Abstract
========
-The Muddle programming language began existence in late 1970 (under
-the name Muddle) as a successor to Lisp (Moon, 1974), a candidate
-vehicle for the Dynamic Modeling System, and a possible base for
-implementation of Planner (Hewitt, 1969). The original design goals
-included an interactive integrated environment for programming,
-debugging, loading, and editing: ease in learning and use; facilities
-for structured, modular, shared programs; extensibility of syntax,
-data types and operators: data-type checking for debugging and
-optional data-type declarations for compiled efficiency; associative
-storage, coroutining, and graphics. Along the way to reaching those
-goals, it developed flexible input/output (including the ARPA
-Network), and flexible interrupt and signal handling. It now serves as
-a base for software prototyping, research, development, education, and
-implementation of the majority of programs at MIT-DMS: a library of
-sharable modules, a coherent user interface, special research
+The Muddle programming language began existence in late 1970 as a
+successor to Lisp (Moon, 1974), a candidate vehicle for the Dynamic
+Modeling System, and a possible base for implementation of Planner
+(Hewitt, 1969). The original design goals included an interactive
+integrated environment for programming, debugging, loading, and
+editing: ease in learning and use; facilities for structured,
+modular, shared programs; extensibility of syntax, data types and
+operators: data-type checking for debugging and optional data-type
+declarations for compiled efficiency; associative storage,
+coroutining, and graphics. Along the way to reaching those goals, it
+developed flexible input/output (including the ARPA Network), and
+flexible interrupt and signal handling. It now serves as a base for
+software prototyping, research, development, education, and
+implementation of the majority of programs at MIT-DMS: a library of
+sharable modules, a coherent user interface, special research
projects, autonomous daemons, etc.
This document was originally intended to be a simple low-level
I was not a member of the original group which labored for two years
in the design and initial implementation of Muddle; that group was
-composed principally of Gerald Sussman, Carl Hewit, Chris Reeve, Dave
+composed principally of Gerald Sussman, Carl Hewitt, Chris Reeve, Dave
Cressey, and later Bruce Daniels. I would therefore like to take this
opportunity to thank my Muddle mentors, chiefly Chris Reeve and Bruce
Daniels, for remaining civil through several months of verbal
There are no "practice problems"; you are assumed to be learning
Muddle for some purpose, and your work in achieving that purpose will
-be more useful and motivated than artificial problems. In several
+be more useful and motivating than artificial problems. In several
cases, the examples contain illustrations of important points which
-are not covered in the text. Ignore examples as your peril.
+are not covered in the text. Ignore examples at your peril.
This document does not assume knowledge of any specific programming
language on your part. However, "computational literacy" is assumed:
`ROOT`. A metasyntactic variable -- something to be replaced in actual
use by something else -- appears as *radix:fix*, in an italic font;
often the variable will have both a meaning and a data type (as here),
-but sometimes one of those will be ommitted, for obvious reasons.
+but sometimes one of those will be omitted, for obvious reasons.
An ellipsis (...) indicates that something uninteresting has been
omitted. The character `^` means that the following character is to be
-------------------------
First, catch your rabbit. Somehow get the interpreter running -- the
-program in the file `SYS:TS.Muddle` in the ITS version or
-`SYS:Muddle.SAV` in the Tenex version or `SYS:Muddle.EXE` in the
+program in the file `SYS:TS MDL` in the ITS version or
+`SYS:MDL.SAV` in the Tenex version or `SYS:MDL.EXE` in the
Tops-20 version. The interpreter will first type out some news
relating to Muddle, if any, then type
done, the result will be printed and Muddle will wait for more typing.
`ESC` will be represented by the glyph `$` in this document.
-Typing the rubout character (`DEL` in the ITS and Top-20 versions,
+Typing the rubout character (`DEL` in the ITS and Tops-20 versions,
`CTRL`+`A` in the Tenex version) causes the last character in the
buffer -- the one most recently typed -- to be thrown away (deleted).
If you now immediately type another rubout, once again the last
IMLAC, ARDS, Datapoint), it firsts clears the screen.
Typing `^G` (`CTRL`+`G`) causes Muddle to stop whatever it is doing
-and act as if an error had occurred ([section
-1.4](#14-errors-simple-considerations-1)). `^G` is generally most
-useful for temporary interruptions to check the progress of a
+and act as if an error had occurred (section 1.4). `^G` is generally
+most useful for temporary interruptions to check the progress of a
computation. `^G` is "reversible" -- that is, it does not destroy any
of the "state" of the computation it interrupts. To "undo" a `^G`,
type the characters
(This is discussed more fully far below, in section 16.4.)
Typing `^S` (`CTRL`+`S`) causes Muddle to **throw away** what it is
-currently doing and return a normal "listening" state. (In the Tenex
-and Tops-20 versions, `^O` also should have the same effect.) `^S` is
-generally most useful for aborting infinite loops and similar terrible
-things. `^S` **destroys** whatever is going on, and so it is **not**
-reversible.
+currently doing and return to a normal "listening" state. (In the
+Tenex and Tops-20 versions, `^O` also should have the same effect.)
+`^S` is generally most useful for aborting infinite loops and similar
+terrible things. `^S` **destroys** whatever is going on, and so it is
+**not** reversible.
Most expressions in Muddle include "brackets" (generically meant) that
must be correctly paired and nested. If you end your typing with the
One way to "name" a `FUNCTION` is
<SETG SQUARE #FUNCTION ((X) <* .X .X>)>$
- #FUNCTION ((X) <* .X .X>
+ #FUNCTION ((X) <* .X .X>)
So that
Another way, which is somewhat cleaner in its typing:
<SETG SQUARE <FUNCTION (X) <* .X .X>>>$
- #FUNCTION ((X) <* .X .X>
+ #FUNCTION ((X) <* .X .X>)
`FUNCTION` is an `FSUBR` which simply makes a `FUNCTION` out of its
arguments and returns the created `FUNCTION`.
effect (in the absence of errors), and the intention is more apparent.
\[Note: if `.L` is a `LIST`, `<LIST !.L>` makes a copy of `.L` whereas
`(!.L)` doesn't; see section 7.7.\] `STRING`, on the other hand,
-produces effect very different from literal `STRING`s.
+produces effects very different from literal `STRING`s.
Examples:
The following table tells which `SUBR`s can be used with which modes,
where `OK` indicates an allowed use:
- -------------------------------------------------------------------------------------------------------------------------------------------------
- "READ" "PRINT" "READB" "PRINTB", "PRINTO" mode / SUBRs
- -------------------- --------------------- --------------------- -------------------------------------------- -----------------------------------
- OK OK `READ` `READCHR` `NEXTCHR`
- `READSTRING` `FILECOPY`
- `FILE-LENGTH LOAD`
+ -------------------------------------------------------------------------
+ "READ" "PRINT" "READB" "PRINTB", "PRINTO" mode / SUBRs
+ ------ ------- ------- ------------------ ------------
+ OK OK `READ` `READCHR` `NEXTCHR`
+ `READSTRING` `FILECOPY`
+ `FILE-LENGTH LOAD`
- OK OK\* `PRINT` `PRIN1` `PRINC` `IMAGE`
- `CRLF` `TERPRI` `FILECOPY`
- `PRINTSTRING` `BUFOUT` `NETS`
- `RENAME`
+ OK OK\* `PRINT` `PRIN1` `PRINC` `IMAGE`
+ `CRLF` `TERPRI` `FILECOPY`
+ `PRINTSTRING` `BUFOUT` `NETS`
+ `RENAME`
- OK `READB` `GC-READ`
+ OK `READB` `GC-READ`
- OK `PRINTB` `GC-DUMP`
+ OK `PRINTB` `GC-DUMP`
- OK OK OK `ACCESS`
+ OK OK OK `ACCESS`
- OK OK OK OK `RESET`
+ OK OK OK OK `RESET`
- OK OK `ECHOPAIR`
+ OK OK `ECHOPAIR`
- OK `TTYECHO` `TYI`
- -------------------------------------------------------------------------------------------------------------------------------------------------
+ OK `TTYECHO` `TYI`
+ -------------------------------------------------------------------------
`*` PRINTing (or `PRIN1`ing) an `RSUBR` (chapter 19) on a `"PRINTB"`
or `"PRINTO"` `CHANNEL` has special effects.
*element-number: type interpretation*
- ----------------------------------------------------------------------------------------------------
- element-number type interpretation
- -------------------------- ------------------ ------------------------------------------------------
- -1 `LIST` transcript channel(s) (see below)
+ -------------------------------------------------------------------------------------
+ element-number type interpretation
+ ---------------- ------------- ------------------------------------------------------
+ -1 `LIST` transcript channel(s) (see below)
- \* 0 varies device-dependent information
+ \* 0 varies device-dependent information
- \* 1 `FIX` channel number (ITS) or JFN (Tenex and Tops-20), `0`
- for internal or closed
+ \* 1 `FIX` channel number (ITS) or JFN (Tenex and Tops-20), `0`
+ for internal or closed
- \* 2 `STRING` mode
+ \* 2 `STRING` mode
- \* 3 `STRING` first file name argument
+ \* 3 `STRING` first file name argument
- \* 4 `STRING` second file name argument
+ \* 4 `STRING` second file name argument
- \* 5 `STRING` device name argument
+ \* 5 `STRING` device name argument
- \* 6 `STRING` directory name argument
+ \* 6 `STRING` directory name argument
- \* 7 `STRING` real first file name
+ \* 7 `STRING` real first file name
- \* 8 `STRING` real second file name
+ \* 8 `STRING` real second file name
- \* 9 `STRING` real device name
+ \* 9 `STRING` real device name
- \* 10 `STRING` real directory name
+ \* 10 `STRING` real directory name
- \* 11 `FIX` various status bits
+ \* 11 `FIX` various status bits
- \* 12 `FIX` PDP-10 instruction used to do one I/O operation
+ \* 12 `FIX` PDP-10 instruction used to do one I/O operation
- 13 `FIX` number of characters per line of output
+ 13 `FIX` number of characters per line of output
- 14 `FIX` current character position on a line
+ 14 `FIX` current character position on a line
- 15 `FIX` number of lines per page
+ 15 `FIX` number of lines per page
- 16 `FIX` current line number on a page
+ 16 `FIX` current line number on a page
- 17 `FIX` access pointer for file-oriented devices
+ 17 `FIX` access pointer for file-oriented devices
- 18 `FIX` radix for `FIX` conversion
+ 18 `FIX` radix for `FIX` conversion
- 19 `FIX` sink for an internal `CHANNEL`
- ----------------------------------------------------------------------------------------------------
+ 19 `FIX` sink for an internal `CHANNEL`
+ -------------------------------------------------------------------------------------
N.B.: The elements of a `CHANNEL` below number 1 are usually invisible
but are obtainable via `<NTH <TOP channel> fix>`, for some appropriate
respect to typing in carriage-return, in that it automatically adds a
line-feed. In order to type in a lone carriage-return, a
carriage-return followed by a rubout must be typed. Also `PRINT`,
-`PRINT1` and `PRINC` do not automatically add a line-feed when a
+`PRIN1` and `PRINC` do not automatically add a line-feed when a
carriage-return is output. This enables overstriking on a terminal
that lacks backspacing capability. It also means that what goes on a
terminal and what goes in a file are more likely to look the same.
produces objects of `TYPE` `LOCR` instead of `LOCD`.
19.5. TYPE-C and TYPE-W
-=======================
+-----------------------
In order to handle user `NEWTYPE`s reasonably, the internal `TYPE`
codes for them have to be able to be different from one Muddle run to
`FIX` which determines which interrupts can really "interrupt" -- that
is, cause the current processing to be suspended while their wants are
satisfied. Normal, non-interrupt programs operate at an interrupt
-level of 0 (zero.) An interrupt is processed at an interrupt level
+level of 0 (zero). An interrupt is processed at an interrupt level
equal to the interrupt's priority.
### 21.7.1. Interrupt Processing
priority than the target priority have been processed.
Setting the `INT-LEVEL` extremely high (for example,
-`<INT-LEVEL <CHTPE <MIN> FIX>>`) effectively disables all interrupts
+`<INT-LEVEL <CHTYPE <MIN> FIX>>`) effectively disables all interrupts
(but occurrences of enabled interrupts will still be queued).
If `LISTEN` or `ERROR` is called when the `INT-LEVEL` is not zero,
then the typeout will be
- LISTENING-AT-LEVEL I PROCESS p INT-LEVEL i
+ LISTENING-AT-LEVEL l PROCESS p INT-LEVEL i
### 21.7.3. DISMISS
interrupt, and the mode of the `CHANNEL` tells what kinds of `"CHAR"`
interrupts occur to be handled through that `IHEADER`.
-1. If the `CHANNEL` is for `INPUT`, "CHAR" occurs every time an
+1. If the `CHANNEL` is for `INPUT`, `"CHAR"` occurs every time an
"interesting" character (see below) is received from the
`CHANNEL`'s real terminal, or any character is received from the
`CHANNEL`'s pseudo-terminal, or a character or word is received
In the ITS version, the "interesting" characters are those "enabled
for interrupts" on a real terminal, namely `^@` through `^G`, `^K`
through `^_`, and `DEL` (that is, ASCII codes 0-7, 13-37, and 177
-octal.)
+octal).
In the Tenex and Tops-20 versions, the operating system can be told
which characters typed on a terminal should cause this interrupt to
friends). An interrupt occurs when a character is available for input.
These interrupts are set up in exactly the same way as real-terminal
interrupts, except that a handler gets applied to only **one**
-argument, the `CHANNEL`. Pseudo-terminal are not available in the
+argument, the `CHANNEL`. Pseudo-terminals are not available in the
Tenex and Tops-20 versions.
For any other flavor of ITS channel interrupt, a handler gets applied
a deferrable garbage collection that is needed because of exhausted
movable garbage-collected storage. Enabling this interrupt is the only
way a program can know that a garbage collection is about to occur. A
-handler takes two arguments: A `FIX` telling the number of machine
+handler takes two arguments: a `FIX` telling the number of machine
words needed and an `ATOM` telling what initiated the garbage
collection (see above). If it wishes, a handler can try to prevent a
garbage collection by calling `BLOAT` with the `FIX` argument. If the
### 21.8.6. "CLOCK"
`"CLOCK"`, when enabled, occurs every half second (the ITS
-"slow-clock" tick.) It is not available in the Tenex or Tops-20
+"slow-clock" tick). It is not available in the Tenex or Tops-20
versions. It wants handlers which take no arguments. Example:
<ON "CLOCK" <FUNCTION () <PRINC "TICK ">> 1>
### 21.8.8. "UNBLOCKED"
`"UNBLOCKED"` occurs whenever a `$` (`ESC`) is typed on a terminal if
-a program was hanging and waiting for input, or when a TYI call (which
-see) is satisfied. A handler takes one argument: the `CHANNEL` via
-which the `$` or character is input.
+a program was hanging and waiting for input, or when a `TYI` call
+(which see) is satisfied. A handler takes one argument: the `CHANNEL`
+via which the `$` or character is input.
### 21.8.9. "READ" and "WRITE"
handler takes one argument: A `FIX` between `0` and `7` inclusive,
telling which inferior process is interrupting.
-### 21.8.14. "RUNT and "REALT"
+### 21.8.14. "RUNT" and "REALT"
These are not available in the Tenex and Tops-20 versions.
`"MPV"` ("memory protection violation") occurs if Muddle tries to
refer to a storage address not in its address space. `"PURE"` occurs
if Muddle tries to alter read-only storage. `"ILOPR"` occurs if Muddle
-executes and illegal instruction ("operator"). `"PARITY"` occurs if
+executes an illegal instruction ("operator"). `"PARITY"` occurs if
the CPU detects a parity error in Muddle's address space. All of these
require a handler that takes one argument: the address (`TYPE` `WORD`)
following the instruction that was being executed at the time.
interrupt goes to the superior operating system process.
- If an `IHEADER` is associated but disabled, the error
`DANGEROUS-INTERRUPT-NOT-HANDLED` occurs (`FILE-SYSTEM-ERROR` for
- \`"IOC").
+ `"IOC"`).
- If an `IHEADER` is associated and enabled, but the `INT-LEVEL` is
too high, the error `ATTEMPT-TO-DEFER-UNDEFERABLE-INTERRUPT`
occurs.
Most storage used explicitly by Muddle programs is obtained from a
pool of free storage managed by a "garbage collector". Storage is
-obtained from this pool by the `SUBR`s which construct objects. When a
-`SUBR` finds that the pool of available storage is exhausted, it
-automatically calls the garbage collector.
+obtained from this pool by the `SUBR`s which construct objects. When
+such a `SUBR` finds that the pool of available storage is exhausted,
+it automatically calls the garbage collector.
The garbage collector has two algorithms available to it: the
"copying" algorithm, which is used by default, and the "mark-sweep"
lose.
Thus, if you just "forget about" an object, that is, lose all possible
-means of referencing it, its storage is automatically reclaimed.
+means of referencing it, its storage area is automatically reclaimed.
"Object" in this context includes that stack-structured storage space
used in `PROCESS`es for functional application.
5. Finally, the "mark-sweep" algorithm sweeps through the storage
space, adding unmarked objects to the internal free lists for
later re-use. The "copying" algorithm maps the inferior process's
- address space into Muddle's own, replacing old garbagey with the
- new compact storage, and the inferior process is destroyed.
+ address space into Muddle's own, replacing old garbagey storage
+ with the new compact storage, and the inferior process is
+ destroyed.
22.5 GC
-------
causes the garbage collector to run and returns the total number of
words of storage reclaimed. All of its arguments are optional: if they
-are not supplied, a call to GC simply causes a "copying" garbage
+are not supplied, a call to `GC` simply causes a "copying" garbage
collection.
If *min* is explicitly supplied as an argument, a garbage-collection
parameter is changed permanently before the garbage collector runs.
*min* is the smallest number of words of "free" (unclaimed, available
for use) movable garbage-collected storage the garbage collector will
-be satisfied with having after it is done. Initially it is 8192 words.
-If the total amount of reclaimed storage is less than *min*, the
-garbage collector will ask the operating system for enough storage (in
-1024 word blocks) to make it up. N.B.: the system may be incivil
-enough not to grant the request; in that case, the garbage collector
-will be content with what it has, **unless** that is not enough to
-satisfy a **pending** request for storage. Then it will inform you
-that it is losing. A large *min* will result in fewer total garbage
-collections, but they will take longer since the total quantity of
-storage to be dealt with will generally be larger. Smaller *min*s
-result in shorter, more frequent garbage collections.
+be satisfied with having after it is done each time. Initially it is
+8192 words. If the total amount of reclaimed storage is less than
+*min*, the garbage collector will ask the operating system for enough
+storage (in 1024-word blocks) to make it up. N.B.: the system may be
+incivil enough not to grant the request; in that case, the garbage
+collector will be content with what it has, **unless** that is not
+enough to satisfy a **pending** request for storage. Then it will
+inform you that it is losing. A large *min* will result in fewer total
+garbage collections, but they will take longer since the total
+quantity of storage to be dealt with will generally be larger. Smaller
+*min*s result in shorter, more frequent garbage collections.
+
+*exh?* tells whether or not this garbage collection should be
+"exhaustive". It is optional, a `FALSE` by default. The difference
+between normal and exhaustive "copying" garbage collections is whether
+certain kinds of storage that require complicated treatment (for
+example, associations) are reclaimed. An exhaustive garbage collection
+occurs every eighth time that the "copying" algorithm is used, or when
+`GC` is called with this argument true, or when a normal garbage
+collection cannot satisfy the storage request.
+
+*ms-freq* gives the number of times the "mark-sweep" algorithm should
+be used hereafter for every time the normal "copying" algorithm is
+used. Giving `0` for *ms-freq* means never to use the "mark-sweep"
+algorithm, and giving `<CHTYPE <MIN> FIX>` means (effectively) always
+to use it. The "mark-sweep" algorithm uses considerably less processor
+time than the "copying" algorithm, but it never shrinks the
+free-storage pool, and in fact the pool can become fragmented. The
+"mark-sweep" algorithm could be useful in a program system (such as
+the compiler) where the size of the pool rarely changes, but objects
+are created and thrown away continuously.
22.6. BLOAT
-----------
`READ`ing large `STRING`s, and calling routines within the
interpreter and compiled programs)
-Arguments on the second line are also `FIX` and optional, but they set
-garbage-collection parameters permanently, as follows:
+Arguments on the second line above are also `FIX` and optional, but
+they set garbage-collection parameters permanently, as follows:
- *min*: as for `GC`
- *plcl*: number of slots for `LVAL`s added when the space for
22.8. GC-MON
------------
- <GC-MOND pred>
+ <GC-MON pred>
("garbage-collector monitor") determines whether or not the
interpreter will hereafter print information on the terminal when a
Two `SUBR`s, described next, use only part of the garbage-collector
algorithm, in order to find all pointers to an object. `GC-DUMP` and
`GC-READ`, as their names imply, also use part in order to translate
-between Muddle objects and binary representation thereof.
+between Muddle objects and binary representations thereof.
### 22.9.1. SUBSTITUTE
the "wrong" one, after `OBLIST`s have been in the wrong state. This is
more or less the way `ATOM`s are impurified. It is also useful for
unlinking `RSUBR`s. `SUBSTITUTE` returns *old* as a favor: unless you
-hang onto *old* at that point, it will be garbage-collected.
+hang onto *old* at that point, it will be garbage.
22.9.2 PURIFY
-------------
("value return") seldom returns. It passes control back up the process
tree to the superior of Muddle, passing its argument as a message to
that superior. If it does return, the value is `#FALSE ()`. If the
-argument is a `STRING`, it is passed to the superior as a command to
+argument is a `STRING`, it is passed to the superior as commands to
be executed, via `.VALUE` in the ITS version and `RSCAN` in the
Tops-20 version. If the argument is a `FIX`, it is passed to the
-superior as the "effective address" of a `.BREAK 16`, instruction in
+superior as the "effective address" of a `.BREAK 16,` instruction in
the ITS version and ignored in other versions.
23.4. Inter-process Communication
projects / mudman.git / blobdiff