Oakland CPM Archive/oakcpm.iso/sigm/vol236/lisp.doc

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                 LISP INTERPRETER APPLICATION NOTES


1. INTRODUCTION

     Thσá followinτá applicatioε note≤ givσ somσ oµá thσá detail≤ ì
necessar∙á t∩á properl∙á operatσ thσ LIS╨á interprete≥á whicΦá i≤ ì
implemented in the files named LISP.PAS/COM.
     A≤á i⌠á ha≤á no⌠á beeε possiblσ t∩ addres≤á iεá thσá presen⌠ ì
contex⌠ al∞ oµ thσ feature≤ whicΦ woulΣ bσ requireΣ t∩ maste≥ thσ ì
subject¼ interesteΣ reader≤ arσ inviteΣ t∩ refe≥ t∩ thσ availablσ ì
litterature for further details.
     This author has found most useful the following textbooks :

          Laurent SIKLOSSY - "Let's talk LISP" -
                    Prentice Hall, Inc., 1976

          Patrick H.WINSTON - Berthold K.P.HORN - "LISP" -
                    Addison-Wensley Pub.Co., 1981

          John ALLEN - "Anatomy of LISP" -
                    McGraw Hill Book Co., 1978.

     Thσá presen⌠á interprete≥á ha≤ beeε deriveΣá froφá thσá LIS╨ ì
interpreter available in ZUG vol.# 14.
     A≤á iε thσ origina∞ version¼á function≤ dealinτ witΦ number≤ ì
are not supported.


2. HOW TO RUN LISP

     Capita∞á letter≤á mus⌠ bσ useΣ fo≥ al∞ LIS╨á reserveΣá word≤ ì
(essentiall∙á name≤á oµá functions)║áá becausσá oµá thi≤á i⌠áá i≤ ì
recommended that capital letters be used throughout.

     To run the interpreter proceed as follows :

          1. Type LISP followed by a <cr>.
          2. Wait for the message R E A D Y to appear : this
             indicates that the interpreter is ready to eva-
             luate a LISP expression.
          3. Type the LISP expression to be evaluated on one
             or more successive lines (additional blanks  do
             not produce any effect).
             The expression must be preceeded by a left  pa-
             renthesis '(' and followed by a right parenthe-
             sis ')'.
             After having entered the LISP expression,  type
             twice <cr> to initiate the evaluation.
             (Ensure that the correct number of parentheses
             is entered otherwise the interpreter will refu-
             se to start the evaluation as it  expects  more
             input data).
          4. Once the evaluation is completed, the interpre-
             ter will print out the resulting expression.
è          5. After that, other evaluation cycles can be  in-
             troduced by repeating sequentially steps 3 and
             4.

     T∩á terminatσá thσá proces≤á anΣ returεá t∩á CP/═á typσá FI╬ ì
followed by two <cr>'s.


3. INITLISP

     INITLIS╨á i≤á thσ namσ oµ ß filσ whicΦ mus⌠ bσ availablσá oε ì
thσá samσá diskettσá a≤ thσ interprete≥ fo≥ thσá latte≥á t∩á worδ ì
properly.
     Upoε initiatioε oµ thσ interpreter¼ thσ content≤ oµ INITLIS╨ ì
i≤á reaΣ anΣ useΣ t∩ alte≥ thσ LIS╨ environmen⌠ b∙ addinτá user'≤ ì
defined variables (with their values) and/or functions.
     INITLIS╨ actuall∙ contain≤ element≤ oµ ß prograφ writteεá iε ì
LIS╨á anΣ an∙ oµ thσ character≤ employeΣ t∩ writσ ß LIS╨á prograφ ì
ma∙áá bσá used«áá  Howeve≥á tab≤á (anΣá perhap≤á othe≥á key≤á no⌠ ì
representinτ alphanumeriπ characters¼á dots¼ commas¼ spaces¼ etc⌐ ì
shoulΣá bσá avoideΣá a≤á the∙á ma∙á producσá unexpecteΣá results« ì
Further¼á INITLIS╨ mus⌠ bσ terminateΣ b∙ thσ atoφ FI╬ followeΣ b∙ ì
two <cr>'s to avoid reading beyond the eof.
     INITLIS╨ a≤ presenteΣ onl∙ contain≤ thσ atoφ FI╬ followeΣ b∙ ì
tw∩á <cr>'s«á Iε othe≥ word≤ INITLIS╨ wil∞ no⌠ affec⌠ a⌠ al∞á thσ ì
LISP environment upon activation of the interpreter.
     Thσá filσá INITLISP.STB¼á als∩ includeΣ fo≥ thσá purposσá oµ ì
demonstration¼ contain≤ ß numbe≥ oµ function≤ directl∙ writteε iε ì
LISP«á Afte≥á renaminτ thi≤ filσ INITLIS╨ (afte≥ havinτ saveΣ thσ ì
origina∞ INITLIS╨ fo≥ possiblσ re-use)¼á al∞ thesσ function≤ wil∞ ì
becomσá integra∞ par⌠ oµ thσ LIS╨ environmen⌠ upoε initiatioεá oµ ì
thσ interpreter«á  Hencσ the∙ caε bσ utilizeΣ a≤ the∙ werσ actua∞ ì
intrinsiπ functioε (witΦ somσ los≤ oµ efficiency).


4. TERMINOLOGY

     The following terms apply :

     a. SEX
        ┴á LISP-EXPRESSIO╬ o≥ SYMBOLIC-EXPRESSIO╬ (iε shor⌠á SEX⌐ ì
consist≤ oµ aε atoφ o≥ ß dotted-pai≥ o≥ ß list (see further on).

     b. ATOM
        Aεáá ATO═á consist≤á oµá ßá strinτá oµá u≡á t∩áá IDLENGT╚ ì
consecutivσ character≤ witΦ thσ exclusioε oµ '('¼á '.'¼ ')'¼ º '¼ ì
and <cr>.  (IDLENGTH is equal to 10).

     c. DOTTED-PAIR
        ┴ DOTTED-PAI╥ consist≤ oµ ß lef⌠ parenthesi≤ followeΣá b∙ ì
aεá atoφ o≥ anothe≥ dotted-pai≥ o≥ ß list¼á followeΣ b∙ ß period¼ ì
followeΣá b∙ aε atoφ o≥ ß dotted-pai≥ o≥ ß list¼á followeΣá b∙á ß ì
righ⌠ parenthesis.


è     d. LIST
        ┴á LIS╘á consist≤ oµ ß lef⌠ parenthesis¼á followeΣá b∙á ß ì
sequencσ oµ element≤ (atom≤ o≥ dotted-pair≤ o≥ list≤ separateΣ b∙ ì
one or more blanks), followed by a right parenthesis.
        ┴áá lis⌠á ma∙á contaiεá an∙á numbe≥á oµá element≤áá (zer∩ ì
included).

     e. SPECIAL ATOMS
        Atom T : denotes the truth value TRUE;
        Atom NIL : denotes the truth value FALSE.

     Atom≤ arσ alway≤ takeε a≤ representinτ variable≤ unles≤ the∙ ì
arσá preceedeΣá b∙á thσá atoφá QUOTE«áá Iεá thσá firs⌠á casσá thσ ì
interprete≥á attempt≤ t∩ evaluatσ theφ (iε othe≥ word≤ look≤á fo≥ ì
thσá valuσ associateΣ witΦ them⌐ whilσ iε thσ seconΣ casσ i⌠ doe≤ ì
not do that.


5. INTRINSIC FUNCTION SUPPORTED

     Thσá lis⌠á oµá thσá functioεsá whicΦá arσá supporteΣá b∙á thσ ì
interprete≥ anΣ ß brieµ descriptioε oµ wha⌠ eacΦ functioε doe≤ i≤ ì
giveε iε thσ following« Iε al∞ thσ example≤ whicΦ arσ giveε i⌠ i≤ ì
assumed that :
                    the value of X is the list (A B C)
                    the value of Y is the list (D E F)
                    the value of Z is the atom K.
     Iεá othe≥á word≤á i⌠á i≤ assumeΣ tha⌠á thσá followinτá threσ ì
statements have been executed :
                    (SETQ X (QUOTE(A B C)))
                    (SETQ Y (QUOTE(D E F)))
                    (SETQ Z (QUOTE K))

     Mos⌠á oµ thσ materia∞ whicΦ follow≤ ha≤ beeε takeε froφá thσ ì
text of Siklossy mentioned in the introduction.

     AND
          Number of arguments : any
          Arguments : any SEXes
          Value : NIL if the value of some argument is NIL,
                  otherwise T
          Example : (AND X Y) >>> T

     APPEND
          Number of arguments : 2
          Arguments : lists, when evaluated
          Value : the list of the SEXes representing the values
                  of the two arguments
          Example : (APPEND X Y) >>> (A B C D E F)

     ATOM
          Number of arguments : 1
          Arguments : any SEX
          Value : T if the arg is an atom; NIL otherwise
          Examples : (ATOM X) >>> NIL; (ATOM Z) >>> T
è
     CAR
          Number of arguments : 1
          Argument : nonempty list, when evaluated
          Value : first element of the list
          Example : (CAR X) >>> A

     CDR
          Number of arguments : 1
          Argument : nonempty list, when evaluated
          Valuσ ║á remaining part of list with first element
                   deleted
          Example : (CDR X) >>> (B C)

     CONS
          Number of arguments : 2
          Arguments : first, any SEX; second, any list (when
                      evaluated)
          Value : a list, such that its CAR is the first argu-
                  ment and its CDR the second argument
          Example : (CONS X Y) >>> ((A B C) D E F)

     COPY
          Number of arguments : 1
          Argument : any SEX
          Value : the argument
          Effec⌠ : a copy of the argument is added to the en-
                   vironment
ì
     DEFEXP (DEFine EXPression)
          Number of arguments : 1
          Use : to define a function and modify the environment
                accordingly; any such function always evaluates
                its arguments
          Examples : refer to file INITLISP.STB

     DEFFEXP (DEFine F-EXPression)
          Number of arguments : 1
          Use : same as DEFEXP, however the function does not
                evaluate its arguments

     DEFMAC (DEFine MACro)
          (NOT YET IMPLEMENTED)

     EQ
          Number of arguments : 2
          Arguments : two SEXes
          Value : T if the values of the 2 arguments are atoms
                  with the same name or if they are lists con-
                  tained in the same memory cells,
                  otherwise NIL
          Example : (EQ X Y) >>> NIL

     EQUAL
          Number of arguments : 2
è          Arguments : two SEXes
          Value : T if the values of the 2 arguments are equal,
                  otherwise NIL
          Example : (EQUAL X Y) >>> NIL

     EVAL
          Number of arguments : 1
          Argument : any SEX
          Value : the value of the value of the argument

     LAST
          Number of arguments : 1
          Argument : a list, when evaluated
          Value : the last SEX of the value of the argument
          Example : (LAST X) >>> C

     LENGTH
          Number of arguments : 1
          Argument : a list, when evaluated
          Value : the number of SEXes at the top level of the
                  value of the argument list
          Example : (LENGTH X) >>> 003

     LIST
          Number of arguments : any
          Arguments : any SEX
          Value : a list of the values of the arguments
          Example : (LIST X Y) >>> ((A B C)(D E F))

     NOT
          Number of arguments : 1
          Argument : any SEX
          Value : T if SEX has value NIL, otherwise NIL
          Example : (NOT X) >>> NIL

     NULL
          Same as NOT

     OR
          Number of arguments : any
          Arguments : any SEXes
          Value : NIL if no argument value is non-NIL,
                  otherwise T
          Example : (OR X Y) >>> NIL

     PROG2
          Number of arguments : 2
          Arguments : any SEXes
          Value : value of the second argument
          Side effect : the arguments are evaluated left to right

     PROGN
          Number of arguments : any
          Arguments : any SEXes
          Value : value of the last (rightmost argument)
è          Side effect : the arguments are evaluated left to right


     QUOTE
          Number of arguments : 1
          Argument : any SEX
          Value : the argument
          Example : (QUOTE X) >>> X

     REMOB (REMove OBject)
          Number of arguments : 1
          Argument : an atom
          Value : NIL (but basically irrelevant)
          Effect : the atom is permanently removed from the en-
          vironment

     REPLACEH (REPLACE Head)
          Number of arguments : 2
          Arguments : first : any SEX other than an atom;
                      second : any SEX
          Value : the value of the first argument with its CAR
                  replaced by the value of the second argument
          Side effect : the value of the first argument is modi-
                        fied permanently
          Example : (REPLACEH X Y) >>> ((D E F) B C)

     REPLACET (REPLACE Tail)
          Number of arguments : 2
          Arguments : as in REPLACEH
          Value : the value of the first argument with its CDR
                  replaced by the value of the second argument
          Side effect : as in REPLACEH
          Example : (REPLACET X Y) >>> (A D E F)

     REVERSE
          Number of arguments : 1
          Argument : a list, when evaluated
          Value : the value of the argument with its elements
                  reversed
          Example : (REVERSE X) >>> (C B A)

     SET
          Number of arguments : 2
          Arguments : first : must evaluate to an atom;
                      second : any SEX
          Value : the value of the second argument; the value
                  of the first argument has its value replaced
                  by this value of SET
          Side effect : the environment is permanently modified

     SETQ (SET Quote)
          Number of arguments : 2
          Arguments : first : an atom; second : any SEX
          Value : the value of the second argument; this value
                  becomes the value of the first argument
è          Side effect : the environment is permanently modified

     TRACE
          Number of arguments : 0
          Value : NIL (but basically irrelevant)
          Effect : all the functions will be traced

     UNTRACE
          Number of arguments : 0
          Value : NIL (but basically irrelevant)
          Effect : the functions will no longer be traced


6. ADDITIONAL FEATURES

     The following additional features are included :

          PROG control structure, allowing iterative programming
          style (limitations : GO and RETURN cannot be used to
          jump outside PROG);

          CONDitional expressions;

          LABEL for temporary function definitions;

          LAMBDA, FLAMBDA to introduce un-named functions evalua-
          ting (respectively non-evaluating) their arguments;

          FUNCTIO╬á construc⌠á t∩á dea∞á witΦá witΦá thσáá FUNAR╟ ì
          problem.


     Fo≥á al∞ oµ thσ abovσ feature≤ i⌠ i≤ recommendeΣ t∩ refe≥ t∩ ì
the available litterature on LISP.


7. ...TO TERMINATE

     AlthougΦ quitσ somσ testinτ ha≤ beeε performeΣ i⌠ canno⌠á bσ ì
excludeΣ tha⌠ thσ interprete≥ stil∞ contain≤ ß substantia∞ numbe≥ ì
of bugs. So I wish you good luck with it !
     ╔á wil∞á welcomσá an∙á querie≤ and/o≥á suggestion≤á iεá thi≤ ì
or any other respect.


Lanfranco EMILIANI
Maurits de Brauwweg 11
2597 KD Den Haag
The Netherlands