Peek on the MIT Lisp Machine

Evidence sets

Purpose and entry points

Peek can be reached through:

• System P, which selects or creates a Peek frame;
• Peek in the System 303 System Menu's Programs column;
• Create, then Peek, in the System Menu;
• the Lisp function (PEEK), optionally with an initial mode.

System 46 has a process-bearing PEEK window with no mode menu. One is pre-created for the System key, and its standalone top level initially invokes Help. The System 46 function (PEEK) is a different entry: it temporarily binds a BASIC-PEEK display over a supplied terminal window and defaults to Active Processes.

The System 303 source distinguishes two later window forms. PEEK-FRAME combines a mode menu with the display pane. PEEK-WINDOW is a standalone process-bearing display without that menu; it is controlled entirely by keyboard commands. A standalone instance initially invokes Help before entering the normal update loop.

The function (PEEK initial-mode) selects or creates a frame and injects the first character of a string or symbol argument, or the supplied character, into its input stream. The requested mode is therefore selected through the same command loop as user input rather than by a separate private API.

Update model

Normal modes produce scrolling display items whose dynamic fields are reevaluated on redisplay. The default interval is 120 sixtieths of a second, or two seconds. Each mode can combine:

• fixed text and headings;
• functions that recompute displayed values;
• maintained lists whose members can appear and disappear;
• nested rows inserted or removed by clicking a parent item;
• mouse-sensitive values that open an object-specific menu.

System 303's wait loop treats exposure explicitly. While Peek is deexposed it notices that an update deadline has passed without drawing into the hidden window. When the window becomes exposed again, it resumes redisplay instead of waiting indefinitely for a deadline that expired while hidden.

Some modes are one-shot operations rather than continuously updated displays. Selecting one lets it write into the typeout window, then restores the prior mode's label and highlighted menu item after the temporary output is dismissed.

If typeout is still present when Peek needs to resume, it prompts for any character. Space dismisses the typeout and is consumed. Any other character is put back into the input stream and handled as a Peek command. This small detail prevents the acknowledgment from swallowing a requested mode switch.

Keyboard command inventory

System 46 mode inventory

The pinned System 46 peek.75 defines eight modes:

The System 46 application has no mode-menu pane: the source starts in ? Help and expects these characters. The contemporary manual lists the broad subsystems but calls the individual displays self-explanatory; the source is needed for the action menus and nested interactions below.

System 303 mode inventory

System 303 makes the mode registry extensible. DEFINE-PEEK-MODE adds or replaces a character entry at load time and rebuilds the command menu from the effective list. Help reads that same registry. The list can therefore vary with loaded subsystems.

The pinned core and Chaosnet files, and the fresh loaded System 303-0 band, provide these twelve modes:

The mode menu uses the compact display font rather than the window system's usual larger menu font. It highlights the active mode, and refreshes its item list if modes were added while the frame was deexposed.

Context-menu inventory

Findings not evident from the manual's overview

• Peek's mode set is a load-time registry in System 303, so Help and the mode menu describe the effective loaded system rather than an immutable manual table.
• The n Z interval changed units: raw sixtieths in System 46, seconds in System 303.
• Hidden Peek windows track missed deadlines and deliberately redisplay after reexposure.
• One-shot modes restore the prior label and menu highlight after typeout.
• A non-Space typeout acknowledgment is put back and interpreted as a command.
• Areas can expand into live region and garbage-collector state; it is not merely an aggregate memory chart.
• General Status records have setter functions, but the displayed row spec does not expose an edit operation. Internal representation is not being promoted into a claimed UI feature.
• Later process, window, file, host, and connection menus add inspection and description paths and, for several dangerous operations, confirmation. Other dangerous operations remain immediate.

Runtime observation: System 303-0

A fresh Xvfb computer-use session selected Peek with System P. The initial Help view visibly listed all twelve modes above, followed by Q, nZ, and Help. Selecting P produced the Active Processes table with the source-defined columns and clock-function section. Clicking the first process opened the eight-item process menu; it was dismissed without selecting an action.

The relevant ordered input was System P, Space and P to select or refresh Active Processes, left click on the first process row to open its action menu, then a click outside the menu to dismiss it. No action-menu command was chosen.

Three raw 768×963 captures remain in the ignored session:

The image-by-image review selected only the non-menu Active Processes state for the curated CADR screenshot catalog. The Help and process-action-menu captures remain ignored: the former contains more explanatory text than this claim needs, and the latter is unnecessary to show the monitoring table.

Runtime observation: Peek's Active Processes mode in LM-3 System 303, captured 2026-07-18. Underlying software and display material remain the property of their respective rightsholders; reproduced here for criticism, scholarship, and historical documentation under 17 U.S.C. section 107. No affiliation or endorsement is implied.

The 6,781-byte run record has SHA-256 2d877843f58a8a261bafe68afca846919963dec5584a39bbb5275fcbe6615e22. Shutdown was clean: forced_stop and state_may_be_incomplete are false, the emulator and Xvfb both exited zero, and the base disk was unchanged. The computer-use harness article explains the evidence schema and repeat procedure.

Limits and open questions

• Only Help, Active Processes, and the process-menu surface were exercised in the runtime pass. The other mode descriptions and menus are source-grounded, not individually runtime-confirmed.
• No destructive command was selected. Confirmation behavior is established from source and remains to be exercised only against disposable objects.
• No runnable System 46 band was used. Its behavior here is source- and manual-grounded only.
• The twelve-mode list is complete for the pinned core/Chaos files and observed band, but the registry design allows another configured band to add modes.
• The exact history of when individual modes and confirmation prompts entered the code line has not been established.
• The Active Processes capture received a separate per-image publication review; the Help and action-menu captures remain ignored and unreviewed for publication.

Sources

Source links and pinned revisions last verified 2026-07-18.

• MIT CADR System 46, PEEK.75, Peek implementation.
• MIT CADR System 46, OPERAT.27, window-system operations manual source.
• LM-3 System 303, window/peek.lisp, maintained Peek framework and local modes.
• LM-3 System 303, network/chaos/peekch.lisp, Chaosnet modes and interactions.
• Local System 303-0 Xvfb observation, session core-env-20260718, generation 1, 2026-07-18; raw evidence identified above.