FORTH-79 STANDARD A PUBLICATION OF THE FORTH STANDARDS TEAM OCTOBER 1980 CONTENTS Page 0. FOREWORD 1 1. PURPOSE 1 2. SCOPE 1 3. ORGANIZATION 1 4. DEFINITION OF TERMS 2 5. REFERENCES 9 6. REQUIREMENTS 10 7. COMPLIANCE AND LABELING 11 8. USE 12 9. GLOSSARY NOTATION 13 10. REQUIRED WORD SET 15 11. EXTENSION WORD SETS 32 11.1 Double Number Word Set 32 11.2 Assembler Word Set 34 12. EXPERIMENTAL PROPOSALS 34 REFERENCE WORD SET FORTH-79 HANDY REFERENCE CARD FORTH-79 STANDARD A PUBLICATION OF THE FORTH STANDARDS TEAM OCTOBER 1980 The existence of a FORTH Standard does not in any respect preclude anyone, whether the individual has approved this Standard or not, from implementing, marketing, purchasing or using products, processes, or procedures not conforming to the Standard. FORTH Standards are subject to periodic review and users are cautioned to obtain the latest editions. 0. FOREWORD The computer language FORTH was created by Mr. Charles Moore as an extensible, multi-level environment containing elements of an operating system, a machine monitor, and facilities for program development and testing. This Standard is a direct descendant of FORTH-77, a work of the FORTH Users Group (Europe). 1. PURPOSE The purpose of this FORTH Standard is to allow transportability of standard FORTH programs in source form among standard FORTH systems. A standard program shall execute equivalently on all standard FORTH systems. 2. SCOPE This standard shall apply to any Standard FORTH program executing on any Standard FORTH system, providing sufficient computer resources (memory, mass storage) are available. 3. ORGANIZATION This standard consists of: 1) General Text 2) Definitions of Terms 3) Required Word Set 4) Extension Ward Sets Word sets may be subdivided for conceptual purposes by functions Nucleus Interpreter Compiler Devices Tradeoffs When conflicting choices must be made, the following order shall guide the Standards Team. 1) Functional correctness - known bounds, non-ambiguous. 2) Portability - repeatable results when transported among Standard systems. 3) Simplicity. 4) Naming clarity - uniformity of expression. Descriptive names are preferred over procedural, (i.e., [COMPILE] rather than 'C, and ALLOT rather than DP+! .) 5) Generality. 6) Execution speed. 7) Memory compactness. 8) Compilation speed. 9) Historical continuity. 10) Pronounceability. 11) Teachability. 4. DEFINITIONS OF TERMS These definitions, when in lower case, are terms used within this Standard. They present terms as specifically used within FORTH. address, byte An unsigned number that locates an 8-bit byte in a standard FORTH address space over {0..65,535}. It may be a native machine address or a representation on a virtual machine, locating the 'addr-th' byte within the virtual byte address space. Address arithmetic is modulo 65,536 without overflow. address, compilation The numerical value equivalent to a FORTH word definition, which is compiled for that definition. The address interpreter uses this value to locate the machine code corresponding to each definition. (May also be called the code field address.) address, native machine The natural address representation of the host computer. address, parameter field The address of the first byte of memory associated with a word definition for the storage of compilation addresses (in a colon-definition), numeric data and text characters. arithmetic All integer arithmetic is performed with signed 16 or 32 bit two's complement results, unless noted. block The unit of data from mass storage, referenced by block number. A block must contain 1024 bytes regardless of the minimum data unit read/written from mass storage. The translation from block number to device and physical record is a function of the implementation. block buffer A memory area where a mass storage block is maintained. byte An assembly of 8 bits. In reference to memory, it is the storage capacity for 8 bits. cell A 16-bit memory location. The n-th cell contains the 2n-th and (2n+1)-th byte of the FORTH address space. The byte order is presently unspecified. character A 7-bit number which represents a terminal character. The ASCII character set is considered standard. When contained in a larger field, the higher order bits are zero. compilation The action of accepting text words from the input stream and placing corresponding compilation addresses in a new dictionary entry. defining word A word that, when executed, creates a new dictionary entry. The new word name is taken from the input stream. If the input stream is exhausted before the new name is available, an error condition exists. Common defining words are: : CONSTANT CREATE definition See 'word definition'. dictionary A structure of word definitions in a computer memory. In systems with a text interpreter, the dictionary entries are organized in vocabularies to enable location by name. The dictionary is extensible, growing toward high memory. equivalent execution For the execution of a standard program, a set of non-tine dependent inputs will produce the same non-time dependent outputs on any FORTH Standard System with sufficient resources to execute the program. Only standard source code will be transportable. error condition An exceptional condition which requires action by the system other than the expected function. Actions may be: 1. ignore, and continue 2. display a message 3. execute a particular word 4. interpret a block 5. return control to the text interpreter A Standard System shall be provided with a tabulation of the action taken for all specified error conditions. General error conditions: 1. input stream exhausted before a required . 2. empty stack and full stack for the text interpreter. 3. an unknown word, not a valid number for the text interpreter. 4. compilation of incorrectly nested conditionals. 5. interpretation of words restricted to compilation. 6. FORGETing within the system to a point that removes a word required for correct execution. 7. insufficient space remaining in the dictionary. false A zero number represents the false condition flag. flag A number that may have two logical states, zero and non-zero. These are named 'true' = non-zero, and 'false' = zero. Standard word definitions leave 1 for true, 0 for false. glossary A set of word definitions given in a natural language describing the corresponding computer execution action. immediate word A word defined to automatically execute when encountered during compilation, which handles exception cases to the usual compilation. See IF LITERAL ." etc. input stream A sequence of characters available to the system, for processing by the text interpreter. The input stream conventionally may be taken from a terminal (via the terminal input buffer) and mass storage (via a block buffer). >IN and BLK specify the input stream. Words using or altering >IN and BLK are responsible for maintaining and restoring control of the input stream. interpreter, address The (set of) word definitions which interprets (sequences of) FORTH compilation addresses by executing the word definition specified for each one. interpreter, text The (set of) word definitions that repeatedly accepts a word name from the input stream, locates the corresponding dictionary entry, and starts the address interpreter to execute it. Text in the input stream interpreted as a number leaves the corresponding value on the data stack. When in the compile mode, the addresses of FORTH words are compiled into the dictionary for later interpretation by the address interpreter. In this case, numbers are compiled, to be placed on the data stack when later interpreted. Numbers shall be accepted unsigned or negatively signed, according to BASE. load The acceptance of text from a mass storage device and execution of the dictionary definition of the words encountered. This is the general method for compilation of new definitions into the dictionary. mass storage Data is read from mass storage in the form of 1024 byte blocks. This data is held in block buffers. When indicated as UPDATEd (modified) data will be ultimately written to mass storage. number When values exist within a larger field, the high order bits are zero. When stored in memory the byte order of a number is unspecified. type range minimum field bit 0..1 1 character 0..127 7 byte 0..255 8 number -32,768..32,767 16 positive number 0..32,767 16 unsigned number O..65,535 16 double number -2,147,483,648.. 2,147,483,647 32 positive double number 0..2,147,483,647 32 unsigned double number 0..4,294,967,295 32 When represented on the stack, the higher 16-bits (with sign) of a double number are most accessible. When in memory the higher 16-bits are at the lower address. Storage extends over four bytes toward high memory. The byte order within each 16 -bit field is unspecified. output, pictured The use of numeric output primitives, which convert numerical values into text strings. The operators are used in a sequence which resembles a symbolic 'picture' of the desired text format. Conversion proceeds from low digit to high, from high memory to low. program A complete specification of execution to achieve a specific function (application task) expressed in FORTH source code form. return The means of terminating text from the input stream. (Conventionally a null (ASCII 0) indicates end of text in the input stream. This character is left by the 'return' key actuation of the operator's terminal, as an absolute stopper to text interpretation.) screen Textual data arranged for editing. By convention, a screen consists of 16 lines (numbered 0 thru 15) of 64 characters each. Screens usually contain program source text, but may be used to view mass storage data. The first byte of a screen occupies the first byte of a mass storage block, which is the beginning point for text interpretation during a load. source definition Text consisting of word names suitable for execution by the text interpreter. Such text is usually arranged in screens and maintained on a mass storage device. stack, data A last in, first out list consisting of 16-bit binary values. This stack is primarily used to hold intermediate values during execution of word definitions. Stack values may represent numbers, characters, addresses, boolean values, etc. When the name 'stack' is used, it implies the data stack. stack, return A last in, first out list which contains the machine addresses of word definitions whose execution has not been completed by the address interpreter. As a word definition passes control to another definition, the return point is placed on the return stack. The return stack may cautiously be used for other values, such as loop control parameters, and for pointers for interpretation of text. string A sequence of 8-bit bytes containing ASCII characters, located in memory by an initial byte address and byte count. transportability This term indicates that equivalent execution results when a program is executed on other than the system on which it was created. See 'equivalent execution'. true A non-zero value represents the true condition flag. Any non- zero value will be accepted by a standard word as 'true'; all standard words return one when leaving a ' true' flag. user area An area in memory which contains the storage for user variables. variables, user So that the words of the FORTH vocabulary may be re-entrant (to different users), a copy of each system variable is maintained in the user area. vocabulary An ordered list of word definitions. Vocabulary lists are an advantage in reducing dictionary search time and in separating different word definitions that may carry the sane name. word A sequence of characters terminated by at least one blank (or 'return'). Words are usually obtained via the input stream, from a terminal or mass storage device. word definition A named FORTH execution procedure compiled into the dictionary. Its execution may be defined in terms of machine code, as a sequence of compilation addresses or other compiled words. If named, it nay be located by specifying this name and the vocabulary in which it is located. word name The name of a word definition. Standard names must be distinguished by their length and first thirty-one characters, and may not contain an ASCII null, blank, or 'return'. word set A group of FORTH word definitions listed by common characteristics. The standard word sets consist of: Required Word Set Nucleus Words Interpreter Words Compiler Words Device Words Extension Word Sets 32-bit Word Set Assembler Ward Set Included as reference material only: Reference Word Set word set, compiler Words which add new procedures to the dictionary or aid compilation by adding compilation addresses or data structures to the dictionary. word set, devices Words which allow access to mass storage and computer peripheral devices. word set, interpreter Words which support interpretation of text input from a terminal or mass storage by execution of corresponding dictionary entries, vocabularies, and terminal output. word set, nucleus The FORTH words generally defined in machine code that create the stacks and fundamental stack operators (virtual FORTH machine). word set, reference This set of words is provided as a reference document only, as a set of formerly standardized words and candidate words for standardization. word set, required The minimum words needed to compile and execute all Standard Programs. word, standard A named FORTH procedure definition, formally reviewed and accepted by the Standards Team. A serial number identifier {100..999} indicates a Standard Word. A functional alteration of a Standard Word will require assignment of a new serial number identifier. The serial number identifier has no required use, other than to correlate the definition name with its unique Standard definition. 5. REFERENCES The following documents are considered to be a portion of this Standard: American Standard Code for Information Interchange, American National Standards Institute, X3.4-1968 Webster's Collegiate Dictionary shall be used to resolve conflicts in spelling and English word usage. The following documents are noted as pertinent to the FORTH-79 Standard, but are not part of this Standard. FORTH-77, FORTH Users Group, FST-780314 FORTH-78, FORTH International Standards Team FORTH-79, Reference Word Set FORTH-79, Experimental Proposals 6. REQUIREMENTS 6.1 Documentation Requirements Each Standard System and Standard Program shall be accompanied by a statement of the minimum (byte) requirements for: 1. System dictionary space 2. Application dictionary space 3. Data stack 4. Return stack 5. Mass storage contiguous block quantity required 6. An operator's terminal. Each Standard System shall be provided with a statement of the system action upon each of the error conditions as identified in this Standard. 6.2 Testing Requirements The following host computer configuration is specified as a minimum environment for testing against this Standard. Applications may require different capacities. 1. 2000 bytes of memory for application dictionary 2. Data stack of 64 bytes 3. Return stack of 48 bytes 4. Mass storage capacity of 32 blocks, numbered 0 through 31 5. One ASCII input/output device acting as an operator's terminal. 7. COMPLIANCE AND LABELING The FORTH Standards Team hereby specifies the requirements for labeling of systems and applications so that the conditions for program portability may be established. A system may use the specified labeling if it complies with the terms of this Standard, and meets the particular Word Set definitions. A Standard Program (application) may use the specified labeling if it utilizes the specified standard system according to this Standard, and executes equivalently on any such system. FORTH Standard A system may be labeled 'FORTH-79 Standard' if it includes all of the Required Word Set in either source or object form, and complies with the text of this Standard. After executing "79-STANDARD" the dictionary must contain all of the Required Word Set in the vocabulary FORTH, as specified in this Standard. Standard Sub-set A system may be labeled 'FORTH-79 Standard Sub-set' if it includes a portion of the Required Word Set, and complies with the remaining text of this standard. However, no Required Word may be present with a non-standard definition. Standard with Extensions A system may be labeled 'FORTH-79 Standard with Standard Extensions)' if it comprises a FORTH-79 Standard System and one or more Standard Extension Word Set(s). The designation would be in the form: 'FORTH-79 Standard with Double-Number-Standard Extensions' 8. USE A FORTH Standard, program may reference only the definitions of the Required Word Set, and definitions which are subsequently defined in terms of these words. Furthermore, a FORTH Standard program must use the standard words as required by any conventions of this Standard. Equivalent execution must result from Standard programs. The FORTH system may share the dictionary space with the user's application, and the native addressing protocol of the host computer is beyond the scope of this Standard. Therefore, in a Standard program, the user may only operate on data which was stored by the application. No exceptions! A Standard Program may address: 1. parameter fields of variables, constants and DOES> words. A DOES> word's parameter field may only be addressed with respect to the address left by DOES> , itself. 2. dictionary space ALLOTed. 3. data in mass storage block buffers. (Note restriction in BLOCK on latest buffer addressing.) 4. the user area and PAD. A Standard Program may NOT address: 1. directly into the data or return stacks. 2. into a definition's name field, link field, or code field. 3. into a definition's parameter field if not stored by the application. Further usage requirements are expected to be added for transporting progran between standard systems. FORTH Standard definitions have a serial number assigned, in the range 100 thru 999. Neither a Standard System nor Standard Program may redefine these word names, within the FORTH vocabulary. 9. GLOSSARY NOTATION Order The Glossary definitions are listed in ASCII alphabetical order. Stack Notation The first line of each entry describes the execution of the definition: i.e., before -- after In this notation, the top of the stack is to the right. Words may also be shown in context when appropriate. Attributes Capitalized symbols indicate attributes of the defined words: C The word may only be used during compilation of a colon definition. I Indicates that the word is IMMEDIATE and will execute during compilation, unless special action is taken. U A user variable. Capitalization Word names as used within the dictionary are conveniently written in upper case characters. Within this Standard lower case will be used when reference is made to the run-time machine code, not directly accessible. Pronunciation The natural language pronunciation of word names is given in double quotes ("). Stack Parameters Unless otherwise stated, all reference to numbers apply to 16- bit signed integers. The implied range of values is shown as {from..to}. The content of an address is shown by double curly brackets, particularly for the contents of variables, i.e., BASE {{2..70}}. addr {0..65,535} A value representing the address of a byte, within the FORTH standard memory space. This addressed byte may represent the first byte of a larger data field in memory. byte {0..255} A value representing an 8 bit byte. When in a larger field, the higher bits are zero. char {0..127} A value representing a 7 bit ASCII character code. When in a larger field, the higher bits are zero. d {-2,147,483,648..2,147,483,647} 32 bit signed 'double' number. The most significant 16-bits, with sign, is most accessible on the stack. flag A numerical value with two logical states; 0 = false, non- zero = true. n {-32,768..32,767} 16 bit signed integer number. Any other symbol refers to an arbitrary signed 16-bit integer in the range {-32,768..32,767}, unless otherwise noted. Input Text An arbitrary FORTH word accepted from the input stream. This notation refers to text from the input stream, not to values on the data stack. If the input stream is exhausted before encountering , an error condition exists. 10. REQUIRED WORD SET The words of the Required Word Set are grouped to show like characteristics. No implementation requirements should be inferred from this grouping. Nucleus Words ! * */ */MOD + +! +loop - / /MOD 0< 0= 0> 1+ 1- 2+ 2- < = > >R ?DUP @ ABS AND begin C! C@ colon CMOVE constant create D+ D< DEPTH DNEGATE do does> DROP DUP else EXECUTE EXIT FILL I if J LEAVE literal loop MAX MIN MOD MOVE NEGATE NOT OR OVER PICK R> R@ repeat ROLL ROT semicolon SWAP then U* U/ until variable while XOR (note that lower case entries refer to just the run-time code corresponding to a compiling word.) Interpreter Words # #> #S ' ( -TRAILING . 79-STANDARD <# >IN ? ABORT BASE BLK CONTEXT CONVERT COUNT CR CURRENT DECIMAL EMIT EXPECT FIND FORTH HERE HOLD KEY PAD QUERY QUIT SIGN SPACE SPACES TYPE U. WORD Compiler Words +LOOP , ." : ; ALLOT BEGIN COMPILE CONSTANT CREATE DEFINITIONS DO DOES> ELSE FORGET IF IMMEDIATE LITERAL LOOP REPEAT STATE THEN UNTIL VARIABLE VOCABULARY WHILE [ [COMPILE] ] Device Words BLOCK BUFFER EMPTY-BUFFERS LIST LOAD SAVE-BUFFERS SCR UPDATE ! n addr -- 112 "store" Store n at addr. # ud1 -- ud2 158 "sharp" Generate from an unsigned double number d1, the next ASCII character which is placed in an output string. Result d2 is the quotient after division by BASE is maintained for further processing. Used between <# and #> . #> d -- addr n 190 "sharp-greater" End pictured numeric output conversion. Drop d, leaving the text address, and character count, suitable for TYPE. #S ud -- 0 0 209 "sharp-s" Convert all digits of an unsigned 32-bit number ud, adding each to the pictured numeric output text, until remainder is zero. A single zero is added to the output string if the number was initially zero. Use only between <# and #>. ' -- addr I,171 "tick" Used in the form: ' If executing, leave the parameter field address of the next word accepted from the input stream. If compiling, compile this address as a literal; later execution will place this value on the stack. An error condition exists if not found after a search of the CONTEXT and FORTH vocabularies. Within a colon-definition ' is identical to [ ' ] LITERAL. ( -- I,122 "paren" Used in the form: ( ccc) Accept and ignore comment characters from the input stream, until the next right parenthesis. As a word, the left parenthesis must be followed by one blank. It may freely be used while executing or compiling. An error condition exists if the input stream is exhausted before the right parenthesis. * n1 n2 -- n3 138 "times" Leave the arithmetic product of n1 times n2. */ n1 n2 n3 -- n4 220 "times-divide" Multiply n1 by n2, divide the result by n3 and leave the quotient n4. n4 is rounded toward zero. The product of n1 times n2 is maintained as an intermediate 32-bit value for greater precision than the otherwise equivalent sequence: n1 n2 * n3 / */MOD n1 n2 n3 -- n4 n5 192 "times-divide-mod" Multiply n1 by n2, divide the result by n3 and leave the remainder n4 and quotient n5. A 32-bit intermediate product is used as for */ . The remainder has the same sign as n1. + n1 n2 -- n3 121 "plus" Leave the arithmetic sum of n1 plus n2. +! n addr -- 157 "plus-store" Add n to the 16-bit value at the address, by the convention given for + . +LOOP n -- I,C,141 "plus-loop" Add the signed increment n to the loop index using the convention for +, and compare the total to the limit. Return execution to the corresponding DO until the new index is equal to or greater than the limit (n>0), or until the new index is less than the limit (n<0). Upon the exiting from the loop, discard the loop control parameters, continuing execution ahead. Index and limit are signed integers in the range {-32,768..32,767}. (Comment: It is a historical precedent that the limit for n<0 is irregular. Further consideration of the characteristic is unlikely.) , n -- 143 "comma" Allot two bytes in the dictionary, storing n there. - n1 n2 -- n3 134 "minus" Subtract n2 from n1 and leave the difference n3. -TRAILING addr n1 -- addr n2 148 "dash-trailing" Adjust the character count n1 of a text string beginning at addr to exclude trailing blanks, i.e., the characters at addr+n2 to addr+n1-1 are blanks. An error condition exists if n1 is negative. . n -- 193 "dot" Display n converted according to BASE in a free field format with one trailing blank. Display only a negative sign. ." I,133 "dot-quote" Interpreted or used in a colon definition in the form: ." ccc" Accept the following text from the input stream, terminated by " (double-quote). If executing, transmit this text to the selected output device. If compiling, compile so that later execution will transmit the text to the selected output device. At least 127 characters are allowed in the text. If the input stream is exhausted before the terminating double- quote, an error condition exists. / n1 n2 -- n3 178 "divide" Divide n1 by n2 and leave the quotient n3. n3 is rounded toward zero. /MOD n1 n2 -- n3 n4 198 "divide-mod" Divide n1 by n2 and leave the remainder n3 and quotient n4. n3 has the same sign as n1. 0< n -- flag 144 "zero-less" True if n is less than zero (negative) 0= n -- flag 180 "zero-equals" True if n is zero. 0> n -- flag 118 "zero-greater" True if n is greater than zero. 1+ n -- n+1 107 "one-plus" Increment n by one, according to the operation of + . 1- n -- n-1 105 "one-minus" Decrement n by one, according to the operation of - . 2+ n -- n+2 135 "two-plus" Increment n by two, according to the operation of + . 2- n -- n-1 129 "two-minus" Decrement n by two, according to the operation of - . 79-STANDARD 119 Execute assuring that a FORTH-79 Standard system is available, otherwise an error condition exists. : 116 "colon" A defining word executed in the form: : ... ; Select the CONTEXT vocabulary to be identical to CURRENT. Create a dictionary entry for in CURRENT, and set compile mode. Words thus defined are called 'colon- definitions'. The compilation addresses of subsequent words from the input stream which are not immediate words are stored in the dictionary to be executed when is later executed. IMMEDIATE words are executed as encountered. If a word is not found after a search of the CONTEXT and FORTH vocabularies, conversion and compilation of a literal number is attempted, with regard to the current BASE; that failing, an error condition exists . ; I,C,196 "semi-colon" Terminate a colon definition and stop compilation. If compiling from mass storage and the input stream is exhausted before encountering ; an error condition exists. < n1 n2 -- flag 139 "less-than" True if n1 is less than n2. -32768 32767 < must return true. -32768 0 < must be distinguished. <# 169 "less-sharp" Initialize pictured numeric output. The words: # #> #S <# HOLD SIGN can be used to specify the conversion of a double-precision number into an ASCII character string stored in right-to-left order. = n1 n2 -- flag 173 "equals" True if n1 is equal to n2. > n1 n2 -- flag 102 "greater-than" True if n1 is greater than n2. >IN -- addr U,201 "to-in" Leave the address of a variable which contains the present character offset within the input stream {{0..1023}} See: WORD ( ." FIND >R n -- C,200 "to-r" Transfer n to the return stack. Every >R must be balanced by a R> in the same control structure nesting level of a colon- definition. ? addr -- 194 "question-mark" Display the number at address, using the format of "." . ?DUP n -- n ( n ) 184 "query-dupe" Duplicate n if it is non-zero. @ addr -- n 199 "fetch" Leave on the stack the number contained at addr. ABORT 101 Clear the data and return stacks, setting execution mode. Return control to the terminal. ABS n1 -- n1 108 "absolute" Leave the absolute value of a number. ALLOT n -- 154 Add n bytes to the parameter field of the most recently defined word. AND n1 n2 -- n3 183 Leave the bitwise logical 'and' of n1 and n2. BASE -- addr U,115 Leave the address of a variable containing the current input- output numeric conversion base. {{2..70}} BEGIN I,C,147 Used in a colon-definition in the form: BEGIN ... flag UNTIL or BEGIN ... flag WHILE ... REPEAT BEGIN marks the start of a word sequence for repetitive execution. A BEGIN-UNTIL loop will be repeated until flag is true. A BEGIN-WHILE-REPEAT loop will be repeated until flag is false. The words after UNTIL or REPEAT will be executed when either loop is finished. flag is always dropped after being tested. BLK -- addr U,132 "b-l-k" Leave the address of a variable containing the number of the mass storage block being interpreted as the input stream. If the content is zero, the input stream is taken from the terminal. BLOCK n -- addr 191 Leave the address of the first byte in block n. If the block is not already in memory, it is transferred from mass storage into whichever memory buffer has been least recently accessed. If the block occupying that buffer has been UPDATEd (i.e. modified), it is rewritten onto mass storage before block n is read into the buffer. n is an unsigned number. If correct mass storage read or write is not possible, an error condition exists. Only data within the latest block referenced by BLOCK is valid by byte address, due to sharing of the block buffers. BUFFER n -- addr 130 Obtain the next block buffer, assigning it to block n. The block is not read from mass storage. If the previous contents of the buffer has been marked as UPDATEd, it is written to mass storage. If correct writing to mass storage is not possible, an error condition exists. The address left is the first byte within the buffer for data storage. n is an unsigned number. C! n addr -- 219 "c-store" Store the least significant 8-bits of n at addr. C@ addr -- byte 156 "c-fetch" Leave on the stack the contents of the byte at addr (with higher bits zero, in a 16-bit field). CMOVE addr1 addr2 n -- 153 "c-move" Move n bytes beginning at address addr1 to addr2. The contents of addr1 is moved first proceeding toward high memory. If n is zero nothing is moved. COMPILE C,146 When a word containing COMPILE executes, the 16-bit value following the compilation address of COMPILE is copied (compiled) into the dictionary. i.e., COMPILE DUP will copy the compilation address of DUP. COMPILE [ 0 , ] will copy zero. CONSTANT n -- 185 A defining word used in the form: n CONSTANT to create a dictionary entry for , leaving n in its parameter field. When is later executed, n will be left on the stack. CONTEXT -- addr U,151 Leave the address of a variable specifying the vocabulary in which dictionary searches are to be made, during interpretation of the input stream. CONVERT d1 addr1 -- d2 addr2 195 Convert to the equivalent stack number the text beginning at addr1+1 with regard to BASE. The new value is accumulated into double number d1, being left as d2. addr2 is the address of the first non-convertible character. COUNT addr -- addr+1 n 159 Leave the address addr+1 and the character count of text beginning at addr. The first byte at addr must contain the character count n. Range of n is {0..255}. CR 160 "c-r" Cause a carriage-return and line-feed to occur at the current output device. CREATE 239 A defining word used in the form: CREATE to create a dictionary entry for , without allocating any parameter field memory. When is subsequently executed, the address of the first byte of 's parameter field is left on the stack. CURRENT -- addr U,137 Leave the address of a variable specifying the vocabulary into which new word definitions are to be entered. D+ d1 d2 --- d3 241 "d-plus" Leave the arithmetic sum of d1 plus d2. D< d1 d2 -- flag 244 "d-less-than" True if d1 is less than d2. DECIMAL 197 Set the input-output numeric conversion base to ten. DEFINITIONS 155 Set CURRENT to the CONTEXT vocabulary so that subsequent definitions will be created in the vocabulary previously selected as CONTEXT. DEPTH -- n 238 Leave the number of the quantity of 16-bit values contained in the data stack, before n added. DNEGATE d -- -d 245 "d-negate" Leave the two's complement of a double number. DO n1 n2 -- I,C,142 Used in a colon-definition: DO ... LOOP or DO ... +LOOP Begin a loop which will terminate based on control parameters. The loop index begins at n2, and terminates based on the limit n1. At LOOP or +LOOP, the index is modified by a positive or negative value. The range of a DO-LOOP is determined by the terminating word. DO-LOOP may be nested. Capacity for three levels of nesting is specified as a minimum for standard systems. DOES> I,C,168 "does" Define the run-time action of a word created by a high-level defining word. Used in the form: : ... CREATE ... DOES> ... ; and then Marks the termination of the defining part of the defining word and begins the defining of the run-time action for words that will later be defined by . On execution of the sequence of words between DOES> and ; are executed, with the address of 's parameter field on the stack. DROP n -- 233 Drop the top number from the stack. DUP n -- n n 205 "dupe" Leave a copy of the top stack number. ELSE -- I,C,167 Used in a colon-definition in the form: IF ... ELSE ... THEN ELSE executes after the true part following IF. ELSE forces execution to skip till just after THEN. It has no effect on the stack. (see IF) EMIT char -- 207 Transmit character to the current output device. EMPTY-BUFFERS 145 Mark all block buffers as empty, without necessarily affecting their actual contents. UPDATEd blocks are not written to mass storage. EXECUTE addr -- 163 Execute the dictionary entry whose compilation address is on the stack. EXIT C,117 When compiled within a colon-definition, terminate execution of that definition, at that point. May not be used within a DO...LOOP. EXPECT addr n -- 189 Transfer characters from the terminal beginning at addr, upward, until a "return" or the count of n has been received. Take no action for n less than or equal to zero. One or two nulls are added at the end of text. FILL addr n byte -- 234 Fill memory beginning at address with a sequence of n copies of byte. If the quantity n is less than or equal to zero, take no action. FIND -- addr 203 Leave the compilation address of the next word name, which is accepted from the input stream. If that word cannot be found in the dictionary after a search of CONTEXT and FORTH leave zero. FORGET 186 Execute in the form: FORGET Delete from the dictionary (which is in the CURRENT vocabulary) and all words added to the dictionary after , regardless of their vocabulary. Failure to find in CURRENT or FORTH is an error condition. FORTH I,187 The name of the primary vocabulary. Execution makes FORTH the CONTEXT vocabulary. New definitions become a part of the FORTH until a differing CURRENT vocabulary is established. User vocabularies conclude by 'chaining' to FORTH, so it should be considered that FORTH is 'contained' within each user's vocabulary. HERE -- addr 188 Return the address of the next available dictionary location. HOLD char -- 175 Insert char into a pictured numeric output string. May only be used between <# and #> . I -- n C,136 Copy the loop index onto the data stack. May only be used in the form: DO ... I ... LOOP or DO ... I ... +LOOP IF flag -- I,C,210 Used in a colon-definition in the form: flag IF ... ELSE ... THEN or flag IF ... THEN If flag is true, the words following IF are executed and the words following ELSE are skipped. The ELSE part is optional. If flag is false, words between IF and ELSE, or between IF and THEN (when no ELSE is used), are skipped. IF-ELSE-THEN conditionals may be nested. IMMEDIATE 103 Marks the most recently made dictionary entry as a word which will be executed when encountered during compilation rather than compiled. J -- n C,225 Return the index of the next outer loop. May only be used within a nested DO-LOOP in the form: DO ... DO ... J ... LOOP ... LOOP KEY -- char 100 Leave the ASCII value of the next available character from the current input device. LEAVE C,213 Force termination of a DO-LOOP at the next LOOP or +LOOP by setting the loop limit equal to the current value of the index. The index itself remains unchanged, and execution proceeds normally until the loop terminating word is encountered. LIST n -- 109 List the ASCII symbolic contents of screen n on the current output device, setting SCR to contain n. n is unsigned. LITERAL n -- I,215 If compiling, then compile the stack value n as a 16-bit literal, which when later executed, will leave n on the stack. LOAD n -- 202 Begin interpretation of screen n by making it the input stream; preserve the locators of the present input stream (from >IN and BLK). If interpretation is not terminated explicitly it will be terminated when the input stream is exhausted. Control then returns to the input stream containing LOAD, determined by the input stream locators >IN and BLK. LOOP I,C,124 Increment the DO-LOOP index by one, terminating the loop if the new index is equal to or greater than the limit. The limit and index are signed numbers in the range {-32,768 ..32,767}. MAX n1 n2 -- n3 218 "max" Leave the greater of two numbers. MIN n1 n2 -- n3 127 "min" Leave the lesser of two numbers. MOD n1 n2 -- n3 104 Divide n1 by n2, leaving the remainder n3, with the same sign as n1. MOVE addr1 addr2 n -- 113 Move the specified quantity n of 16-bit memory cells beginning at addr1 into memory at addr2. The contents of addr1 is moved first. If n is negative or zero, nothing is moved. NEGATE n -- -n 177 Leave the two's complement of a number, i.e., the difference of zero less n. NOT flag1 -- flag2 165 Reverse the boolean value of flag1. This is identical to 0=. OR n1 n2 -- n3 223 Leave the bitwise inclusive-or of two numbers. OVER n1 n2 -- n1 n2 n1 170 Leave a copy of the second number on the stack. PAD -- addr 226 The address of a scratch area used to hold character strings for intermediate processing. The minimum capacity of PAD is 64 characters (addr through addr+63). PICK n1 -- n2 240 Return the contents of the n1-th stack value, not counting n1 itself. An error condition results for n less than one. 2 PICK is equivalent to OVER. {1..n} QUERY 235 Accept input of up to 80 characters (or until a 'return') from the operator's terminal, into the terminal input buffer. WORD may be used to accept text from this buffer as the input stream, by setting >IN and BLK to zero. QUIT 211 Clear the return stack, setting execution mode, and return control to the terminal. No message is given. R> -- n C,110 "r-from" Transfer n from the return stack to the data stack. R@ -- n C,228 "r-fetch" Copy the number on top of the return stack to the data stack. REPEAT -- I,C,120 Used in a colon-definition in the form: BEGIN ... WHILE ... REPEAT At run-time, REPEAT returns to just after the corresponding BEGIN. ROLL n -- 236 Extract the n-th stack value to the top of the stack, not counting n itself, moving the remaining values into the vacated position. An error condition results for n less than one. {1..n} 3 ROLL = ROT 1 ROLL = null operation ROT n1 n2 n3 -- n2 n3 n1 212 "rote" Rotate the top three values, bringing the deepest to the top. SAVE-BUFFERS 221 Write all blocks to mass-storage that have been flagged as UPDATEd. An error condition results if mass-storage writing is not completed. SCR -- addr U,217 Leave the address of a variable containing the number of the screen most recently listed. SIGN n -- C,140 Insert the ASCII "-" (minus sign) into the pictured numeric output string, if n is negative. SPACE 232 Transmit an ASCII blank to the current output device. SPACES n -- 231 Transmit n spaces to the current output device. Take no action for n of zero or less. STATE -- addr U,164 Leave the address of the variable containing the compilation state. A non-zero content indicates compilation is occurring, but the value itself may be installation dependent. SWAP n1 n2 -- n2 n1 230 Exchange the top two stack values. THEN I,C,161 Used in a colon-definition in the form: IF ... ELSE ... THEN or IF ... THEN THEN is the point where execution resumes after ELSE or IF (when no ELSE is present). TYPE addr n -- 222 Transmit n characters beginning at address to the current output device. No action takes place for n less than or equal to zero. U* un1 un2 -- ud3 242 "u-times" Perform an unsigned multiplication of un1 by un2, leaving the double number product ud3. All values are unsigned. U. un -- 106 "u-dot" Display un converted according to BASE as an unsigned number, in a free-field format, with one trailing blank. U/MOD ud1 un2 -- un3 un4 243 "u-divide-mod" Perform the unsigned division of double number ud1 by un2, leaving the remainder un3, and the quotient un4. All values are unsigned. U< un1 un2 -- flag 150 "u-less-than" Leave the flag representing the magnitude comparison of un1 < un2 where un1 and un2 are treated as 16-bit unsigned integers. UNTIL flag -- I,C,,237 Within a colon-definition, mark the end of a BEGIN-UNTIL loop, which will terminate based on flag. If flag is true, the loop is terminated. If flag is false, execution returns to the first word after BEGIN. BEGIN-UNTIL structures may be nested. UPDATE 229 Mark the most recently referenced block as modified. The block will subsequently be automatically transferred to mass storage should its memory buffer be needed for storage of a different block, or upon execution of SAVE-BUFFERS. VARIABLE 227 A defining word executed in the form: VARIABLE to create a dictionary entry for and allot two bytes for storage in the parameter field. The application must initialize the stored value. When is later executed, it will place the storage address on the stack. VOCABULARY 208 A defining word executed in the form: VOCABULARY to create (in the CURRENT vocabulary) a dictionary entry for , which specifies a new ordered list of word definitions. Subsequent execution of will make it the CONTEXT vocabulary. When becomes the CURRENT vocabulary (see DEFINITIONS), new definitions will be created in that list. In lieu of any further specification, new vocabularies 'chain' to FORTH. That is, when a dictionary search through a vocabulary is exhausted, FORTH will be searched. WHILE flag -- I,C,149 Used in the form: BEGIN ... flag WHILE ... REPEAT Select conditional execution based on flag. On a true flag, continue execution through to REPEAT, which then returns back to just after BEGIN. On a false flag, skip execution to just after REPEAT, exiting the structure. WORD char -- addr 181 Receive characters from the input stream until the non-zero delimiting character is encountered or the input stream is exhausted, ignoring leading delimiters. The characters are stored as a packed string with the character count in the first character position. The actual delimiter encountered (char or null) is stored at the end of the text but not included in the count. If the input stream was exhausted as WORD is called, then a zero length will result. The address of the beginning of this packed string is left on the stack. XOR n1 n2 -- n3 174 "x-or" Leave the bitwise exclusive-or of two numbers. [ I,125 "left-bracket" End the compilation mode. The text from the input stream is subsequently executed. See ] [COMPILE] I,C,179 "bracket-compile" Used in a colon-definition in the form: [COMPILE] Forces compilation of the following word. This allows compilation of an IMMEDIATE word when it would otherwise be executed. ] 126 "right-bracket" Sets the compilation mode. The text from the input stream is subsequently compiled. See [ 11. EXTENSION WORD SETS 11.1 DOUBLE NUMBER WORD SET 2! d addr -- "two-store" Store d in 4 consecutive bytes beginning at addr, as for a double number. 2@ addr -- d "two-fetch" Leave on the stack the contents of the four consecutive bytes beginning at addr, as for a double number. 2CONSTANT d -- "two-constant" A defining word used in the form: d 2CONSTANT to create a dictionary entry for , leaving d in its parameter field. When is later executed, d will be left on the stack. 2DROP d -- "two-drop" Drop the top double number on the stack. 2DUP d -- d d "two-dupe" Duplicate the top double number on the stack. 2OVER d1 d2 -- d1 d2 d1 "two-over" Leave a copy of the second double number on the stack. 2ROT d1 d2 d3 -- d2 d3 d1 "two-rote" Rotate the third double number to the top of the stack. 2SWAP d1 d2 -- d2 d1 "two-swap" Exchange the top two double numbers on the stack. 2VARIABLE "two-variable" A defining word used in the form: 2VARIABLE to create a dictionary entry of and assign four bytes for storage in the parameter field. When is later executed, it will leave the address of the first byte of its parameter field is placed on the stack. D+ d1 d2 -- d3 241 "d-plus" Leave the arithmetic sum of d1 and d2. D- d1 d2 -- d3 129 "d-minus" Subtract d2 from d1 and leave the difference d3. D. d -- 129 "d-dot" Display d converted according to BASE in a free field format, with one trailing blank. Display the sign only if negative. D.R d n -- "d-dot-r" Display d converted according to BASE, right aligned in an c character field. Display the sign only if negative. D0= d -- flag "d-zero-equals" Leave true if d is zero. D< d1 d2 -- flag 244 "d-less" True if d1 is less than d2. D= d1 d2 -- flag "d-equal" True if d1 equals d2. DABS d1 -- d2 "d-absolute" Leave as a positive double number d2, the absolute value of a double number, d1. {0..2,147,483,647} DMAX d1 d2 -- d3 "d-max" Leave the larger of two double numbers. DMIN d1 d2 -- d3 "d-min" Leave the smaller of two double numbers. DNEGATE d -- -d 245 Leave the double number two's complement of a double number, i.e., the difference 0 less d. DU< ud1 ud2 -- flag "d-u-less" True if ud1 is less than ud2. Both numbers are unsigned. 11.2 ASSEMBLER WORD SET ;CODE C,I,206 "semi-colon-code" Used in the form: : ... ;CODE Stop compilation and terminate a defining word . ASSEMBLER becomes the CONTEXT vocabulary. When is executed in the form: to define the new , the execution address of will contain the address of the code sequence following the ;CODE in . Execution of any will cause this machine code sequence to be executed. ASSEMBLER I,166 Select assembler as the CONTEXT vocabulary. CODE 111 A defining word used in the form: CODE ... END-CODE to create a dictionary entry for to be defined by a following sequence of assembly language words. ASSEMBLER becomes the context vocabulary. END-CODE Terminate a code definition, resetting the CONTEXT vocabulary to the CURRENT vocabulary. If no errors have occurred, the code definition is made available for use. 12. EXPERIMENTAL PROPOSALS No Experimental Proposals were submitted for publication. REFERENCE WORD SET This word set is furnished as a reference document. It is a set of formerly standardized words and candidate words for standardization. REFERENCE WORD SET FORTH-79 The Reference Word Set contain both Standard Word Definitions (with serial number identifiers in the range 100 through 999), and uncontrolled word definitions. Uncontrolled definitions are included for public reference of words that have present usage and/or are candidates for future standardization. No restrictions are placed on the definition or usage of uncontrolled words. However, use of these names for procedures differing from the given definitions is discouraged. !BITS n1 addr n2 -- "store-bits" Store the value of n1 masked by n2 into the equivalent masked part of the contents of addr, without affecting bits outside the mask. ** n1 n2 -- n3 "power" Leave the value of n1 to the power n2. +BLOCK n1 -- n2 "plus-block" Leave the sum of n1 plus the number of the block being interpreted, n1 and n2 are unsigned. -' -- ( addr ) flag "dash-tick" Used in the form: -' Leave the parameter field of beneath zero (false) if the name can be found in the CONTEXT vocabulary; leave only true if not found. --> I,131 "next-block" Continue interpretation on the next sequential block. May be used within a colon definition that crosses a block boundary. -MATCH addr1 n1 addr2 n2 -- addr3 f "dash-match" Attempt to find the n2-character string beginning at addr2 somewhere in the n1-character string beginning at addr1. Return the last+1 character address addr3 of the match point and a flag which is zero if a match exists. -TEXT addr1 n1 addr2 -- n2 "dash-text" Compare two strings over the length n1 beginning at addr1 and addr2. Return zero if the strings are equal. If unequal, return n2, the difference between the last characters compared: addr1(i) - addr2(i) .R n1 n2 -- "dot-r" Print n1 right aligned in a field of n2 characters, according to BASE. If n2 is less than 1, no leading blanks are supplied. /LOOP n -- "up-loop" A DO-LOOP terminating word. The loop index is incremented by the unsigned magnitude of n. Until the resultant index exceeds the limit, execution returns to just after the corresponding DO: otherwise, the index and limit are discarded. Magnitude logic is used. 1+! addr -- "one-plus-store" Add one to the 16-bit contents at addr. 1-! addr -- "one-minus-store" Subtract 1 from the 16-bit contents at addr. 2* n1 -- n2 "two-times" Leave 2*(n1). 2/ n1 -- n2 "two-divide" Leave (n1)/2. ;: C "semi-colon-oolon" Used to specify a new defining word: : ... ;: ... ; When is executed, it creates an entry for the new word . Later execution of will execute the sequence of words between ;: and ; , with the address of the first (if any) parameters associated with on the stack. ;S "semi-s" Stop interpretation of a block. For execution only. <> n1 n2 -- flag "not-equal" Leave true if n1 is not equal to n2. in defining words, in the form: : . . . ... ; and then When executes, . The sequence of words between established a parameter field for . When is later executed, the sequence of words following DOES> will be executed, with the parameter field address of on the data stack. < n1 -- n2 "byte-swap" Swap the high and low bytes within n1. >MOVE< addr1 addr2 n -- "byte-swap-move" Move n bytes beginning at addr1 to the memory beginning at addr2. During this move, the order of each byte pair is reversed. @BITS addr n1 -- n2 "fetch-bits" Return the 16-bits at addr masked by n1. ABORT" flag -- I,C "abort-quote" Used in a colon-definition in the form: ABORT" stack empty" If the flag is true, print the following text, till ". Then execute ABORT. AGAIN I,C,114 Effect an unconditional jump back to the start of a BEGIN- AGAIN loop. ASCII -- char (executing) -- (compiling) I,C Leave the ASCII character value of the next non-blank character in the input stream. If compiling, compile it as a literal, which will be later left when executed. ASHIFT n1 n2 -- n3 Shift the value n1 arithemetically n2 bits left if n2 is positive, shifting zeros into the least-significant bit positions. If n2 is negative, n1 is shifted right. Sign extension is to be consistent with the processor's arithmetic shift. B/BUF -- 1024 "bytes-per-buffer" A constant leaving 1024, the number of bytes per block buffer. BELL Activate a terminal bell or noise-maker as appropriate to the device in use. BL -- n 176 "b-l" Leave the ASCII character value for space (decimal 32). BLANKS addr n -- 152 Fill an area of memory over n bytes with the value for ASCII blank, starting at addr. If n is less than or equal to zero, take no action. C, n -- "c-comma" Store the low-order 8 bits of n at the next byte in the dictionary, advancing the dictionary pointer. CHAIN Used in the form: CHAIN Connect the CURRENT vocabulary to all definitions that might be entered into the vocabulary in the future. The CURRENT vocabulary may not be FORTH or ASSEMBLER. Any given vocabulary may only be chained once, but may be the object of any number of chainings. For example, every user-defined vocabulary may include the sequence: CHAIN FORTH COM n1 -- n2 Leave the one's complement of n1. CONTINUED n -- Continue interpretation at block n. CUR -- addr A variable pointing to the physical record number before which the tape is currently positioned. REWIND sets CUR=1. DBLOCK d -- addr "D-block" Identical to BLOCK but with a 32-bit block unsigned number. DPL -- addr "d-p-l" A variable containing the number of places after the fractional point for output conversion. If DPL contains zero, the last character output will be a decimal point. No point is output if DPL contains a negative value. DPL may be set explicitly, or by certain output words, but is unaffected by number input. DUMP addr n -- 123 List the contents of n addresses at addr. Each line of values may be preceded by the address of the first value. EDITOR I,172 The name of the editor vocabulary. When this name is executed, EDITOR is established as the CONTEXT vocabulary. END I,C,224 A synonym for UNTIL. ERASE addr n -- 182 Fill an area of memory over n bytes with zeros, starting at addr. If n is zero or less, take no action. FLD -- addr "f-l-d" A variable pointing to the field length reserved for a number during output conversion. FLUSH A synonym for SAVE-BUFFERS. H. n -- Output n as a hexadecimal integer with one trailing blank. The current base is unchanged. HEX -- 162 Set the numeric input-output conversion base to sixteen. I' -- n C "i-prime" Used within a colon-definition executed only from within a DO- LOOP to return the corresponding loop index. IFEND Terminate a conditional interpretation sequence begun by IFTRUE. IFTRUE flag -- Begin an IFTRUE ... OTHERWISE ... IFEND conditional sequence. These conditional words operate like IF ... ELSE ... THEN except that they cannot be nested, and are to be used only during interpretation. In conjunction with the words [ and ] they may be used within a colon-definition to control compilation, although they are not to be compiled. INDEX n1 n2 -- Print the first line of each screen over the range {n1..n2}. This displays the first line of each screen of source text, which conventionally contains a title. INTERPRET Begin interpretation at the character indexed by the contents of >IN relative to the block number contained in BLK, continuing until the input stream is exhausted. If BLK contains zero, interpret characters from the terminal input buffer. K -- n C Within a nested DO-LOOP, return the index of the second outer loop. LAST -- addr A variable containing the address of the beginning of the last dictionary entry made, which may not yet be a complete or valid entry. LINE n -- addr Leave the address of the beginning of line n for the screen whose number is contained in SCR. The range of n is {0..15}. LINELOAD n1 n2 -- Begin interpretation at line n1 of screen n2. LOADS n -- A defining word used in the form: n LOADS When is subsequently executed, block n will be loaded. MAP0 -- addr A variable pointing to the first location in the tape map. MASK n1 -- n2 Leave a mask of n1 most significant bits if n1 is positive, or n least significant bits if n1 is negative. MS n -- Delay for approximately n milliseconds. NAND n1 n2 -- n3 Hie one's complement of the logical and of n1 and n2. NOR n1 n2 -- n3 The one's complement of the logical or of n1 and n2. NUMBER addr -- n Convert the count and character string at addr, to a signed 32-bit integer, using the current base. If numeric conversion is not possible, an error condition exists. The string may contain a preceding negative sign. O. n -- Print n in octal format with one trailing blank. The value in base is unaffected. OCTAL Set the number base to 8. OFFSET -- addr 128 A variable that contains the offset added to the block number on the stack by BLOCK to determine the actual physical block number. The user must add any desired offset when utilizing BUFFER. OTHERWISE An interpreter-level conditional word. See IFTRUE. PAGE Clear the terminal screen or perform an action suitable to the output device currently active. READ-MAP Read to the next file mark on tape constructing a correspondence table in memory (the map) relating physical block position to logical block number. The tape should normally be rewound to its load point before executing READ- MAP. REMEMBER A defining word used in the form: REMEMBER Defines a word which, when executed, will cause and all subsequently defined words to be deleted from the dictionary. may be compiled into and executed from a colon definition. The sequence DISCARD REMEMBER DISCARD provides a standardized preface to any group of transient word definitions. REWIND Rewind the tape to its load point, setting CUR=1. ROTATE n1 n2 -- n3 Rotate the value n1 left n2 bits if n2 is positive, right n2 bits if n2 is negative. Bits shifted out of one end of the cell are shifted back in at the opposite end. S0 -- addr "s-zero" Returns the address of the bottom of the stack, when empty. SET n addr -- A defining word used in the form: n addr SET Defines a word which, when executed, will cause the value n to be stored at address. SHIFT n1 n2 -- n3 Logical shift n1 left n2 bits if n2 in positive, right if n2 is negative. Zeros are shifted into vacated bit positions. SP@ -- addr 214 "s-p-fetch" Return the address of the top of the stack, just before SP@ was executed. TEXT c -- Accept characters from the input stream, as for WORD, into PAD, blank-filling the remainder of PAD to 64 characters. THRU n1 n2 -- Load consecutively the blocks from n1 through n2. U.R un1 n2 -- 216 "u-dot-r" Output un1 as an unsigned number right justified in a field n2 characters wide. If n2 is smaller than the characters required for n1, no leading spaces are given. USER n -- A defining word used in the form: n USER which creates a user variable . n is the cell offset within the user area where the value for is stored. Execution of leaves its absolute user area storage address. VLIST List the word names of the CONTEXT vocabulary starting with the most recent definition. WHERE Output information about the status of FORTH, (e.g., after an error abort). Indicate at least the last word compiled and the last block accessed. \LOOP n -- I,C "down-loop" A DO-LOOP terminating word. The loop index is decremented by n and the loop terminated when the resultant index becomes equal to or less than the limit. Magnitude logic is used, and n must be positive.