Screen Editor and Frame-Up on the MIT Lisp Machine and Genera

Complete command comparison

System 46 contains 13 entries. System 303 adds Create (expand) and Attributes, moves Exit to the last position, supplies item-specific mouse documentation for all 15 items, and styles Exit as standout. Genera retains the same 15 operations but places Exit and Undo before the geometry group and gives the pop-up a Screen Edit Operation label.

Move Multiple and Move Single

These two commands expose behavior that a short menu label cannot convey.

Move Multiple treats window boundaries as connected geometry. A Left click on an edge or corner toggles it in the move set; selecting one member of a group of coincident features includes the others so adjacent windows can remain joined. A second click removes an unwanted member. Releasing Left at 60 ticks or earlier is a short toggle; remaining held when elapsed time becomes greater than 60 toggles and starts the move. In System 303 and Genera, Right alone starts the current set without toggling and either Left or Right can fix the group; Middle cancels. System 46 requires Left to start and finish and treats Middle or Right as cancel. An outside click is not universally ignored: the C46 Multiple path and the C46/C303 Single paths feed the source's :OUT descriptor to an invalid feature operation and can signal, whereas Genera releases outside clicks and continues.

Move Single uses a large arrow cursor. At an edge it points perpendicular to the edge; at a corner it rotates to keep pointing at that corner. Once selected, the feature follows the pointer until placed. In System 303 and Genera the initial Right cancels, while a final Right commits because only Middle is rejected at placement; System 46 rejects Right at both stages. Maintained System 303 and Genera validate proposed edges centrally, beeping and reporting an illegal result while continuing with later records. System 46 sends proposed edges directly, leaving acceptance or a condition to the target window's edge-setting behavior.

Pointer sampling is also release-visible. C46 Move Window waits for button release and then reads the release position; System 303 records mask and position at button-down and returns while it is held. In the older two-corner Reshape, the first corner uses the release-time position. For the second, C46 waits for a nonzero mask without retaining its identity, while System 303 retains the mask; both perform blinker cleanup and then read the still-live coordinates without awaiting release. The sampled lower-right x and y are incremented for half-open edges. Move Window and older Reshape can validate once in their tracking helper and again, or directly set, during central application, so a stateful target can accept the first stage and reject or signal at the second.

System 303's Right smart corner is an order-sensitive snap, not a nearest-edge search. It walks the entire exposed sheet hierarchy in depth-first postorder, including nested descendants and finally the edited sheet, tests low then high edges on each axis for each sheet, lets later qualifying edges overwrite earlier ones, and finally clamps x and y inclusively to the edited sheet's low and high inside-coordinate bounds.

What Undo really stores

The Screen Editor does not record an inverse function for every command. It snapshots each editable inferior as:

(window exposed-state left top right bottom)

Commands return a transformed list, and the central loop applies the geometric and exposure side effects. This makes ordinary geometry changes reversible with one saved prior list. System 303 and Genera reread the live screen immediately before a command so changes made by other processes or by screen management are incorporated. Only a command that returns the literal abort sentinel preserves the prior Undo history. Reshape cancellation, Move Multiple/Single cancellation, System 303 Attributes Abort, and other successful unchanged results can consume the preceding Undo opportunity. System 46 has no sentinel, so even a canceled initial selection normally replaces history with the unchanged state.

System 46 snapshots only at entry and after application, but “stale snapshot” is not its whole command contract. Hit-testing, Bury/Expose, Move Multiple/Single, and Expand All use stored rows; Move Window and Reshape reread live target geometry, Expand Window rereads live superior/siblings/geometry, and object menus or destructive commands query live objects. Concurrent changes can therefore be stale, fresh, or mixed depending on the operation.

The source also records exact limits:

• Kill cannot be undone because the window object has been destroyed.
• Undo has no object-destruction or resurrection operation. Comments/manual wording expect a created object to remain buried, but the apply loop has no explicit action for an object absent from the old snapshot, while later menu documentation says Create and Kill cannot be undone. The exact runtime result remains open.
• Reconstructing the precise order of deexposed inferiors is not always possible. Undoing an exposure can therefore return a window to the wrong place in that hidden ordering.
• For the same reason, two successive Undo operations are not guaranteed to be a no-op, and undoing the bury of an already deexposed window is inexact.

These are implementation comments and behaviors, not retrospective guesses.

Attribute editing changed from a fixed form to delegation

System 303's Attributes command builds a fixed variable-value editor. It first probes border, label, and name capabilities in that order, sends ten unconditional base getters, then sends the supported name-or-label, border, and border-margin getters; font-map retrieval occurs while the form is constructed. It offers:

• current font;
• **MORE** processing;
• reverse video and vertical line spacing;
• actions for input and output attempted while deexposed;
• an always-visible Other output-action S-expression;
• character-drawing and erasing ALU functions;
• screen-manager priority and save-bits behavior;
• window name or label; and
• border width and border-margin width.

The form has Done and Abort choices. Changing reverse video also updates the default draw and erase ALU operations so their polarity remains coherent. Choice rows respond only to exact unmodified single Left or Right. The TV encoder chooses the highest newly-down button, so a simultaneous chord containing Right takes the Right row path, Left+Middle becomes the no-action Middle path, and sequential presses remain separate events. Modifier-bearing and multiple-click row events do not match; byte-exact MOUSE-3-2—whether Shift+single Right or natural double-Right produced it—is intercepted for the System Menu.

Typed rows use Left for an empty replacement and Right for the printed old value with point at its beginning. They do not use Genera's Input Editor. They enter System 303's native alternate rubout handler, whose complete 36-entry base map includes character/word/S-expression motion and deletion, mark/kill/yank histories, four Help forms, decimal numeric arguments, and the C-Q quote-next prefix. Emptying the buffer starts a second-stage handshake: another Rubout restores the old value; another character is put back and starts a fresh empty retry. Number, S-expression, and string rows then use distinct readers. Reader parse errors remain inside the editor for correction, while an escaping type error uses the form's one-character dismissal/put-back retry loop. The complete key/argument/pointer tree is in the reimplementation specification. The temporary form also saves and selects over the prior window, then unconditionally reselects that saved non-NIL object during cleanup. Thus a selection made through System Menu while Attributes is active can be overridden when the form exits; the source has no dead-saved-window guard.

Genera replaces that hard-coded catalog with a protocol. The Screen Editor asks the selected window for its own attribute queries and applies the returned message/value pairs. This lets different window classes expose different editable attributes without changing the Screen Editor itself. Its Accepting Values form has a separate idle accelerator map (Refresh, Help, End, Abort, Space, C-E, C-D, and C-N/C-P/C-F/C-B), Standard Scrolling and Standard Arguments prefix trees, exact Left/Middle/Shift-Middle pointer handlers, and generic Right operation menus. Entering a field then changes context to the full Input Editor and type-specific completion map; idle unknown keys are accelerator errors, not self-insertion.

Source-only lineage findings

The Genera code is recognizably descended from the MIT implementation: the operation names, edge-alist transaction model, :BURY marker, expansion algorithms, following arrow, and Undo caveats remain. It is not merely a new tool with a reused name.

The later implementation is nevertheless adapted to Genera's multi-console window environment. It obtains the mouse, selected window, and who line from the edited sheet's console; considers an ancestor editable only when it advertises editable inferiors; uses the Genera window reshaper; and delegates attribute selection to the window. This is a concrete example of old Lisp Machine UI machinery surviving while its protocols evolved.

Complete Frame-Up command inventory

Frame-Up itself requests no single-character keyboard accelerators. All ten commands are available by name through its Command Processor and as menu choices. Its title pane displays Layout for program <program>; configuration-name title text exists only as commented source.

No base Frame-Up keybinding is installed for these commands. :MENU-ACCELERATOR T marks their menu role; it is not a character binding. Its local command table inherits from no other command table and explicitly disables accelerator reading. The interactor instead reads a typed command name: ordinary graphics insert text; Space/Line delimit, Complete/Tab/Super-Complete complete, Meta-Complete previews or acquires arguments, Help/C-?/C-/ describe possibilities, and Return/C-Return/End activate a valid command. The complete Input Editor map remains active underneath that per-call parser context, including its numeric arguments and C-Q and scroll register second stages; those arguments edit input and do not repeat Frame-Up commands. Abort and Suspend families retain their stream/process meanings.

Left and Shift-Left over a leaf request horizontal and vertical Split respectively; Middle requests Set Pane Options. Right opens the generic presentation Operation menu. Set Pane Name and Delete Pane have no direct gesture and are menu-only presentation translators; the Split translators are menu candidates as well. The complete menu-button argument-acquisition and presentation tree is recorded in the reimplementation specification.

Pointer matching is exact, not “button present.” The Dynamic Windows encoder has 32 modifier states for each of three buttons. Frame-Up therefore distinguishes 96 raw pointer characters: only unmodified Left/Right reach fixed command-menu handlers; only exact Left, Shift-Left, and Middle reach its direct layout translators; all other states continue to generic presentation handlers or the dead-blip/beep path. Double Left is encoded as Shift-Left, simultaneous Left+Middle becomes Middle, and any simultaneous transition containing Right becomes Right. Active argument acquisition also changes precedence: its innermost pane-selection context can consume Left or Shift-Left before the outer idle Split translator.

Physical Shift-Right and unmodified Right double-click are the same raw character and are consumed by Essential Mouse before Dynamic Windows; Meta-Shift-Right remains the Window Operation Menu gesture. Click routing is also selection-sensitive: when the selected window accepts presentation blips, the clicked window supplies the object and coordinates but the selected window's active context and command table interpret them. Blank Left offers Select This Window only for a different window alias. A leaf's Right Operation menu contains the two Split forms, Set Pane Options, Set Pane Name, and Delete plus applicable generic styled submenus, including Marking and Yanking when its Input Editor context/menu tester applies; an internal node omits Split. Blank Right includes Window Operation and can also include System, Select This Window, and the Input Editor's Marking and Yanking submenu when their testers apply.

Nested interactions keep their own maps. Program and pane option forms use the full Accepting Values accelerator/pointer tree; Select/Reset confirmation is a readline Yes/No FQUERY with Input Editor and completion rather than a one-key Y/N prompt; Preview returns on an ordinary character but routes Refresh, intercepts, and pointer blips through the generic character-reader paths. These context changes are why the specification records a tree rather than a flat key list.

Pane types and editable options

The public Genera manual describes six Frame-Up pane types. The inspected Genera 8.5 source registry defines those six plus :TREE-BROWSER, and Frame-Up enumerates the registry dynamically. Loaded systems can therefore extend the set; the menu is not a fixed six-element constant.

The options form special-cases two interacting groups. Redisplay can be None, String, or Function; choosing one removes incompatible properties, and a function can enable incremental redisplay. Command menus can use defaults, a numeric row/column count, or explicit lists of item strings.

The source and manual disagree on one default. The manual describes inherited tables including standard scrolling; the inspected definition initializes Frame-Up's model with colon full command, standard arguments, and input editor compatibility. The source value is the claim made here for this Genera 8.5 artifact.

How the pane model works

Frame-Up stores a tree of layout-pane objects. Leaves are the panes that will appear in generated code. Internal nodes use private :ROW and :COLUMN types and must not escape into the emitted pane catalog.

Splitting a leaf follows two rules:

1. If the parent already has the desired orientation, add the new sibling directly after the selected pane.
2. Otherwise wrap the old leaf and its new sibling in a new hidden row or column, replacing the old leaf in its former parent.

The selected pane's stored direction participates in laying out inferiors and in promotion after deletion; the Split dispatcher does not read it to select a later split direction. Deletion performs the inverse cleanup by collapsing a hidden parent with one survivor. Swap is intentionally restricted to siblings so the operation never has to reconcile two different constraint contexts.

The built-in configuration named title display command-menu interactor actually constructs children in the order title, command menu, display, interactor. Its label is not a reliable serialization of child order.

What Frame-Up generates

The result is a DEFINE-PROGRAM-FRAMEWORK form containing:

• optional Select key;
• command-defining macro;
• inherited command-table names and accelerator policy;
• state variables;
• leaf pane descriptions with only allowed options; and
• one named configuration with layout and size constraints.

If any node is :ACCEPT-VALUES, generation automatically adds the accept-values-pane command table. A last-resort path emits a one-pane column and an even size when the default unsplit model would otherwise produce no layout description.

Done stores one latest definition per program name in memory. A direct Frame-Up session therefore does not write a file; Insert Program Definition is needed later from Zmacs. An editor-launched session waits for the result tick and inserts the form at point.

Complete Zmacs integration

Four named commands are installed in the standard Zmacs command table. Both M-X (Extended Command) and C-M-X (Any Extended Command) reach all four through name completion; the source assigns none a command-specific direct chord. The extended-command prompt uses Zmacs Mini-IE: its local completion, Help, yank, quote, abort, conditional Return, and explicitly undefined shadows sit above the full Standard Zwei map and C-X prefix tree. Pressing C-M-X inside an active M-X prompt converts it to Any Extended Command without discarding entered text.

The public Frame-Up chapter lists the first three commands; the fourth is a source-visible addition. Edit Program Definition is intentionally conservative: it warns that added options will be lost, edited values will revert, and deleted options will reappear, and asks before proceeding. This behavior follows from the fact that Frame-Up retains its last model rather than parsing arbitrary framework code back into a model.

Source-visible limitations omitted or understated by the manual

• The graphical display is a simulation of constraint-frame layout, not the normal layout engine. Its size functions estimate command-menu width from an average item width and scale character units internally, so it should not be read as a pixel-exact WYSIWYG renderer. All-fixed children are laid out at their computed sizes even beyond the parent, and negative unconstrained extents are not clipped. Preview is the authoritative visual check.
• A source comment identifies unique pane naming as buggy when a standard layout has more than one pane of a given type.
• The state-variable editor is commented out with a note that it does not work well. State variables can still appear in generated forms, but this source does not provide the intended interactive editor for them.
• The source contains a release-7 fallback for an unsplit one-pane configuration, described there as a last-minute fix rather than the preferred layout model.
• Split and Delete assume a coherent private pane tree. Splitting a stale/nonmember node can leave a sibling backlink before signaling, or build a detached linked subtree when orientations differ. Deleting a stale target can still promote an unrelated sole survivor, while zero or multiple survivors stop after destructive list replacement; old backlinks are not cleared.
• Editing an existing definition is model-based and lossy, as described above; it is not a general code-to-layout decompiler.
• Generating a form while an Accept Values pane exists permanently adds that pane's command table to the designer's stored inheritance list; deleting the pane later does not remove the entry.
• Preview evaluates/redefines the actual program name in the current world before displaying a temporary processless frame. Its prompt asks for Space, but any character returns. A later error does not roll back the definition.
• The Zmacs handoff uses one global result tick and later inserts the first retained result. A fast Done can precede the wait snapshot, multiple callers can wake together, and a nonfirst program can receive the wrong first result. Editing also deletes the old interval before inserting replacement text, so insertion failure can leave the definition absent.

System 303 Screen Editor

Runtime observation: the 15-item Screen Editor menu in LM-3 System 303, captured 2026-07-18 after selecting Edit Screen from the live System Menu. No geometry or window command was executed. MIT and other underlying software/display interests remain with their respective rightsholders; the image is reproduced for criticism, scholarship, and historical documentation under 17 U.S.C. section 107. No affiliation or endorsement is implied.

The captured ordering exactly matches the pinned System 303 source. The pointer landed on Reshape, and the who line displayed its operation-specific explanation, which also confirms that the maintained menu's documentation metadata is live UI. The menu was then exited without changing geometry.

Genera 8.5 Frame-Up

Runtime observation: Frame-Up in the licensed Genera 8.5 world after executing Split Pane PANE-1 Horizontally, captured 2026-07-18. The pane model and command transcript substantiate the source/manual analysis. Symbolics and other underlying software/display interests remain with their respective rightsholders; reproduced for criticism, scholarship, and historical documentation under 17 U.S.C. section 107. No affiliation or endorsement is implied.

Select Q opened Frame-Up directly with the documented dummy program and one display pane. Choosing Split Pane, pointing at the PANE-1 presentation, and completing Horizontally produced two equal panes stacked above and below a horizontal divider. The interactor retained the exact command. Choosing Done returned to the prior Dynamic Lisp Listener. This direct invocation changed only unsaved Lisp state; it did not insert source into a buffer or save the world.

The action prefix also preserves two unsuccessful exploratory inputs: a Left click in pane whitespace caused no visible layout change, and a Right click opened Genera's generic Operation menu rather than a Frame-Up pane menu. The operation menu was dismissed without a choice. No broader gesture inference is made from those attempts.

Genera 8.5 Screen Editor

Runtime observation: selecting Edit Screen from the live Genera 8.5 System Menu opened this inherited Screen Editor menu on 2026-07-18. No geometry command was selected. The capture is published to compare the actual menu with the MIT lineage beside substantive source analysis; Symbolics and other underlying interests remain with their rightsholders, and inclusion implies no endorsement.

The rendered menu has the same fifteen labels and grouping established by the licensed source: Bury, Expose, Expose (menu), Create, Create (expand), Kill, Exit, Undo, Move window, Reshape, Move multiple, Move single, Expand window, Expand all, and Attributes. The pointer was on Undo, and the bottom line confirmed the source-defined exception that Undo cannot reverse Create or Kill. The harness then selected Exit without applying a geometry operation and returned to the Listener. The prior synthetic debugger transcript visible behind the menu is session context, not an input to Screen Editor and contains no user data.