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Implement generators: GEN, EMIT, END GEN, FOR EACH and DO EACH (issue 57) 
Adds generator support per the plan in issue 57:

- environment.h: isGenerator/generatorFn on a GEN call's own environment,
  isEachLoop and forGeneratorEnv on a FOR EACH/DO EACH loop's own
  environment.
- runtime.c: splits akbasic_runtime_prev_environment() into
  akbasic_runtime_detach_environment() (return to parent without releasing)
  and akbasic_runtime_release_environment() (give variables and the pool
  slot back, on any environment); prev_environment() is now the two in
  sequence. akbasic_runtime_call_function() refuses to call a GEN like an
  ordinary function.
- verbs.c/verbs.h/scanner: new keywords GEN, EMIT, EACH, IN and the compound
  verb "END GEN" (built by a new akbasic_parse_end(), the same trick
  akbasic_parse_print() uses for PRINT #).
- parser_commands.c: akbasic_parse_gen() (modelled on multi-line DEF),
  akbasic_parse_end(), and EACH branches in akbasic_parse_for()/
  akbasic_parse_do().
- runtime_generator.c (new): akbasic_cmd_gen, akbasic_cmd_emit,
  akbasic_cmd_end_gen, and the invoke/pump/release machinery FOR EACH, DO
  EACH, NEXT and LOOP share. EMIT walks up to the nearest isGenerator
  ancestor rather than assuming it is standing directly in the GEN's own
  call frame, because a GEN body may nest its own FOR/DO/GOSUB around an
  EMIT -- the issue's own ROOMOBJECTS example does exactly that.
- runtime_commands.c/runtime_structure.c: EACH branches in cmd_for/cmd_do,
  matching EACH branches in cmd_next/cmd_loop, and forGeneratorEnv release
  on every path that can abandon a live generator (EXIT, a NEXT that pops
  for a mismatched loop variable).

Deviates from the plan in one place: FunctionDef gained an isGenerator flag
(not in the plan's field list) because refusing a GEN called like a
function has to happen before anything is pushed. Relying on EMIT's own
isGenerator check for that case doesn't work: akbasic_runtime_call_function()
drives its own step loop the same way akbasic_runtime_pump_generator() does,
and a BASIC-level error inside that loop is swallowed by process_line_run()
as reported-but-not-propagated, so the call would silently "succeed" with a
meaningless return value instead of failing.

Also: a zero-argument parameter list is not supported by the DEF/GEN
parameter parser this reuses (a pre-existing limitation, not
generator-specific); every generator in the tests takes at least one
parameter as a result.

Tests: tests/generators.c (pool exhaustion under repeated EXIT, calling a
GEN like a function, EMIT outside a GEN, self-recursion, sibling/nested
invocations) and tests/language/flowcontrol/generators_*.bas -- the
issue's own ROOMOBJECTS example in both loop shapes, an empty generator,
non-numeric EMIT, nested/interleaved invocations, and three error-path
golden cases. Docs: control-flow chapter 4 gets a GEN/EMIT/FOR EACH/DO EACH
section, the verb reference gets GEN/EMIT/END GEN entries and updated
FOR/DO/NEXT/LOOP/EXIT rows, and architecture chapter 14 documents the
detach/release split and the two-environment generator invocation.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
2026-08-06 10:02:43 -04:00

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# 11. Verb reference
Every statement, alphabetically. This list is generated from the interpreter's own
dispatch table, so it cannot drift out of step with what the program actually accepts.
A verb marked **Refused** parses and then reports why it cannot run — see Chapter 13
for the reasoning in each case.
| Verb | Form | What it does |
|---|---|---|
| `APPEND` | `APPEND n, "name"` | Open a file on channel `n` for writing at its end. |
| `AUTO` | `AUTO n` | Number lines automatically in steps of `n`. `AUTO 0` turns it off. |
| `BACKUP` | `BACKUP` | **Refused.** Duplicates one disk onto another; there are no disks. |
| `BEGIN` | `IF c THEN BEGIN` | Start a block that runs to `BEND`, so an `IF` can span lines. |
| `BEND` | `BEND` | End a `BEGIN` block. |
| `BLOAD` | `BLOAD "name", addr, len` | Read a file into memory. The length is required. |
| `BOOT` | `BOOT` | **Refused.** Loads and runs a boot sector; there is none. |
| `BOX` | `BOX src, x1, y1, x2, y2 [,angle]` | Outline a rectangle, optionally rotated. |
| `BSAVE` | `BSAVE "name", from, to` | Write a range of memory to a file. |
| `CATALOG` | `CATALOG` | **Refused.** The other name for `DIRECTORY`. |
| `CHAR` | `CHAR col, x, y, "text"` | Put text at a character cell. Needs a sink with a cursor. Terminates the row where it stops, so it erases whatever followed. |
| `CIRCLE` | `CIRCLE src, x, y, rx, ry [,...]` | Draw an ellipse, arc or polygon. |
| `CLR` | `CLR` | Drop every variable and function, keeping the program. |
| `COLLECT` | `COLLECT` | **Refused.** Validates a disk's block allocation map. |
| `COLLISION` | `COLLISION type [,target]` | Call a subroutine when sprites collide. No target disarms it. |
| `COLOR` | `COLOR src, index` | Bind a colour source to a palette index, 1 to 16. |
| `CONCAT` | `CONCAT "a", "b"` | Append file `a` to file `b`. |
| `CONT` | `CONT` | Resume a program stopped by `STOP`. |
| `COPY` | `COPY "a", "b"` | Copy file `a` to file `b`. |
| `DATA` | `DATA v [, ...]` | Declare values for `READ`. Collected before the program runs. |
| `DCLEAR` | `DCLEAR` | Close every open channel. The half of a drive reset that means something. |
| `DCLOSE` | `DCLOSE [n]` | Close channel `n`, or every channel. |
| `DEF` | `DEF NAME(args) = expr` | Define a function. Multi-line definitions end in `RETURN`. |
| `DELETE` | `DELETE [n][-n]` | Delete lines, with the same range forms as `LIST`. |
| `DIALOG` | `DIALOG ["text"]` | Show a text panel across the bottom of the screen. No argument takes it down. See Chapter 19. |
| `DIM` | `DIM A#(n [,...])` | Make an array. Subscripts start at zero; `n` is the count. |
| `DIM` … `AS` | `DIM S@ AS T`, `DIM P@ AS PTR TO T` | Make a structure, or a strict pointer to one. See Chapter 16. |
| `DIRECTORY` | `DIRECTORY` | **Refused.** Not written yet; the standard-library wrapper it waited on has landed. |
| `DLOAD` | `DLOAD "name"` | Load a program from a file. |
| `DO` | `DO [WHILE c | UNTIL c]`, `DO EACH V IN gen(args)` | Start a loop. The condition may be here, on the `LOOP`, or neither. `EACH` consumes a `GEN` instead; see Chapter 4. |
| `DOPEN` | `DOPEN n, "name" [,W]` | Open a file on channel `n`. `W` opens it for writing. |
| `DRAW` | `DRAW src, x, y [TO x, y ...]` | Plot a point or draw a polyline. |
| `DSAVE` | `DSAVE "name"` | Save the program to a file. |
| `DVERIFY` | `DVERIFY "name"` | The other name for `VERIFY`. |
| `EMIT` | `EMIT expr` | Yield one value from a `GEN` body. Only valid inside one; see Chapter 4. |
| `END` | `END` | Stop the program. Does not arm `CONT`. |
| `END GEN` | `END GEN` | Close a `GEN` body, the way `RETURN` closes a multi-line `DEF`. |
| `ENVELOPE` | `ENVELOPE n, a, d, s, r` | Define one of `PLAY`'s ten envelope presets. |
| `EXIT` | `EXIT` | Leave the innermost `FOR`, `FOR EACH`, `DO` or `DO EACH` loop. |
| `FETCH` | `FETCH count, from, to` | Copy bytes. The same as `STASH`; there is no expansion RAM. |
| `FILTER` | `FILTER ...` | **Refused.** There is no filter stage in the audio backend. |
| `FOR` | `FOR V = a TO b [STEP c]`, `FOR EACH V IN gen(args)` | Start a counted loop, ended by `NEXT`. `EACH` consumes a `GEN` instead; see Chapter 4. |
| `GEN` | `GEN NAME(args) ... END GEN` | Define a generator: a subroutine that yields more than once via `EMIT`, consumed by `FOR EACH`/`DO EACH`. See Chapter 4. |
| `GET` | `GET V` | Take a keystroke if one is waiting, without stopping. |
| `GETKEY` | `GETKEY V` | Wait for a keystroke, holding the program but not the host. |
| `GETMENU` | `GETMENU n, V%` | Wait for a menu choice, holding the program but not the host. Assigns the entry number. See Chapter 19. |
| `GOSUB` | `GOSUB line` | Call a subroutine, returning on `RETURN`. |
| `GOTO` | `GOTO line` | Jump to a line or a label. |
| `GRAPHIC` | `GRAPHIC mode | CLR` | Choose a screen mode, or clear it. |
| `GSHAPE` | `GSHAPE A$, x, y` | Stamp a region saved by `SSHAPE`. |
| `HEADER` | `HEADER "name"` | **Refused.** Formats a disk. |
| `HELP` | `HELP` | Re-list the line the last error happened on. |
| `HUD` | `HUD n [,anchor, "text"]` | Pin a line of text to a corner or the centre. No text retires the slot; no arguments retire them all. See Chapter 19. |
| `IF` | `IF c THEN s [ELSE s]` | Branch. Everything after `THEN` belongs to the condition. |
| `INPUT` | `INPUT ["prompt"] V` | Read a line from the user. |
| `INPUT#` | `INPUT #n, V` | Read a line from a channel. |
| `KEY` | `KEY [n, "text"]` | Define a function-key macro, or list them all. |
| `LABEL` | `LABEL NAME` | Mark this line with a name any branch can use. |
| `LET` | `LET V = expr` | Assign. Optional; assignment needs no verb. |
| `LIST` | `LIST [n][-n]` | List the program, or part of it. |
| `LOAD` | `LOAD "name"` | The other name for `DLOAD`. |
| `LOCATE` | `LOCATE x, y` | Move the pixel cursor. |
| `LOOP` | `LOOP [WHILE c | UNTIL c]` | End a `DO` loop, including a `DO EACH`. |
| `MENU` | `MENU [n [,"item", ...]]` | Show a menu the player picks from. No entries retires it; no arguments retire them all. See Chapter 19. |
| `MOVSPR` | `MOVSPR n, ...` | Move a sprite. Four forms; see Chapter 8. |
| `NEW` | `NEW` | Erase the program and every variable. |
| `NEXT` | `NEXT V` | End a `FOR` loop and advance its counter, or resume a `FOR EACH` for its next value. |
| `ON` | `ON e GOTO|GOSUB t [,...]` | Branch to the `e`th target, counting from one. |
| `PAINT` | `PAINT src, x, y` | Flood-fill the region containing a point. |
| `PLAY` | `PLAY "notes"` | Queue notes. Does not block. |
| `POINT` | `POINT P@ AT s@` | Aim a strict pointer at a structure. See Chapter 16. |
| `POKE` | `POKE addr, byte` | Write a byte to a real address. |
| `PRINT` | `PRINT [expr]` | Print a value and a newline. |
| `PRINT#` | `PRINT #n, expr` | Write a line to a channel. |
| `PUDEF` | `PUDEF "chars"` | Redefine what `PRINT USING` pads and punctuates with. |
| `QUIT` | `QUIT` | End the interpreter. |
| `READ` | `READ V [,...]` | Fill variables from the next `DATA` items. |
| `RECORD` | `RECORD n, r [,pos]` | Position a channel at record `r`. Records are lines. |
| `RENAME` | `RENAME "a", "b"` | Rename a file. |
| `RENUMBER` | `RENUMBER [start [,step [,from]]]` | Renumber lines, rewriting every branch to match. |
| `RESTORE` | `RESTORE [line]` | Reset the `READ` cursor, optionally to a line. |
| `RESUME` | `RESUME [NEXT | line]` | Return from a `TRAP` handler. |
| `RETURN` | `RETURN [expr]` | Return from a `GOSUB` or a multi-line `DEF`. |
| `RUN` | `RUN [line]` | Run the program, optionally from a line. |
| `SAVE` | `SAVE "name"` | The other name for `DSAVE`. |
| `SCALE` | `SCALE on [,xmax, ymax]` | Turn user coordinates on or off. |
| `SCNCLR` | `SCNCLR` | Clear the text screen. |
| `SCRATCH` | `SCRATCH "name"` | Delete a file. |
| `SLEEP` | `SLEEP seconds` | Pause. Holds the program, not the host. |
| `SOLID` | `SOLID [id [,x1, y1, x2, y2]]` | Register static collision geometry a sprite can hit. No rectangle retires it; no arguments retires them all. See Chapter 8. |
| `SOUND` | `SOUND v, freq, dur [,...]` | Play a tone on a voice. Does not block. |
| `SPRCOLOR` | `SPRCOLOR [c1] [,c2]` | Set the two shared multicolour registers. |
| `SPRHIT` | `SPRHIT n, kind [,x1, y1, x2, y2]` | Give a sprite a collision shape. Kind 0 none, 1 box, 2 circle, 3 or 4 capsule. No rectangle fits the frame. See Chapter 8. |
| `SPRITE` | `SPRITE n [,on] [,col] [,...]` | Configure a sprite. Omitted arguments are left alone. |
| `SPRSAV` | `SPRSAV source, n` | Give sprite `n` a picture. Three source forms; see Chapter 8. |
| `SSHAPE` | `SSHAPE A$, x1, y1 [,x2, y2]` | Save a screen region; `A$` receives a handle. |
| `STASH` | `STASH count, from, to` | Copy bytes. The same as `FETCH`. |
| `STOP` | `STOP` | Stop the program; `CONT` resumes it. |
| `SWAP` | `SWAP A, B` | Exchange two variables of the same type. |
| `SYS` | `SYS addr` | **Refused.** There is no 6502 and no ROM to call. |
| `TEMPO` | `TEMPO n` | How fast `PLAY` releases its queue. |
| `TRAP` | `TRAP [target]` | Send errors to a handler. No target disarms it. |
| `TROFF` | `TROFF` | Turn line tracing off. |
| `TRON` | `TRON` | Turn line tracing on; each line prints its number in brackets. |
| `TYPE` | `TYPE NAME` … `END TYPE` | Declare a record, its fields one per line. See Chapter 16. |
| `UISTYLE` | `UISTYLE [fill, edge, ink [,pad [,radius]]]` | The one look every widget draws with. No arguments restores the default. See Chapter 19. |
| `VERIFY` | `VERIFY "name"` | Compare the program in memory against a file. |
| `VOL` | `VOL n` | Set the overall volume, 0 to 15. |
| `WAIT` | `WAIT addr, mask [,xor]` | Poll a byte until it matches. Holds the program. |
| `WIDTH` | `WIDTH 1|2` | How thick a drawn line is. |
| `WINDOW` | `WINDOW l, t, r, b [,clear]` | Constrain the text area. Needs a sink with a grid. |
## Words that are not verbs
`AND`, `ELSE`, `NOT`, `OR`, `REM`, `STEP`, `THEN`, `TO`, `UNTIL`, `USING` and `WHILE`
are reserved, but none of them is a statement on its own — each is consumed by the verb
it belongs to.
## Deliberately absent
`BANK`, `FAST`, `MONITOR` and `SPRDEF` have no table entry at all. The first three are
incompatible with a modern machine — there is no bank switching, no CPU speed to
control, and no machine-language monitor to drop into. `SPRDEF` is an interactive
full-screen editor rather than a programmable verb.
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