 905 \color red
 906 ToDo: express the table structure in a better way.
 907 \layout Standard
 908
 909 Now we'll create the class that represents a product, mirroring the database
 910  structure:
 911 \layout LyX-Code
 912
 913 >
 914 \series bold
 915 (lisp-on-lines::def-view-class/table "product")
 916 \layout Standard
 917
 918 and then we generate the default attributes (from
 919 \family typewriter
 920 product
 921 \family default
 922 's slots) and assign it to
 923 \family typewriter
 924 product
 925 \family default
 926 :
 927 \layout LyX-Code
 928
 929 >
 930 \series bold
 931 (lisp-on-lines::set-default-attributes (make-instance 'product))
 932 \begin_inset Marginal
 933 collapsed true
 934
 935 \layout Standard
 936
 937 set-default-attributes is marked to be renamed to set-generated-attributes.
 938 \end_inset
 939
 940
 941 \layout Standard
 942
 943 As you can see, we instantiate
 944 \family typewriter
 945 product
 946 \family default
 947  to pass it to
 948 \family typewriter
 949 set-default-attributes
 950 \family default
 951 , because it expects an object instead of a class.
 952  We don't need the object anymore, so we don't save any reference to it.
 953  In the future we might have a
 954 \family typewriter
 955 set-default-attributes
 956 \family default
 957  that can use a class directly.
 958  Now we set a the attribute
 959 \family typewriter
 960 :viewer
 961 \family default
 962  to contain the
 963 \family typewriter
 964 mewa-object-presentation
 965 \family default
 966  exposing the attributes we like the user to work with:
 967 \layout LyX-Code
 968
 969 >
 970 \series bold
 971 (setf (lisp-on-lines::find-attribute (make-instance 'product) :viewer)
 972 \layout LyX-Code
 973
 974
 975 \series bold
 976         '(lisp-on-lines::mewa-object-presentation
 977 \layout LyX-Code
 978
 979
 980 \series bold
 981           :attributes (name details description cost)
 982 \layout LyX-Code
 983
 984
 985 \series bold
 986           :global-properties (:editablep nil)))
 987 \layout Standard
 988
 989 The last parameter shows that it is not editable, which makes sense for
 990  a viewer.
 991 \the_end