--- name: "lisp" section: "3gv" platform: "linux" package: "libgeomview-dev" version: "1.9.5-5" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/lisp/3gv" --- # lisp(3gv) [lisp(3gv)](/lisp/3gv.md) [lisp(3gv)](/lisp/3gv.md) NAME\ geomview lisp interpreter NOTE\ This document describes the geomview 1.3 lisp interpreter.\ This version is incompatible with previous versions in\ several ways. Since the previous one was used mostly just\ by Geometry Center staff, I am not going to write a docu-\ ment detailing the changes. The geomview lisp interpreter\ is not very well documented in general because I am\ strongly considering phasing it out and replacing it with\ a real lisp interpreter in a future version of geomview.\ If you have any questions about the current version or how\ to convert programs from an older version please contact\ me directly \[ mbp@geomtech.com \]. SYNOPSIS\ \#include "lisp.h" void LInit();\ Lake \* LakeDefine(FILE \*streamin, FILE \*streamout, void \*river);\ void LakeFree(Lake \*lake);\ LObject \* LNew(LType \*type, LCell \*cell);\ LObject \* LRefIncr(LObject \*obj);\ void LRefDecr(LObject \*obj);\ void LWrite(FILE \*fp, LObject \*obj);\ void LFree(LObject \*obj);\ LObject \* LCopy(LObject \*obj);\ LObject \* LSexpr(Lake \*lake);\ LObject \* LEval(LObject \*obj);\ LObject \* LEvalSexpr(Lake \*lake);\ LList \* LListNew();\ LList \* LListAppend(LList \*list, LObject \*obj);\ void LListFree(LList \*list);\ LList \* LListCopy(LList \*list);\ LObject \* LListEntry(LList \*list, int n);\ int LListLength(LList \*list);\ int LParseArgs(char \*name, Lake \*lake, LList \*args, ...);\ int LDefun(char \*name, LObjectFunc func, char \*help);\ void LListWrite(FILE \*fp, LList \*list);\ LInterest \* LInterestList(char \*funcname);\ LObject \* LEvalFunc(char \*name, ...);\ int LArgClassValid(LType \*type);\ void LHelpDef(char \*key, char \*message); LDEFINE(name, ltype, doc) LDECLARE((name, LBEGIN,\ ...,\ LEND)); Geometry Center Oct 22 1992 1 [lisp(3)](/lisp/3.md) [lisp(3)](/lisp/3.md) DESCRIPTION\ Geomview contains a minimal lisp interpreter for parsing\ and evaluating commands. This lisp interpreter is part of\ the "-loogutil" library and thus any program which links\ with this library may use the interpreter. This provides\ a simple but powerful way to build up a command language. This manual page assumes that you are familiar with the\ syntax of lisp. The first part describes the basics of\ using the interpreter. Some gory details that don't con-\ cern most users then follow. The main steps in using the lisp interpreter are 1\. call Linit() to initialize the interpreter\ 2\. make calls to LDefun(), one for each lisp function you want the\ interpreter to know about\ 3\. define the "i/o lake"\ 4\. parse input with calls to LSexpr() and evaluate the resulting\ lisp objects with LEval() (or use LEvalSexpr() to combine both steps). For example the following code defines a single function\ "f" and executes commands from standard input: \#include "lisp.h"\ Lake \*lake;\ LObject \*obj, \*val; LInit();\ LDefun("f", f, NULL);\ lake = LakeDefine(stdin, stdout, NULL);\ while (!feof(stdin)) {\ obj = LSexpr(lake);\ val = LEval(obj);\ LFree(obj);\ LFree(val);\ } The second argument to LDefun() is a function pointer;\ LDefun() sets up a correspondence between the string "f"\ and the function f, which is assumed to have been previ-\ ously declared. The section FUNCTION DEFINITIONS below\ gives the expected call syntax and behavior of such func-\ tions. (The third argument to LDefun() is a pointer to a\ string which documents the function and may be NULL if you\ don't care about documentation.) LakeDefine() defines an\ i/o lake; this is a generalization of the notion of an i/o\ stream. Most programs don't need to use the generaliza-\ tion, though, and can simply pass FILE pointers as LakeDe-\ fine()'s first two arguments and NULL as the third one.\ The section LAKES below gives the details for those who\ are interested. LSexpr() \[which stands for Lisp Symbolic\ EXPRession\] parses a single lisp expression from the lake,\ returning a lisp object which represents that expression. Geometry Center Oct 22 1992 2 [lisp(3)](/lisp/3.md) [lisp(3)](/lisp/3.md) The lisp object is returned as an LObject pointer, which\ points to an opaque structure containing a representation\ of the expression. LEval() then evaluates the object; it\ is during the call to LEval() that the action of the\ expression takes place. Note that the last two lines of\ code in this example could have been replaced by the sin-\ gle line LEval(LSexpr(lake)) or, more efficiently, by LEv-\ alSexpr(lake). FUNCTION DEFINITIONS\ The functions defined by calls to LDefun() are expected to\ have a certain call syntax; LEval() calls them when it\ encounters a call to the lisp function named with the cor-\ responding string. The macro LDEFINE is provided for\ declaring them. For example: LDEFINE(f, LSTRING, "(f a b) returns a string representing the0um of the integer a with the floating point number b.")\ {\ int a;\ float b;\ char buf\[20\], \*s; LDECLARE(("f", LBEGIN,\ LINT, &a,\ LFLOAT, &b,\ LEND));\ sprintf(buf,"%f",a+b);\ s = strdup(buf);\ return LNew(LSTRING, &s);\ } The important things about this function are: 1\. It is declared with the LDEFINE macro, the general syntax\ of which is LDEFINE(name, type, helpstr). name should be\ a valid C identifer and will be used to construct the actual\ name of the C function by prepending an 'L' and the name of\ the help string by prepending an 'H'. type should be a lisp\ object type identifier (see below) and determines the type\ of object that the function returns. helpstr is a documentation\ string. 2\. The use of the LDECLARE macro. More about this below. 3\. It returns an LObject \*. All lisp functions must actually\ return a value. If you don't care what value they return\ you can return one of the pre-defined values Lnil or Lt\ (and specify LVOID as the type in the LDEFINE header). This particular example is a function which takes two\ arguments, an int and a float, and returns a string object\ representing their sum. A lisp call to this function\ might look like "(f 1 3.4)". Geometry Center Oct 22 1992 3 [lisp(3)](/lisp/3.md) [lisp(3)](/lisp/3.md) The LDECLARE macro, defined in lisp.h, sets up the corre-\ spondence between variables in the C code and arguments in\ the lisp call to the function. Note that the arguments to\ LDECLARE are delimited by \*two\* pairs of parentheses (this\ is because C does not allow macros with a variable number\ of arguments; LDECLARE thus actually takes one argument\ which is a parenthesized list of an arbitrary number of\ items). The general usage of LDECLARE is LDECLARE(( name, LBEGIN,\ \,\ ...,\ LEND )); where name is the name of the function (as specified to\ LDefun()). \ is an argument specification, which\ in general consists of a lisp type identifier followed by\ an address. The identifier indicates the data type of the\ argument. The builtin type identifiers are LINT (inte-\ ger), LFLOAT (float), LSTRING (string), LLOBJECT (lisp\ object), and LLIST (lisp list). Applications may define\ additional types whose identifiers may also be used here;\ see the section CUSTOM LISP TYPES below for details.\ There may be any number of \'s; the last must be\ followed by the special keyword LEND. STOP HERE\ Most users of the lisp interpreter can stop reading this\ man page here. What follows is only used in advanced sit-\ uations. EVALUATION OF FUNCTION ARGUMENTS\ Normally the lisp interpreter evaluates function arguments\ before passing them to the function; to prevent this eval-\ uation from happening you can insert the special token\ LHOLD in an LDECLARE argument specification before the\ type keyword. For example LHOLD, LLIST, &list, specifies an unevalutated list argument. This feature is\ really useful only for LLIST, LLOBJECT, and array types\ (see below) since the other types evalutate to themselves. ARRAYS\ In general an \ in the LDECLARE call consists of a\ keyword followed by the address of a scalar data type.\ Since it is relatively common to use a lisp list to repre-\ sent an array of values, however, the special \\ keyword LARRAY is provided for dealing with them. It has\ a different syntax: it should be followed by a lisp type Geometry Center Oct 22 1992 4 [lisp(3)](/lisp/3.md) [lisp(3)](/lisp/3.md) identifier which specifies the type of the elements of the\ array and then by two addresses --- the address of an\ array and the address of an integer count. Upon entry to\ LDECLARE the count specifies how many elements may be\ written into the array. LDECLARE then modifies this num-\ ber to indicate the number of entries actually parsed.\ For example: LDEFINE(myfunc, ...)\ {\ float f\[2\];\ int fn = 2;\ LDECLARE(("myfunc", LEBGIN\ LHOLD, LARRAY, f, &fn,\ LEND));\ /\* at this point the value of fn has been modified to\ be the number of entries actually appearing in the\ list argument; and this number of values have been\ written into the array f. \*/\ ...\ } defines a function "myfunc" which takes a list of up to 2\ floats as its only argument. Valid calls to "myfunc"\ would be "(myfunc ())", "(myfunc (7))", and "(myfunc (7\ 8\))". Note the use of LHOLD; this is necessary because otherwise\ the lisp system would attempt to evaluate the list as a\ function call before passing it off to myfunc. OPTIONAL ARGUMENTS\ Normally the lisp interpreter will generate (to stderr) a\ reasonable error message if a function is called with\ fewer arguments than were specified in LDECLARE. Some\ functions, however, may have some arguments that are\ optional. You can define a function which takes optional\ arguments by putting the keyword LOPTIONAL after the last\ required argument in the LDECLARE call. Any arguments\ specified in the list after that are considered optional;\ the interpreter doesn't complain if they are not supplied.\ Note that all optional arguments must come after all\ required arguments. Normally excess arguments also elicit an error message.\ The LREST keyword allows control over this situation. If\ LREST is followed by a pointer to an LList \* variable,\ then trailing arguments are parsed, evaluated (unless\ LHOLD was used), and the list of them is stored in the\ given variable. (Note that the value is an LList, not an\ LObject of type LLIST -- if there are no excess arguments,\ the value is NULL, not an empty LLIST.) If LREST is fol-\ lowed by a NULL pointer, excess arguments are silently Geometry Center Oct 22 1992 5 [lisp(3)](/lisp/3.md) [lisp(3)](/lisp/3.md) ignored. LREST might be useful when a function's argument\ types are not known. It's not necessary to specify LEND\ after LREST. LISP OBJECTS\ The basic data type of the lisp interpreter is the lisp\ object; it is represented by an LObject pointer, which\ points to an opaque data structure. The functions for\ manipulating lisp objects (i.e. the object's methods) are: LNew(): creates a new lisp object of the given type with\ the given value. The "type" argument is one of the\ values LSTRING or LLIST, or a type pointer defining\ a custom object type (see CUSTOM OBJECT TYPES\ below).\ LRefIncr(): increments the reference count of a lisp\ object. The lisp interpreter uses the convention\ that when a procedure returns a lisp object, the\ caller owns the object and thus has responsibility\ for freeing it. LRefIncr() can be used to increment\ the reference count of an existing object about to\ be returned. New objects created by LNew() have\ their reference count initialized to 1 and hence do\ not need to be LRefIncr()'ed.\ LRefDecr(): decrements the reference count of a lisp\ object. This should probably not be called by\ application programs; it is used internally.\ LWrite(): writes a formatted string representation of a\ lisp object to a stream.\ LFree(): free the space assoicated with a lisp object\ LCopy(): construct a copy of a lisp object CUSTOM OBJECT TYPES\ In addition to the predefined lisp object types you may\ define your own custom types. This is done by construct-\ ing a structure containing various function pointers for\ manipulating objects of your new type. The address of\ this structure is then the type identifier for this type\ and may be used in LDECLARE \'s and in LNew()\ calls. (The type names LINT, LSTRING and the other\ builtin types are actually pointers to predefined struc-\ tures.) The structure is of type LType as defined in\ lisp.h: struct LType { /\* name of type \*/\ char \*name; /\* size of corresponding C type \*/\ int size; Geometry Center Oct 22 1992 6 [lisp(3)](/lisp/3.md) [lisp(3)](/lisp/3.md) /\* extract cell value from obj \*/\ int (\*fromobj)(/\* LObject \*obj, void \*x \*/); /\* create a new LObject of this type \*/\ LObject \*(\*toobj)(/\* void \*x \*/); /\* free a cell of this type \*/\ void (\*free)(/\* void \*x \*/); /\* write a cell value to a stream \*/\ void (\*write)(/\* FILE \*fp, void \*x \*/); /\* test equality of two cells of this type \*/\ int (\*match)(/\* void \*a, void \*b \*/); /\* pull a cell value from a va\_list \*/\ void (\*pull)(/\* va\_list \*a\_list, void \*x \*/); /\* parse an object of this type \*/\ LObject \*(\*parse)(/\* Lake \*lake \*/); /\* magic number; always set to LTypeMagic \*/\ int magic; }; The void \* pointers in the above point to objects of the\ type you are defining. For examples of how to define new\ types see the code in lisp.c that defines the string and\ list types. See also the file TYPES.DOC in the lisp\ source code directory for further details. LISTS\ The LList pointer is used to refer to objects of type\ LLIST, which implement a linked list. The operations on\ these objects are LListNew(), LListLength(), LListEntry(),\ LListAppend(), LListCopy(), and LListFree(). These are\ mostly used internally by the lisp system but are avail-\ able for outside use. Maybe I'll write more documentation\ for them later if it seems necessary. LAKES The Lake structure is a generalization of an input stream.\ It contains three members: an input FILE pointer\ ("streamin"), an output FILE pointer ("streamout"), and an\ arbitrary pointer ("river"). The input FILE pointer is\ required; the lisp interpreter assumes that every lake has\ a valid input file pointer. The output FILE pointer is\ required if you do any operations that result in the\ intepreter producing any output. The third pointer may\ point to whatever you want. The lisp interpreter itself\ does not directly refer to this pointer. It may be used\ by the parser that you supply when defining a new lisp Geometry Center Oct 22 1992 7 [lisp(3)](/lisp/3.md) [lisp(3)](/lisp/3.md) object type. The term "Lake" is supposed to connote something more gen-\ eral than a stream; it also seemed particularly appropri-\ ate since this interpreter was written in the City of\ Lakes. HIDDEN LAKE ARGUMENTS AND OTHER WET THINGS\ This section is X rated. Don't read it unless you are\ really serious. The lisp interpreter works by first parsing (LSexpr()) an\ expression then evaluating it (LEval()). The LDECLARE\ macro is a mechanism which allows both the syntax (for\ parsing) and the semantics (for evaluation) of an expres-\ sion to be specified in the same convenient place --- at\ the top of the C function which implements the function.\ The call syntax of all such C functions is LObject \*func(Lake \*lake, LList \*args) When parsing a call to the corresponding lisp function,\ LSexpr() calls func with that lake pointer, and with args\ pointing to the head of the list in the parse tree corre-\ sponding to this function call. LDECLARE parses the argu-\ ments in the call (by reading them from the lake) and\ appends them to this list. (Note: the head of this list\ is the function itself, so the first argument becomes\ entry #2 in the list.) When evaluating the function call, LEval() calls func with\ lake=NULL and with args pointing to the call's argument\ list. (In this case the first entry of the list is the\ first argument.) LDECLARE then converts the arguments in\ the list into the appropriate C data types, writing their\ values into the addresses in the \s. One side-effect of using lake=NULL as the signal to evalu-\ ate rather than to parse is that the value of the lake\ pointer is not available at evaluation time. Some func-\ tions, however, may want to do something with the lake\ they were parsed from. For example, the "write" function\ in geomview writes data to the output stream associated\ with its input stream. (In geomview these streams are all\ stored in a general "Pool" structure which is retained as\ the "river" member of the lake.) The special token LLAKE\ may be used to cause the lake pointer to be saved in the\ args list at parse time and written into a variable at\ evaluation time. It is used exactly like the other Geometry Center Oct 22 1992 8 [lisp(3)](/lisp/3.md) [lisp(3)](/lisp/3.md) (scalar) argument keywords: LObject \*func(Lake \*lake, LList \*args)\ Lake \*mylake;\ LDECLARE(("myfunc", LBEGIN\ LARG\_LAKE, &mylake,\ ...\ LARG\_END)); At evaluation time LDECLARE will set mylake to have the\ value that lake had at parse time. This looks just like a\ specification for an argument to the lisp function but it\ is not --- it is just a way to tell LDECLARE to remember\ the lake pointer between parse- and evaluation-time. BUGS\ The documentation is incomplete. AUTHOR\ The lisp interpreter was written mostly by Mark Phillips\ with lots of input and moral support from Stuart Levy and\ Tamara Munzner. Geometry Center Oct 22 1992 9