X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?p=forth.jl.git;a=blobdiff_plain;f=src%2Flib.4th;h=955cadfe236e34a1c286d4e98c9f5659b5245676;hp=b7cd560d2a512ad17797e8bcd29b48eec5e53239;hb=d2b2b3e5b33f882c18c9e7cf8c6623f4e863c2dd;hpb=21567de9ac591909bb28a454b03615a473917327 diff --git a/src/lib.4th b/src/lib.4th index b7cd560..955cadf 100644 --- a/src/lib.4th +++ b/src/lib.4th @@ -1,37 +1,46 @@ -: / /MOD SWAP DROP ; -: MOD /MOD DROP ; +: \ IMMEDIATE + KEY + 10 = 0BRANCH [ -5 , ] +; \ We can now comment! -: '\n' 10 ; -: BL 32 ; +\ BASIC DEFINITIONS ---------------------------------------------------------------------- -: CR '\n' emit ; -: SPACE BL emit ; +: / /MOD SWAP DROP ; +: MOD /MOD DROP ; +: */ -ROT * SWAP / ; -: NEGATE 0 swap - ; +: NEGATE 0 SWAP - ; : TRUE -1 ; : FALSE 0 ; : NOT 0= ; -: LITERAL IMMEDIATE ' LIT , , ; +\ Translate a number of cells into memory units +\ (in our case 1 cell = 1 memory unit) +: CELLS ; + +\ Since the smallest unit of memory in our system is 64 bits and since strings +\ are stored as arrays of 64 bit integers, the character store/fetch words are +\ just aliases of the standard store/fetch words. +: C! ! ; +: C@ @ ; +: C, , ; + +: DEPTH PSP@ PSP0 @ - ; + +: '\n' 10 ; +: BL 32 ; + +: LITERAL IMMEDIATE ['] LIT , , ; -: ':' - [ - CHAR : - ] - LITERAL +: [CHAR] IMMEDIATE + CHAR + ['] LIT , , ; -: ';' [ CHAR ; ] LITERAL ; -: '(' [ CHAR ( ] LITERAL ; -: ')' [ CHAR ) ] LITERAL ; -: '"' [ CHAR " ] LITERAL ; -: 'A' [ CHAR A ] LITERAL ; -: '0' [ CHAR 0 ] LITERAL ; -: '-' [ CHAR - ] LITERAL ; -: '.' [ CHAR . ] LITERAL ; +: CR '\n' emit ; +: SPACE BL emit ; -\ While compiling, '[COMPILE] word' compiles 'word' if it would otherwise be IMMEDIATE. : [COMPILE] IMMEDIATE WORD \ get the next word FIND \ find it in the dictionary @@ -39,40 +48,19 @@ , \ and compile that ; -\ RECURSE makes a recursive call to the current word that is being compiled. -\ -\ Normally while a word is being compiled, it is marked HIDDEN so that references to the -\ same word within are calls to the previous definition of the word. However we still have -\ access to the word which we are currently compiling through the LATEST pointer so we -\ can use that to compile a recursive call. : RECURSE IMMEDIATE LATEST @ \ LATEST points to the word being compiled at the moment >CFA \ get the codeword , \ compile it ; -\ CONTROL STRUCTURES ---------------------------------------------------------------------- -\ -\ So far we have defined only very simple definitions. Before we can go further, we really need to -\ make some control structures, like IF ... THEN and loops. Luckily we can define arbitrary control -\ structures directly in FORTH. -\ -\ Please note that the control structures as I have defined them here will only work inside compiled -\ words. If you try to type in expressions using IF, etc. in immediate mode, then they won't work. -\ Making these work in immediate mode is left as an exercise for the reader. - -\ condition IF true-part THEN rest -\ -- compiles to: --> condition 0BRANCH OFFSET true-part rest -\ where OFFSET is the offset of 'rest' -\ condition IF true-part ELSE false-part THEN -\ -- compiles to: --> condition 0BRANCH OFFSET true-part BRANCH OFFSET2 false-part rest -\ where OFFSET if the offset of false-part and OFFSET2 is the offset of rest - -\ IF is an IMMEDIATE word which compiles 0BRANCH followed by a dummy offset, and places -\ the address of the 0BRANCH on the stack. Later when we see THEN, we pop that address -\ off the stack, calculate the offset, and back-fill the offset. +: DEBUGON TRUE DEBUG ! ; +: DEBUGOFF FALSE DEBUG ! ; + +\ CONTROL STRUCTURES ---------------------------------------------------------------------- + : IF IMMEDIATE - ' 0BRANCH , \ compile 0BRANCH + ['] 0BRANCH , \ compile 0BRANCH HERE @ \ save location of the offset on the stack 0 , \ compile a dummy offset ; @@ -84,7 +72,7 @@ ; : ELSE IMMEDIATE - ' BRANCH , \ definite branch to just over the false-part + ['] BRANCH , \ definite branch to just over the false-part HERE @ \ save location of the offset on the stack 0 , \ compile a dummy offset SWAP \ now back-fill the original (IF) offset @@ -93,42 +81,30 @@ SWAP ! ; -\ BEGIN loop-part condition UNTIL -\ -- compiles to: --> loop-part condition 0BRANCH OFFSET -\ where OFFSET points back to the loop-part -\ This is like do { loop-part } while (condition) in the C language : BEGIN IMMEDIATE HERE @ \ save location on the stack ; : UNTIL IMMEDIATE - ' 0BRANCH , \ compile 0BRANCH + ['] 0BRANCH , \ compile 0BRANCH HERE @ - \ calculate the offset from the address saved on the stack , \ compile the offset here ; -\ BEGIN loop-part AGAIN -\ -- compiles to: --> loop-part BRANCH OFFSET -\ where OFFSET points back to the loop-part -\ In other words, an infinite loop which can only be returned from with EXIT : AGAIN IMMEDIATE - ' BRANCH , \ compile BRANCH + ['] BRANCH , \ compile BRANCH HERE @ - \ calculate the offset back , \ compile the offset here ; -\ BEGIN condition WHILE loop-part REPEAT -\ -- compiles to: --> condition 0BRANCH OFFSET2 loop-part BRANCH OFFSET -\ where OFFSET points back to condition (the beginning) and OFFSET2 points to after the whole piece of code -\ So this is like a while (condition) { loop-part } loop in the C language : WHILE IMMEDIATE - ' 0BRANCH , \ compile 0BRANCH + ['] 0BRANCH , \ compile 0BRANCH HERE @ \ save location of the offset2 on the stack 0 , \ compile a dummy offset2 ; : REPEAT IMMEDIATE - ' BRANCH , \ compile BRANCH + ['] BRANCH , \ compile BRANCH SWAP \ get the original offset (from BEGIN) HERE @ - , \ and compile it after BRANCH DUP @@ -136,32 +112,115 @@ SWAP ! \ and back-fill it in the original location ; -\ UNLESS is the same as IF but the test is reversed. -\ -\ Note the use of [COMPILE]: Since IF is IMMEDIATE we don't want it to be executed while UNLESS -\ is compiling, but while UNLESS is running (which happens to be when whatever word using UNLESS is -\ being compiled -- whew!). So we use [COMPILE] to reverse the effect of marking IF as immediate. -\ This trick is generally used when we want to write our own control words without having to -\ implement them all in terms of the primitives 0BRANCH and BRANCH, but instead reusing simpler -\ control words like (in this instance) IF. : UNLESS IMMEDIATE - ' NOT , \ compile NOT (to reverse the test) + ['] NOT , \ compile NOT (to reverse the test) [COMPILE] IF \ continue by calling the normal IF ; -\ COMMENTS ---------------------------------------------------------------------- -\ -\ FORTH allows ( ... ) as comments within function definitions. This works by having an IMMEDIATE -\ word called ( which just drops input characters until it hits the corresponding ). +: DO IMMEDIATE + ['] LIT , -1 , [COMPILE] IF + ['] >R , ['] >R , + ['] LIT , HERE @ 0 , ['] >R , + HERE @ +; + +: ?DO IMMEDIATE + ['] 2DUP , ['] - , [COMPILE] IF + ['] >R , ['] >R , + ['] LIT , HERE @ 0 , ['] >R , + HERE @ +; + +: I RSP@ 3 - @ ; + +: J RSP@ 6 - @ ; + +: ?LEAVE IMMEDIATE + ['] 0BRANCH , 13 , + ['] R> , ['] RDROP , ['] RDROP , + ['] LIT , HERE @ 7 + , ['] DUP , ['] -ROT , ['] - , ['] SWAP , ['] ! , + ['] BRANCH , + 0 , +; + +: LEAVE IMMEDIATE + ['] LIT , -1 , + [COMPILE] ?LEAVE +; + +: +LOOP IMMEDIATE + ['] DUP , \ Store copy of increment + + ['] R> , ['] SWAP , ['] R> , ['] SWAP , ['] R> , ['] SWAP , ['] + , ['] 2DUP , ['] - , + ['] SWAP , ['] >R , ['] SWAP , ['] >R , ['] SWAP , ['] >R , + + \ Condition differently depending on sign of increment + ['] SWAP , ['] 0>= , [COMPILE] IF + ['] 0<= , + [COMPILE] ELSE + ['] 0> , + [COMPILE] THEN + + \ Branch back to begining of loop kernel + ['] 0BRANCH , HERE @ - , + + \ Clean up + ['] RDROP , ['] RDROP , ['] RDROP , + + \ Record address of loop end for any LEAVEs to use + HERE @ SWAP ! + + [COMPILE] ELSE + ['] 2DROP , \ Clean up if loop was entirely skipped (?DO) + [COMPILE] THEN +; + +: LOOP IMMEDIATE + ['] LIT , 1 , + [COMPILE] +LOOP +; + + +\ CASE ------------------------------------------------------------------------ + +: CASE IMMEDIATE + 0 \ push 0 to mark the bottom of the stack +; + +: OF IMMEDIATE + ['] OVER , \ compile OVER + ['] = , \ compile = + [COMPILE] IF \ compile IF + ['] DROP , \ compile DROP +; + +: ENDOF IMMEDIATE + [COMPILE] ELSE \ ENDOF is the same as ELSE +; + +: ENDCASE IMMEDIATE + ['] DROP , \ compile DROP + + \ keep compiling THEN until we get to our zero marker + BEGIN + ?DUP + WHILE + [COMPILE] THEN + REPEAT +; + + +\ COMMENTS ---------------------------------------------------------------------- + : ( IMMEDIATE 1 \ allowed nested parens by keeping track of depth BEGIN KEY \ read next character - DUP '(' = IF \ open paren? + DUP [CHAR] ( = IF \ open paren? DROP \ drop the open paren 1+ \ depth increases ELSE - ')' = IF \ close paren? + [CHAR] ) = IF \ close paren? 1- \ depth decreases THEN THEN @@ -169,72 +228,60 @@ DROP \ drop the depth counter ; -( - From now on we can use ( ... ) for comments. - - STACK NOTATION ---------------------------------------------------------------------- - - In FORTH style we can also use ( ... -- ... ) to show the effects that a word has on the - parameter stack. For example: - - ( n -- ) means that the word consumes an integer (n) from the parameter stack. - ( b a -- c ) means that the word uses two integers (a and b, where a is at the top of stack) - and returns a single integer (c). - ( -- ) means the word has no effect on the stack -) - ( Some more complicated stack examples, showing the stack notation. ) : NIP ( x y -- y ) SWAP DROP ; -: TUCK ( x y -- y x y ) DUP ROT ; +: TUCK ( x y -- y x y ) DUP -ROT ; : PICK ( x_u ... x_1 x_0 u -- x_u ... x_1 x_0 x_u ) 1+ ( add one because of 'u' on the stack ) PSP@ SWAP - ( add to the stack pointer ) @ ( and fetch ) ; +: ROLL ( x_u x_u-1... x_0 u -- x_u-1 ... x_0 x_u ) + 1+ DUP PICK SWAP ( x_u x_u-1 ... x_0 x_u u+1 ) + PSP@ 1- SWAP - PSP@ 2- SWAP + DO + i 1+ @ i ! + LOOP + SWAP DROP +; ( With the looping constructs, we can now write SPACES, which writes n spaces to stdout. ) : SPACES ( n -- ) - BEGIN - DUP 0> ( while n > 0 ) - WHILE - SPACE ( print a space ) - 1- ( until we count down to 0 ) - REPEAT - DROP + DUP 0> IF + 0 DO SPACE LOOP + ELSE + DROP + THEN ; ( Standard words for manipulating BASE. ) : DECIMAL ( -- ) 10 BASE ! ; : HEX ( -- ) 16 BASE ! ; -( - PRINTING NUMBERS ---------------------------------------------------------------------- - - The standard FORTH word . (DOT) is very important. It takes the number at the top - of the stack and prints it out. However first I'm going to implement some lower-level - FORTH words: - - U.R ( u width -- ) which prints an unsigned number, padded to a certain width - U. ( u -- ) which prints an unsigned number - .R ( n width -- ) which prints a signed number, padded to a certain width. - - For example: - -123 6 .R - will print out these characters: - - 1 2 3 - - In other words, the number padded left to a certain number of characters. +( Compute absolute value. ) +: ABS ( n -- |n| ) + dup 0< if + negate + then +; - The full number is printed even if it is wider than width, and this is what allows us to - define the ordinary functions U. and . (we just set width to zero knowing that the full - number will be printed anyway). +: MAX ( n m -- max ) + 2dup - 0< if + swap drop + else + drop + then +; - Another wrinkle of . and friends is that they obey the current base in the variable BASE. - BASE can be anything in the range 2 to 36. +: MIN ( n m -- max ) + 2dup - 0> if + swap drop + else + drop + then +; - While we're defining . &c we can also define .S which is a useful debugging tool. This - word prints the current stack (non-destructively) from top to bottom. -) +( PRINTING NUMBERS ---------------------------------------------------------------------- ) ( This is the underlying recursive definition of U. ) : U. ( u -- ) @@ -245,13 +292,447 @@ ( print the remainder ) DUP 10 < IF - '0' ( decimal digits 0..9 ) + [CHAR] 0 ( decimal digits 0..9 ) ELSE 10 - ( hex and beyond digits A..Z ) - 'A' + [CHAR] A THEN + EMIT ; +( This word returns the width (in characters) of an unsigned number in the current base ) +: UWIDTH ( u -- width ) + BASE @ / ( rem quot ) + ?DUP IF ( if quotient <> 0 then ) + RECURSE 1+ ( return 1+recursive call ) + ELSE + 1 ( return 1 ) + THEN +; + +: U.R ( u width -- ) + SWAP ( width u ) + DUP ( width u u ) + UWIDTH ( width u uwidth ) + ROT ( u uwidth width ) + SWAP - ( u width-uwidth ) + ( At this point if the requested width is narrower, we'll have a negative number on the stack. + Otherwise the number on the stack is the number of spaces to print. But SPACES won't print + a negative number of spaces anyway, so it's now safe to call SPACES ... ) + SPACES + ( ... and then call the underlying implementation of U. ) + U. +; + +: .R ( n width -- ) + SWAP ( width n ) + DUP 0< IF + NEGATE ( width u ) + 1 ( save a flag to remember that it was negative | width n 1 ) + -ROT ( 1 width u ) + SWAP ( 1 u width ) + 1- ( 1 u width-1 ) + ELSE + 0 ( width u 0 ) + -ROT ( 0 width u ) + SWAP ( 0 u width ) + THEN + SWAP ( flag width u ) + DUP ( flag width u u ) + UWIDTH ( flag width u uwidth ) + ROT ( flag u uwidth width ) + SWAP - ( flag u width-uwidth ) + + SPACES ( flag u ) + SWAP ( u flag ) + + IF ( was it negative? print the - character ) + [CHAR] - EMIT + THEN + + U. +; + +: . 0 .R SPACE ; + +: .S ( -- ) + [CHAR] < EMIT DEPTH U. [CHAR] > EMIT SPACE + PSP0 @ 1+ + BEGIN + DUP PSP@ 2 - <= + WHILE + DUP @ . + 1+ + REPEAT + DROP +; + +: U. U. SPACE ; + +( ? fetches the integer at an address and prints it. ) +: ? ( addr -- ) @ . ; + +( c a b WITHIN returns true if a <= c and c < b ) +: WITHIN + -ROT ( b c a ) + OVER ( b c a c ) + <= IF + > IF ( b c -- ) + TRUE + ELSE + FALSE + THEN + ELSE + 2DROP ( b c -- ) + FALSE + THEN +; + + +( STRINGS ---------------------------------------------------------------------- ) + + +( Block copy, however, is important and novel: ) +: CMOVE ( src dest length -- ) + + DUP 0<= IF + EXIT + THEN + + -ROT OVER - ( length src (dest-src) ) + -ROT DUP ROT + SWAP ( (dest-src) (src+length) src ) + + DO + I @ ( (dest-src) i@ ) + OVER I + ( (dest-src) i@ (dest-src+i) ) + ! ( (dest-src) ) + LOOP + + DROP +; + +( C, appends a byte to the current compiled word. ) +: C, + HERE @ C! + 1 HERE +! +; + +: S" IMMEDIATE ( -- addr len ) + STATE @ IF ( compiling? ) + ['] LITSTRING , ( compile LITSTRING ) + HERE @ ( save the address of the length word on the stack ) + 0 , ( dummy length - we don't know what it is yet ) + KEY DROP + BEGIN + KEY ( get next character of the string ) + DUP [CHAR] " <> + WHILE + C, ( copy character ) + REPEAT + DROP ( drop the double quote character at the end ) + DUP ( get the saved address of the length word ) + HERE @ SWAP - ( calculate the length ) + 1- ( subtract 1 (because we measured from the start of the length word) ) + SWAP ! ( and back-fill the length location ) + ELSE ( immediate mode ) + HERE @ ( get the start address of the temporary space ) + KEY DROP + BEGIN + KEY + DUP [CHAR] " <> + WHILE + OVER C! ( save next character ) + 1+ ( increment address ) + REPEAT + DROP ( drop the final " character ) + HERE @ - ( calculate the length ) + HERE @ ( push the start address ) + SWAP ( addr len ) + THEN +; + +: ." IMMEDIATE ( -- ) + [COMPILE] S" ( read the string, and compile LITSTRING, etc. ) + ['] TELL , ( compile the final TELL ) +; + +: .( + KEY DROP + BEGIN + KEY + DUP [CHAR] ) = IF + DROP ( drop the double quote character ) + EXIT ( return from this function ) + THEN + EMIT + AGAIN +; + + +( CONSTANTS AND VARIABLES ------------------------------------------------------ ) + +: CONSTANT + WORD HEADER ( make dictionary entry (the name follows CONSTANT) ) + DOCOL , ( append DOCOL (the codeword field of this word) ) + ['] LIT , ( append the codeword LIT ) + , ( append the value on the top of the stack ) + ['] EXIT , ( append the codeword EXIT ) +; + +: ALLOT ( n -- ) + HERE +! ( adds n to HERE, after this the old value of HERE is still on the stack ) +; + +: VARIABLE + CREATE + 1 CELLS ALLOT ( allocate 1 cell of memory, push the pointer to this memory ) +; + + +: VALUE ( n -- ) + WORD HEADER ( make the dictionary entry (the name follows VALUE) ) + DOCOL , ( append DOCOL ) + ['] LIT , ( append the codeword LIT ) + , ( append the initial value ) + ['] EXIT , ( append the codeword EXIT ) +; + +: TO IMMEDIATE ( n -- ) + WORD ( get the name of the value ) + FIND ( look it up in the dictionary ) + >DFA ( get a pointer to the first data field (the 'LIT') ) + 1+ ( increment to point at the value ) + STATE @ IF ( compiling? ) + ['] LIT , ( compile LIT ) + , ( compile the address of the value ) + ['] ! , ( compile ! ) + ELSE ( immediate mode ) + ! ( update it straightaway ) + THEN +; + +( x +TO VAL adds x to VAL ) +: +TO IMMEDIATE + WORD ( get the name of the value ) + FIND ( look it up in the dictionary ) + >DFA ( get a pointer to the first data field (the 'LIT') ) + 1+ ( increment to point at the value ) + STATE @ IF ( compiling? ) + ['] LIT , ( compile LIT ) + , ( compile the address of the value ) + ['] +! , ( compile +! ) + ELSE ( immediate mode ) + +! ( update it straightaway ) + THEN +; + +( Fill u ints, starting at a, with the value b ) +: FILL ( a u b -- ) + -ROT OVER + SWAP ?DO + DUP I ! + LOOP + DROP +; + +: ERASE ( a u -- ) + 0 FILL +; + +( PRINTING THE DICTIONARY ------------------------------------------------------ ) + +: ID. + 1+ ( skip over the link pointer ) + DUP @ ( get the flags/length byte ) + F_LENMASK AND ( mask out the flags - just want the length ) + + BEGIN + DUP 0> ( length > 0? ) + WHILE + SWAP 1+ ( addr len -- len addr+1 ) + DUP @ ( len addr -- len addr char | get the next character) + DUP 32 >= OVER 127 <= AND IF + EMIT ( len addr char -- len addr | and print it) + ELSE + BASE @ SWAP HEX + ." \x" 0 .R + BASE ! + THEN + SWAP 1- ( len addr -- addr len-1 | subtract one from length ) + REPEAT + 2DROP ( len addr -- ) +; + +: ?HIDDEN + 1+ ( skip over the link pointer ) + @ ( get the flags/length byte ) + F_HIDDEN AND ( mask the F_HIDDEN flag and return it (as a truth value) ) +; +: ?IMMEDIATE + 1+ ( skip over the link pointer ) + @ ( get the flags/length byte ) + F_IMMED AND ( mask the F_IMMED flag and return it (as a truth value) ) +; + +: WORDS + LATEST @ ( start at LATEST dictionary entry ) + BEGIN + ?DUP ( while link pointer is not null ) + WHILE + DUP ?HIDDEN NOT IF ( ignore hidden words ) + DUP ID. ( but if not hidden, print the word ) + SPACE + THEN + @ ( dereference the link pointer - go to previous word ) + REPEAT + CR +; + + +( FORGET ---------------------------------------------------------------------- ) + +: FORGET + WORD FIND ( find the word, gets the dictionary entry address ) + DUP @ LATEST ! ( set LATEST to point to the previous word ) + HERE ! ( and store HERE with the dictionary address ) +; + +( DUMP ------------------------------------------------------------------------ ) + +\ TODO! + + +( DECOMPILER ------------------------------------------------------------------ ) + +: CFA> + LATEST @ ( start at LATEST dictionary entry ) + BEGIN + ?DUP ( while link pointer is not null ) + WHILE + 2DUP SWAP ( cfa curr curr cfa ) + < IF ( current dictionary entry < cfa? ) + NIP ( leave curr dictionary entry on the stack ) + EXIT + THEN + @ ( follow link pointer back ) + REPEAT + DROP ( restore stack ) + 0 ( sorry, nothing found ) +; + +: SEE + WORD FIND ( find the dictionary entry to decompile ) + + ( Now we search again, looking for the next word in the dictionary. This gives us + the length of the word that we will be decompiling. (Well, mostly it does). ) + HERE @ ( address of the end of the last compiled word ) + LATEST @ ( word last curr ) + BEGIN + 2 PICK ( word last curr word ) + OVER ( word last curr word curr ) + <> ( word last curr word<>curr? ) + WHILE ( word last curr ) + NIP ( word curr ) + DUP @ ( word curr prev (which becomes: word last curr) ) + REPEAT + + DROP ( at this point, the stack is: start-of-word end-of-word ) + SWAP ( end-of-word start-of-word ) + + DUP >CFA @ CASE + DOCOL OF + \ Colon definition + [CHAR] : EMIT SPACE DUP ID. SPACE + DUP ?IMMEDIATE IF ." IMMEDIATE " THEN CR + ENDOF + DOVAR OF + \ Variable definition + ." Variable " DUP ID. CR + 2DROP EXIT + ENDOF + DOCON OF + \ Constant definition + ." Constant " DUP ID. CR + 2DROP EXIT + ENDOF + + \ Unknown codeword + ." Primitive or word with unrecognized codeword." CR + DROP 2DROP EXIT + ENDCASE + + ( begin the definition with : NAME [IMMEDIATE] ) + ( [CHAR] : EMIT SPACE DUP ID. SPACE + DUP ?IMMEDIATE IF ." IMMEDIATE " THEN CR 4 ) + + 4 SPACES + + >DFA ( get the data address, ie. points after DOCOL | end-of-word start-of-data ) + + ( now we start decompiling until we hit the end of the word ) + BEGIN ( end start ) + 2DUP > + WHILE + DUP @ ( end start codeword ) + + CASE + ['] LIT OF ( is it LIT ? ) + 1+ DUP @ ( get next word which is the integer constant ) + . ( and print it ) + ENDOF + ['] LITSTRING OF ( is it LITSTRING ? ) + [CHAR] S EMIT [CHAR] " EMIT SPACE ( print S" ) + 1+ DUP @ ( get the length word ) + SWAP 1+ SWAP ( end start+1 length ) + 2DUP TELL ( print the string ) + [CHAR] " EMIT SPACE ( finish the string with a final quote ) + + ( end start+1+len, aligned ) + 1- ( because we're about to add 4 below ) + ENDOF + ['] 0BRANCH OF ( is it 0BRANCH ? ) + ." 0BRANCH ( " + 1+ DUP @ ( print the offset ) + . + ." ) " + ENDOF + ['] BRANCH OF ( is it BRANCH ? ) + ." BRANCH ( " + 1+ DUP @ ( print the offset ) + . + ." ) " + ENDOF + ['] ['] OF ( is it ['] ? ) + ." ['] " + 1+ DUP @ ( get the next codeword ) + CFA> ( and force it to be printed as a dictionary entry ) + ID. SPACE + ENDOF + ['] EXIT OF ( is it EXIT? ) + ( We expect the last word to be EXIT, and if it is then we don't print it + because EXIT is normally implied by ;. EXIT can also appear in the middle + of words, and then it needs to be printed. ) + 2DUP ( end start end start ) + 1+ ( end start end start+1 ) + <> IF ( end start | we're not at the end ) + ." EXIT " + THEN + ENDOF + ( default case: ) + DUP ( in the default case we always need to DUP before using ) + CFA> ( look up the codeword to get the dictionary entry ) + ID. SPACE ( and print it ) + ENDCASE + + 1+ ( end start+1 ) + REPEAT + + [CHAR] ; EMIT CR + + 2DROP ( restore stack ) +; + + +( MEMORY ------------------------------------------------------------------ ) +: UNUSED ( -- cells ) + MEMSIZE HERE @ - ;