Add a mechanism to Forth that allows code sections/chapters to be loaded from a large 'file' with a simple command. How the file is stored and what it contains is implementation-dependent. What matters is the interface. The sections or chapters are accessible through one or more keywords.

The interface consists of the following word: NEED

• NEED ( "name" -- i*x ) Make sure “name” is present in the dictionary. If not, load it from a library. If “name” already exists, do nothing.

An optional word as suggested by Ulrich Hoffmann

• FROM ( "name" -- i*x ) Open the library “name” for use with NEED

Optional words as suggested by Willem Ouwerkerk

• NEEDED ( a b -- i*x ) Make sure that name represented by the string a b is present in the dictionary. If not, load it from a library. If name already exists, do nothing.
• .LIB ( -- ) Show all section/chapter headers of the current library in one or more columns

Function: NEEDED   ( a +n -- i*x )  \ a +n is keyword
    a) Check if the word represented by the string a +n exists in 
       the current search order.
    b) Do nothing the string was found, otherwise start searching 
       the active library for a keyword that matches this string.
    c) When the keyword is found load the source code chapter
       otherwise issue an error message
    
Function: NEED     ( "name" -- i*x )
    Perform the function of NEEDED using the parsed "name".
    
Function: .LIB     ( -- )
    Print all chapter headers in a human readable form.
    
Function: FROM     ( "name" -- )
    Make the library "name" the current active library
    When "name" was not found issue an error message

Implementations

Here, I will elaborate on an example that stores the source in Flash memory. For this implementation, there are the following design requirements:

- Simple structure ( idea A.N. )
- Quick search function
- Extensible: OPEN-LIB CHAPTER CLOSE-LIB WIPE-LIB
- Easy to use: NEED etc.

This library mechanism is based on two control characters 09 and 0D. They act as separators and are not part of the text itself.

The 09 marks the end beginning of a chapter, like this:
Note that: The library starts with a dummy 09 so that the first keyword line can be found.

• 09 chapter-1 09 chapter-2 09 last-chapter 09

The 0D marks the end of a line:

• line-1 0D line-2 0D last-line 0D

The first line of each library chapter starts with case insensitive keyword(s) separated by spaces. The word CHAPTER builds this the first line, and provides this line with a backslash to prevent the keywords for being executed while loading a chapter. Then it adds all source code until the %% marker is found. The end of each chapter is marked by 09 The end of the library is kept in a pointer that is updated when we extend the library.

chapter 2TUCK
\ Copy top double below second
: 2TUCK   2swap 2over ;     ( x1 x2 x3 x4 -- x3 x4 x1 x2 x3 x4 )
%%
 
chapter 2ROT
\ Rotate third double to top of stack
: 2ROT    2>r 2swap  2r> 2swap ;
%%
 
chapter -2ROT
\ Rotate top double to third double position on the stack
: -2ROT   2swap 2>r  2swap 2r> ;
%%

The above library chapters leave the following ASCII structure in Flash memory.
When after the <09> there is no more text, it's the end of the library.

\ 2TUCK<0D>
\ Copy top double below second<0D>
: 2TUCK   2swap 2over ;     ( x1 x2 x3 x4 -- x3 x4 x1 x2 x3 x4 )<0D>
<09>

\ 2ROT<0D>
\ Rotate third double to top of stack<0D>
: 2ROT    2>r 2swap  2r> 2swap ;<0D>
<09>

\ -2ROT<0D>
\ Rotate top double to third double position on the stack<0D>
: -2ROT   2swap 2>r  2swap 2r> ;<0D>
<09>

Function: NEEDED   ( a +n -- i*x )
    a) Save the string a +n and make the string uppercase
    b) If this string is already present in the dictionary, do nothing
    c) Start searching the library for this string
    d) When a keyword is found load the source code section until 09 is found
    e) When a keyword is not found issue an error message
    
Function: NEED     ( "name" -- i*x )
    a) Parse the next word form the input stream and perform the function of NEEDED

Function: .LIB     ( -- )
    a) Scan the library for a 09
    b) When it's not the last, print the found library chapter/section header

Function: OPEN-LIB    ( -- )
    Open the library by reading the last incomplete file sector to the 
    sector buffer. Adapt the library write administration in such a way
    that new source code will be added behind whats read from Flash.
    When the library is empty, lay down the start of a section header 
    with a 0D & 09 character.

Function: CLOSE-LIB   ( -- )
    Close the library, writing the last added code (incomplete sector)
    Update the end of library pointer

Function: WIPE-LIB    ( -- )
    Erase a stored library completely, restore the end of library pointer

Function: CHAPTER     ( -- )
    Add a new library section, first add the section header.
    Note the given keywords in uppercase, sepatated by spaces and ended 
    with a 0D. Read and store the Forth source code behind it until the 
    end of source marker %% was found

This sample is taken from the noForth t library mechanism. Here the library is stored in the remaining flash that is not needed by the noForth binaries. For readability some noForth specific words are replaced.

  create KEYWORD  20 allot  \ Hold keyword
  1008,1000 constant LIB    \ Library start address
  LIB value LIBHERE         \ Current end address of library
 
: LIB-FIND    ( a +n –- sa ) \ a,+n=name, sa=begin-source-section
    keyword place           \ Save keyword
    keyword count upper     \ Convert to uppercase
    libhere  lib            \ Library address range
    begin
        2dup > 0= throw 2dup \ Nothing found?
        0D scan nip over 1+ \ Get line with keywords, skip \
        begin
        2dup > while        \ Line not done?
            bl skip dup >r  \ Skip leading spaces
            bl scan         \ After keyword
            r@  over r> -   \ Keyword length
            keyword count s<> 0= \ Keyword found, leave source address
            if  2drop nip exit
            then
        repeat
        2drop  09 scan  1+  \ Find library section, skip 09
    again ;
 
: LIB-REFILL  ( source-id –- f ) 
    to ib  false            \ Start of new line
    ib c@ 09 = ?exit        \ End of source section, ready
    ib FF + ib  0D scan     \ Find 0D (end of current line)
    dup ib - to #ib         \ Calc. & save line length
    1+ to source-id  drop   \ Save start of next line (behind 0D)
    >in !  true  ;          \ Refill succeeded
 
: LIB-LOAD    ( a –- i*x ) 
    ?dup 0= ?exit           \ Do nothing when zero
    @input >r 2>r           \ Save current input source
    to source-id            \ Set new input source
    #ib >in !  interpret    \ Force a REFILL when loading source section
    2r> r> !input ;         \ ib #ib,>in@ source-id restore input source
 
: NEEDED      ( a +n –- i*x ) 
    ['] lib-refill  to 'refill   \ Add library REFILL
    LIB-FIND keyword find nip 0= \ in the current forth search order
    and lib-load ;
 
: NEED        ( a +n –- i*x )   bl word count  needed ;
 
: .LIB        ( –- )      \ Show library contents by printing keyword lines
    libhere  lib                 \ Lib. range
    begin  cr
        20 for
            1+ 1+  2dup > 0= if  \ Skip backslash, not past end of file?
                2drop rdrop exit \ Ready
            then
            dup >r  0D scan      \ Get end of keyword line
            r@ over r> - type    \ Show keyword line
            28 hor - 0 max spaces \ In fixed column size
            hor 28 > if cr then
            09 scan  1+          \ Find section marker
        next
    key bl <> until  2drop ;

Note that: This sample code uses calls to the built-in ROM API functions.
It uses them for reading, writing and erasing flash memory.

10000000 constant XIP        \ Start of XIP memory
 
create BUFFER  180 allot     \ Sector buffer with overflow (noForth t)
0        value PTR           \ Buffer index
: LC,    buffer ptr + c!  incr ptr ;  ( b -- )    \ Compile a byte in the library buffer
: LM,    bounds ?do  i c@ lc,  loop ; ( a +n -- ) \ Compile the string a +n in the library buffer
 
: LIBWRITE      ( +n -- )   \ Write library sector
    libhere xip - buffer 100 write-flash \ Write lib. sector to flash
    dup +to libhere   negate +to ptr    \ To next lib. block & correct pointer
    buffer 100 FF fill                  \ Erase first buffer
    buffer 100 + buffer ptr move ;      \ Move overflow to sector buffer
 
: BUFFER-FULL   ( -- )      \ Buffer overflow, write & restore
    ptr FF > if  100 libwrite  then ;
 
: ADD-LIB       ( text -- ) \ Add library section, save it when a buffer is full
    begin   buffer-full                 \ Buffer overflow, write & restore
            refill drop                 \ Read new line
    ib 2 s" %%" s<> while               \ No (%%) delimiter?
         ib #ib lm, 0D lc,              \ Store line
    repeat  refill drop ;               \ Read next line
 
: (-BL)         ( -- )
    parea  bl skip nip  ib - >in ! ;    \ Skip leading spaces in IB
 
: CHAPTER       ( text -- )  \ Contruct new library section
    s" \ " lm,                      \ New lib. header
    begin
        (-bl) bl parse              \ Find keywords
    ?dup while
        2dup upper lm,  bl lc,      \ Store uppercase in buffer
    repeat  drop  0D lc,            \ Add formfeed when done
    add-lib  09 lc, ;
 
: OPEN-LIB      ( -- )  \ Open a lib. for writing, read incomplete lib. sector too!
    libhere lib <> if               \ Lib. not empty?
        libhere 100 /mod  100 *     \ Get previous sector & ptr length
        dup to libhere              \ Correct lib. pointer & calc. XIP address
        buffer 100 move  to ptr  {w \ Read uncomplete sector to buffer, open flash
    then  0 to ptr  {W ;            \ First lib. entry, open flash
 
: CLOSE-LIB     ( -- )      \ Close library, save unfinshed buffer too
    buffer-full  ptr libwrite  W} ; \ Write last sector if any & close flash
 
: WIPE-LIB      ( -- )          \ Remove previous stored library from flash
    lib xip -                   \ Convert to start sector address
    libhere lib -  FF000 and    \ Convert to erase sector length, max. 1 Mbyte
    1000 +  {W wipe-flash W}    \ Erase one sector extra
    lib to libhere ;            \ And reset library pointer

This examples shows how many different code parts can be used inside the library.

1. Just a version message printing some strings in a script
2. Interpret some noForth commands as script adapting a pointer
3. The addition of some high level routines, the VIEW function
4. Again a script, but with numeric input from the stack, changing the noForth configuration. It includes a test of the changed part.

open-lib
 
chapter version versie vsn
cr .(    NEED version 0.32     )
cr .(   Library version 0.22   )
cr .( Size is about 174 kBytes )
%%
 
chapter RESTORE-LIB
v: inside   \ Restore LIBHERE in case it got lost
    libhere hx 40000 +  lib   hx FF scan  nip to libhere
    cr .( Libhere ) libhere u.
    cr .( Size ) libhere lib - dm . .( bytes )
    freeze
v: fresh
%%
 
chapter VIEW
( A library consists of 09 {tab}, 0D {cr} and ASCII chars )
( ranging from blank to ~ others chars are not allowed )
v: inside also  definitions \ Show the library source code of a chapter
: .LINE     ( a1 -- a2 ch ) begin c@+ dup bl < 0= while emit repeat ;
: .DIVIDER  ( -- )          cr  10 for ." {} " next  cr ;
 
: LIBTYPE   ( a -- )
    begin
        10 0 do                         \ Max. 16 lines at a time
            cr .line 09 =               \ End of source chapter?
            if  .divider leave  then    \ Show divider & ready
        loop
    dup libhere < while                 \ More library source to be done?
        key bl <> if drop exit then     \ Yes, ask key, stop on non space
    repeat  drop ;
 
v: extra definitions
: VIEW      ( ccc -- )          bl-word count  lib-find libtype ;
v: fresh
%%
 
chapter PIN  SQUERY
( GPIO -- ) \ Change GPIO pin for S?
need [IF]
dup dm 30 2 within [if]  drop  dm 24  [then] \ Invalid switch pin?
1 cfg 1+  c!        \ GPIO-xx for S?
4 cfg @ abs 4 cfg ! \ Make sure to (re)start the second image
config
cr .( Test S? ) s? .
%%
 
chapter 12MHZ
\ change clock frequency
dm 12       0 cfg ! \ Set frequency in MHz
4 cfg @ abs 4 cfg ! \ Make sure to (re)start the second image
config              \ Test new configuration
%%
 
close-lib

When displayed the library chapters look like this:

\ VERSION VERSIE VSN
cr .(    NEED version 0.33     )
cr .(   Library version 0.22   )
cr .( Size is about 174 kBytes )
 
    \ RESTORE-LIB
v: inside   \ Restore LIBHERE in case it got lost
    libhere hx 40000 +  lib   hx FF scan  nip to libhere
    cr .( Libhere ) libhere u.
    cr .( Size ) libhere lib - dm . .( bytes )
    freeze
v: fresh
 
    \ VIEW
( A library consists of 09 {tab}, 0D {cr} and ASCII chars )
( ranging from blank to ~ others chars are not allowed )
v: inside also  definitions \ Show the library source code of a section
: .LINE     ( a1 -- a2 ch ) begin c@+ dup bl < 0= while emit repeat ;
: .DIVIDER  ( -- )          cr  10 for ." {} " next  cr ;
 
: LIBTYPE   ( a -- )
    begin
        10 0 do                         \ Max. 16 lines at a time
            cr .line 09 =               \ End of source section?
            if  .divider leave  then    \ Show divider & ready
        loop
    dup libhere < while                 \ More library source to be done?
        key bl <> if drop exit then     \ Yes, ask key, stop on non space
    repeat  drop ;
 
v: extra definitions
: VIEW      ( ccc -- )          bl-word count  lib-find libtype ;
v: fresh
 
    \ PIN SQUERY
( GPIO -- ) \ Change GPIO pin for S?
need [IF]
dup dm 30 2 within [if]  drop  dm 24  [then] \ Invalid switch pin?
1 cfg 1+  c!        \ GPIO-xx for S?
4 cfg @ abs 4 cfg ! \ Make sure to (re)start the second image
config
cr .( Test S? ) s? .
 
    \ 12MHZ
\ change clock frequency
dm 12       0 cfg ! \ Set frequency in MHz
4 cfg @ abs 4 cfg ! \ Make sure to (re)start the second image
config              \ Test new configuration

Other implementations