2. LITATOMS
A "litatom" (for "literal atom") is an object which conceptually consists of a print name, a value, a function definition, and a property list. In some Lisp dialects, litatoms are also known as "symbols."
A litatom is read as any string of non-delimiting characters that cannot be interpreted as a number. The syntatic characters that delimit litatoms are called separator or break characters (see page X.XX) and normally are space, end-of-line, line-feed, ( (left paren), ) (right paren), " (double quote), [ (left bracket), and ] (right bracket). However, any character may be included in a litatom by preceding it with the character %. Here are some examples of litatoms:
A wxyz 23SKIDDOO %] 3.1415+17
Long% Litatom% With% Embedded% Spaces
(LITATOM X) [Function]
Returns T if X is a litatom, NIL otherwise. Note that a number is not a litatom.
(LITATOM NIL) =T.
(ATOM X) [Function]
Returns T if X is an atom (i.e. a litatom or a number); NIL otherwise.
Warning: (ATOM X) is NIL if X is an array, string, etc. In many dialects of Lisp, the function ATOM is defined equivalent to the Interlisp function NLISTP.
(ATOM NIL) = T.
Litatoms are printed by PRINT and PRIN2 as a sequence of characters with %'s inserted before all delimiting characters (so that the litatom will read back in properly). Litatoms are printed by PRIN1 as a sequence of characters without these extra %'s. For example, the litatom consisting of the five characters A, B, C, (, and D will be printed as ABC%(D by PRINT and ABC(D by PRIN1.
Litatoms can also be constructed by PACK, PACK*, SUBATOM, MKATOM, and GENSYM (which uses MKATOM).
Litatoms are unique. In other words, if two litatoms print the same, they will always be EQ. Note that this is not true for strings, large integers, floating point numbers, and lists; they all can print the same without being EQ. Thus if PACK or MKATOM is given a list of characters corresponding to a litatom that already exists, they return a pointer to that litatom, and do not make a new litatom. Similarly, if the read program is given as input a sequence of characters for which a litatom already exists, it returns a pointer to that litatom. Note: Interlisp is different from other Lisp dialects which allow "uninterned" litatoms.
Note: Litatoms are limited to 255 characters in Interlisp-D; 127 characters in Interlisp-10. Attempting to create a larger litatom either via PACK or by typing one in (or reading from a file) will cause an error, ATOM TOO LONG.
2.1 Using Litatoms as Variables
Litatoms are commonly used as variables. Each litatom has a "top level" variable binding, which can be an arbitrary Interlisp object. Litatoms may also be given special variable bindings within PROGs or function calls, which only exist for the duration of the function. When a litatom is evaluated, the "current" variable binding is returned. This is the most recent special variable binding, or the top level binding if the litatom has not been rebound. SETQ is used to change the current binding. For more information on variable bindings in Interlisp, see page X.XX.
Note: The compiler (page X.XX) treats variables somewhat differently than the interpreter, and the user has to be aware of these differences when writing functions that will be compiled. For example, variable references in compiled code are not checked for NOBIND, so compiled code will not generate unbound atom errors. In general, it is better to debug interpreted code, before compiling it for speed. The compiler offers some facilities to increase the efficiency of variable use in compiled functions. Global variables (page X.XX) can be defined so that the entire stack is not searched at each variable reference. Local variables (page X.XX) allow compiled functions to access variable bindings which are not on the stack, which reduces variable conflicts, and also makes variable lookup faster.
By convention, a litatom whose top level binding is to the litatom NOBIND is considered to have no top level binding. If a litatom has no local variable bindings, and its top level value is NOBIND, attempting to evaluate it will cause an unbound atom error.
The two litatoms T and NIL always evaluate to themselves. Attempting to change the binding of T or NIL with the functions below will generate the error ATTEMPT TO SET T or ATTEMPT TO SET NIL.
The following functions (except BOUNDP) will also generate the error ARG NOT LITATOM, if not given a litatom.
(BOUNDP VAR) [Function]
Returns T if VAR has a special variable binding (even if bound to NOBIND), or if VAR has a top level value other than NOBIND; otherwise NIL. In other words, if X is a litatom, (EVAL X) will cause an UNBOUND ATOM error if and only if (BOUNDP X) returns NIL.
(SET VAR VALUE) [Function]
Sets the "current" variable binding of VAR to VALUE, and returns VALUE.
Note that SET is a normal lambda spread function, so both VAR and VALUE are evaluated before it is called. Thus, if the value of X is B, and the value of Y is C, then (SET X Y) would result in B being set to C, and C being returned as the value of SET.
(SETQ VAR VALUE) [NLambda NoSpread Function]
Nlambda version of SET; VAR is not evaluated, VALUE is. Thus if the value of X is B and the value of Y is C, (SETQ X Y) would result in X (not B) being set to C, and C being returned.
Note: Since SETQ is an nlambda, neither argument is evaluated during the calling process. However, SETQ itself calls EVAL on its second argument. As a result, typing (SETQ VAR FORM) and SETQ(VAR FORM) to the Interlisp executive is equivalent: in both cases VAR is not evaluated, and FORM is.
(SETQQ VAR VALUE) [NLambda Function]
Like SETQ except that neither argument is evaluated, e.g., (SETQQ X (A B C)) sets X to (A B C).
(PSETQ VAR1 VALUE1 ... VARN VALUEN) [Macro]
Does a multiple SETQ of VAR1 (unevaluated) to the value of VALUE1, VAR2 to the value of VALUE2, etc. All of the VALUEi terms are evaluated before any of the assignments. Therefore, (PSETQ A B B A) can be used to swap the values of the variables A and B.
(GETTOPVAL VAR) [Function]
Returns the top level value of VAR (even if NOBIND), regardless of any intervening local bindings.
(SETTOPVAL VAR VALUE) [Function]
Sets the top level value of VAR to VALUE, regardless of any intervening bindings, and returns VALUE.
A major difference between various Interlisp implementations is the way that variable bindings are implemented. Interlisp-10 and Interlisp-Jerico use what is called "shallow" binding. Interlisp-D and Interlisp-VAX use what is called "deep" binding.
In a deep binding system, a variable is bound by saving on the stack the variable's new value. When a variable is accessed, its value is found by searching the stack for the most recent binding. If the variable is not found on the stack, the top level binding is retrieved from a "value cell" associated with the variable.
In a "shallow" binding system, a variable is bound by saving on the stack the variable name and the variable's old value and putting the new value in the variable's value cell. When a variable is accessed, its value is always found in its value cell.
GETTOPVAL and SETTOPVAL are less efficient in a shallow binding system, because they have to search the stack for rebindings; it is more economical to simply rebind variables. In a deep binding system, GETTOPVAL and SETTOPVAL are very efficient since they do not have to search the stack, but can simply access the value cell directly.
GETATOMVAL and SETATOMVAL can be used to access a variable's value cell, in either a shallow or deep binding system.
(GETATOMVAL VAR) [Function]
Returns the value in the value cell of VAR. In a shallow binding system, this is the same as (EVAL ATM), or simply VAR. In a deep binding system, this is the same as (GETTOPVAL VAR).
(SETATOMVAL VAR VALUE) [Function]
Sets the value cell of VAR to VALUE. In a shallow binding system, this is the same as SET; in a deep binding system, this is the same as SETTOPVAL.
2.2 Function Definition Cells
Each litatom has a function definition cell, which is accessed when a litatom is used as a function. The mechanism for accessing and setting the function definition cell of a litatom is described on page X.XX.
2.3 Property Lists
Each litatom has an associated property list, which allows a set of named objects to be associated with the litatom. A property list associates a name, known as a "property name" or "property", with an abitrary object, the "property value" or simply "value". Sometimes the phrase "to store on the property X" is used, meaning to place the indicated information on a property list under the property name X.
Property names are usually litatoms or numbers, although no checks are made. However, the standard property list functions all use EQ to search for property names, so they may not work with non-atomic property names. Note that the same object can be used as both a property name and a property value.
Note: Many litatoms in the system already have property lists, with properties used by the compiler, the break package, DWIM, etc. Be careful not to clobber such system properties. The variable SYSPROPS is a list of property names used by the system.
The functions below are used to manipulate the propert lists of litatoms. Except when indicated, they generate the error ARG NOT LITATOM, if given an object that is not a litatom.
(GETPROP ATM PROP) [Function]
Returns the property value for PROP from the property list of ATM. Returns NIL if ATM is not a litatom, or PROP is not found. Note that GETPROP also returns NIL if there is an occurrence of PROP but the corresponding property value is NIL; this can be a source of program errors.
Note: GETPROP used to be called GETP.
(PUTPROP ATM PROP VAL) [Function]
Puts the property PROP with value VAL on the property list of ATM. VAL replaces any previous value for the property PROP on this property list. Returns VAL.
(ADDPROP ATM PROP NEW FLG) [Function]
Adds the value NEW to the list which is the value of property PROP on the property list of ATM. If FLG is T, NEW is CONSed onto the front of the property value of PROP, otherwise it is NCONCed on the end (using NCONC1). If ATM does not have a property PROP, or the value is not a list, then the effect is the same as (PUTPROP ATM PROP (LIST NEW)). ADDPROP returns the (new) property value. Example:
← (PUTPROP 'POCKET 'CONTENTS NIL)
NIL
← (ADDPROP 'POCKET 'CONTENTS 'COMB)
(COMB)
← (ADDPROP 'POCKET 'CONTENTS 'WALLET)
(COMB WALLET)
(REMPROP ATM PROP) [Function]
Removes all occurrences of the property PROP (and its value) from the property list of ATM. Returns PROP if any were found, otherwise NIL.
(REMPROPLIST ATM PROPS) [Function]
Removes all occurrences of all properties on the list PROPS (and their corresponding property values) from the property list of ATM. Returns NIL.
(CHANGEPROP X PROP1 PROP2) [Function]
Changes the property name of property PROP1 to PROP2 on the property list of X, (but does not affect the value of the property). Returns X, unless PROP1 is not found, in which case it returns NIL.
(PROPNAMES ATM) [Function]
Returns a list of the property names on the property list of ATM.
(DEFLIST L PROP) [Function]
Used to put values under the same property name on the property lists of several litatoms. L is a list of two-element lists. The first element of each is a litatom, and the second element is the property value for the property PROP. Returns NIL. For example,
(DEFLIST '( (FOO MA) (BAR CA) (BAZ RI) ) 'STATE)
puts MA on FOO's STATE property, CA on BAR's STATE property, and RI on BAZ's STATE property.
Property lists are conventionally implemented as lists of the form
(NAME1 VALUE1 NAME2 VALUE2 ...)
although the user can store anything as the property list of a litatom. However, the functions which manipulate property lists observe this convention by searching down the property lists two CDRs at a time. Most of these functions also generate an error, ARG NOT LITATOM, if given an argument which is not a litatom, so they cannot be used directly on lists. (LISTPUT, LISTPUT1, LISTGET, and LISTGET1 are functions similar to PUTPROP and GETPROP that work directly on lists. See page X.XX.) The property lists of litatoms can be directly accessed with the following functions:
(GETPROPLIST ATM) [Function]
Returns the property list of ATM.
(SETPROPLIST ATM LST) [Function]
If ATM is a litatom, sets the property list of ATM to be LST, and returns LST as its value.
(GETLIS X PROPS) [Function]
Searches the property list of X, and returns the property list as of the first property on PROPS that it finds. For example,
← (GETPROPLIST 'X)
(PROP1 A PROP3 B A C)
← (GETLIS 'X '(PROP2 PROP3))
(PROP3 B A C)
Returns NIL if no element on PROPS is found. X can also be a list itself, in which case it is searched as described above. If X is not a litatom or a list, returns NIL.
2.4 Print Names
Each litatom has a print name, a string of characters that uniquely identifies that litatom. The term "print name" has been extended, however, to refer to the characters that are output when any object is printed. In Interlisp, all objects have print names, although only litatoms and strings have their print name explicitly stored. This section describes a set of functions which can be used to access and manipulate the print names of any object, though they are primarily used with the print names of litatoms.
The print name of an object is those characters that are output when the object is printed using PRIN1, e.g., the print name of the litatom ABC%(D consists of the five characters ABC(D. The print name of the list (A B C) consists of the seven characters (A B C) (two of the characters are spaces).
Sometimes we will have occasion to refer to a "PRIN2-name." The PRIN2-name of an object is those characters output when the object is printed using PRIN2. Thus the PRIN2-name of the litatom ABC%(D is the six characters ABC%(D. Note that the PRIN2-name depends on what readtable is being used (see page X.XX), since this determines where %'s will be inserted. Many of the functions below allow either print names or PRIN2-names to be used, as specified by FLG and RDTBL arguments. If FLG is NIL, print names are used. Otherwise, PRIN2-names are used, computed with respect to the readtable RDTBL (or the current readtable, if RDTBL = NIL).
Note: The print name of an integer depends on the setting of RADIX (page X.XX). The functions described in this section (UNPACK, NCHARS, etc.) define the print name of an integer as though the radix was 10, so that (PACK (UNPACK 'X9)) will always be X9 (and not X11, if RADIX is set to 8). However, integers will still be printed by PRIN1 using the current radix. The user can force these functions to use print names in the current radix by changing the setting of the variable PRXFLG (page X.XX).
(MKATOM X) [Function]
Creates and returns an atom whose print name is the same as that of the string X or, if X isn't a string, the same as that of (MKSTRING X). Examples:
(MKATOM '(A B C)) => %(A% B% C%)
(MKATOM "1.5") => 1.5
Note that the last example returns a number, not a litatom. It is a deeply-ingrained feature of Interlisp that no litatom can have the print name of a number.
(SUBATOM X N M) [Function]
Equivalent to (MKATOM (SUBSTRING X N M)), but does not make a string pointer (see page X.XX). Returns an atom made from the Nth through Mth characters of the print name of X. If N or M are negative, they specify positions counting backwards from the end of the print name. Examples:
(SUBATOM "FOO1.5BAR" 4 6) => 1.5
(SUBATOM '(A B C) 2 -2) => A% B% C
(PACK X) [Function]
If X is a list of atoms, PACK returns a single atom whose print name is the concatenation of the print names of the atoms in X. If the concatenated print name is the same as that of a number, PACK will return that number. For example,
(PACK '(A BC DEF G)) => ABCDEFG
(PACK '(1 3.4)) => 13.4
(PACK '(1 E -2)) => .01
Although X is usually a list of atoms, it can be a list of arbitrary Interlisp objects. The value of PACK is still a single atom whose print name is the concatenation of the print names of all the elements of X, e.g.,
(PACK '((A B) "CD")) => %(A% B%)CD
If X is not a list or NIL, PACK generates an error, ILLEGAL ARG.
(PACK* X1 X2 ... XN) [NoSpread Function]
Nospread version of PACK that takes an arbitrary number of arguments, instead of a list. Examples:,
(PACK* 'A 'BC 'DEF 'G) => ABCDEFG
(PACK* 1 3.4) => 13.4
(UNPACK X FLG RDTBL) [Function]
Returns the print name of X as a list of single-characters atoms, e.g.,
(UNPACK 'ABC5D) => (A B C 5 D)
(UNPACK "ABC(D") => (A B C %( D)
If FLG=T, the PRIN2-name of X is used (computed with respect to RDTBL), e.g.,
(UNPACK "ABC(D" T) => (%" A B C %( D %")
(UNPACK 'ABC%(D" T) => (A B C %% %( D)
Note: (UNPACK X) performs N CONSes, where N is the number of characters in the print name of X.
(DUNPACK X SCRATCHLIST FLG RDTBL) [Function]
A destructive version of UNPACK that does not perform any CONSes but instead reuses the list SCRATCHLIST. If the print name is too long to fit in SCRATCHLIST, DUNPACK will extend it. If SCRATCHLIST is not a list, DUNPACK returns (UNPACK X FLG RDTBL).
(NCHARS X FLG RDTBL) [Function]
Returns the number of characters in the print name of X. If FLG=T, the PRIN2-name is used. For example,
(NCHARS 'ABC) => 3
(NCHARS "ABC" T) => 5
Note: NCHARS works most efficiently on litatoms and strings, but can be given any object.
(NTHCHAR X N FLG RDTBL) [Function]
Returns the Nth character of the print name of X as an atom. N can be negative, in which case it counts from the end of the print name, e.g., -1 refers to the last character, -2 next to last, etc. If N is greater than the number of characters in the print name, or less than minus that number, or 0, NTHCHAR returns NIL. Examples:
(NTHCHAR 'ABC 2) => B
(NTHCHAR 15.6 2) => 5
(NTHCHAR 'ABC%(D -3 T) => %%
(NTHCHAR "ABC" 2) => B
(NTHCHAR "ABC" 2 T) => A
Note: NTHCHAR and NCHARS work much faster on objects that actually have an internal representation of their print name, i.e., litatoms and strings, than they do on numbers and lists, as they do not have to simulate printing.
(L-CASE X FLG) [Function]
Returns a lower case version of X. If FLG is T, the first letter is capitalized. If X is a string, the value of L-CASE is also a string. If X is a list, L-CASE returns a new list in which L-CASE is computed for each corresponding element and non-NIL tail of the original list. Examples:
(L-CASE 'FOO) => foo
(L-CASE 'FOO T) => Foo
(L-CASE "FILE NOT FOUND" T) => "File not found"
(L-CASE '(JANUARY FEBRUARY (MARCH "APRIL")) T)
=> '(January February (March "April"))
(U-CASE X) [Function]
Similar to L-CASE, except returns the upper case version of X.
(U-CASEP X) [Function]
Returns T if X contains no lower case letters; NIL otherwise.
(GENSYM PREFIX ) [Function]
Returns a litatom of the form Xnnnn, where X=PREFIX (or A if PREFIX is NIL) and nnnn is an integer. Thus, the first one generated is A0001, the second A0002, etc. The integer suffix is always at least four characters long, but it can grow beyond that. For example, the next litatom produced after A9999 would be A10000. GENSYM provides a way of generating litatoms for various uses within the system.
GENNUM [Variable]
The value of GENNUM, initially 0, determines the next GENSYM, e.g., if GENNUM is set to 23, (GENSYM)=A0024.
The term "gensym" is used to indicate a litatom that was produced by the function GENSYM. Litatoms generated by GENSYM are the same as any other litatoms: they have property lists, and can be given function definitions. Note that the litatoms are not guaranteed to be new. For example, if the user has previously created A0012, either by typing it in, or via PACK or GENSYM itself, then if GENNUM is set to 11, the next litatom returned by GENSYM will be the A0012 already in existence.
(MAPATOMS FN) [Function]
Applies FN (a function or lambda expression) to every litatom in the system. Returns NIL
For example,
(MAPATOMS (FUNCTION (LAMBDA(X)
(if (GETD X) then (PRINT X)]
will print every litatom with a function definition.
Note: In some implementations of Interlisp, unused litatoms may be garbage collected, which can effect the action of MAPATOMS.
(APROPOS STRING ALLFLG QUIETFLG OUTPUT) [Function]
APROPOS scans all litatoms in the system for those which have STRING as a substring and prints them on the terminal along with a line for each relevant item defined for each selected atom. Relevant items are (1) function definitions, for which only the arglist is printed, (2) dynamic variable values, and (3) non-null property lists. PRINTLEVEL (page X.XX) is set to (3 . 5) when APROPOS is printing.
If ALLFLG is NIL, then atoms with no relevant items and "internal" atoms are omitted ("internal" currently means those litatoms whose print name begins with a \ or those litatoms produced by GENSYM). If ALLFLG is a function (i.e., (FNTYP ALLFLG) is non-NIL), then it is used as a predicate on atoms selected by the substring match, with value NIL meaning to omit the atom. If ALLFLG is any other non-NIL value, then no atoms are omitted.
If QUIETFLG is non-NIL, then no printing at all is done, but instead a list of the selected atoms is returned.
If OUTPUT is non-NIL, the printing will be directed to OUTPUT (which should be a stream open for output) instead of to the terminal stream.
2.5 Characters and Character Codes
Characters may be represented in two ways: as single-character atoms, or as integer character codes. In many situations, it is more efficient to use character codes, so Interlisp provides parallel functions for both representations.
Interlisp-D uses the 16-bit NS character set, described in the document Character Code Standard [Xerox System Integration Standards, XSIS 058404, April 1984]. Legal character codes range from 0 to 65535. The NS (Network Systems) character encoding encompasses a much wider set of available characters than the 8-bit character standards (such as ASCII), including characters comprising many foreign alphabets and special symbols. For instance, Interlisp-D supports the display and printing of the following:
Le syst me d'information Xerox 11xx est remarquablement polyglotte.
Das Xerox 11xx Kommunikationssystem bietet merkw rdige multilinguale Nutzm glichkeiten.
M [w] v with Rwv: M [v]
These characters can be used in strings, litatom print names, symbolic files, or anywhere else 8-bit characters could be used. All of the standard string and print name functions (RPLSTRING, GNC, NCHARS, STRPOS, etc.) accept litatoms and strings containing NS characters. For example:
←(STRPOS "char" "this is an 8-bit character string")
18
←(STRPOS "char" "celui-ci comporte des charact res NS")
23
In almost all cases, a program does not have to distinguish between NS characters or 8-bit characters. The exception to this rule is the handling of input/output operations (see page X.XX).
The function CHARCODE (page X.XX) provides a simple way to create individual NS characters codes. The VirtualKeyboards library package provides a set of virtual keyboards that allow keyboard or mouse entry of NS characters.
(PACKC X) [Function]
Similar to PACK except X is a list of character codes. For example,
(PACKC '(70 79 79)) => FOO
(CHCON X FLG RDTBL) [Function]
Like UNPACK, except returns the print name of X as a list of character codes. If FLG=T, the PRIN2-name is used. For example,
(CHCON 'FOO) => (70 79 79)
(DCHCON X SCRATCHLIST FLG RDTBL) [Function]
Similar to DUNPACK.
(NTHCHARCODE X N FLG RDTBL) [Function]
Similar to NTHCHAR, except returns the character code of the Nth character of the print name of X. If N is negative, it is interpreted as a count backwards from the end of X. If the absolute value of N is greater than the number of characters in X, or 0, then the value of NTHCHARCODE is NIL.
If FLG is T, then the PRIN2-name of X is used, computed with respect to the readtable RDTBL
(CHCON1 X) [Function]
Returns the character code of the first character of the print name of X; equal to (NTHCHARCODE X 1).
(CHARACTER N) [Function]
N is a character code. Returns the atom having the corresponding single character as its print name.
(CHARACTER 70) => F
(FCHARACTER N) [Function]
Fast version of CHARACTER that compiles open.
The following function makes it possible to gain the efficiency that comes from dealing with character codes without losing the symbolic advantages of character atoms:
(CHARCODE CHAR) [NLambda Function]
Returns the character code specified by CHAR (unevaluated). If CHAR is a one-character atom or string, the corresponding character code is simply returned. Thus, (CHARCODE A) is 65, (CHARCODE 0) is 48. If CHAR is a multi-character litatom or string, it specifies a character code as described below. If CHAR is NIL, CHARCODE simply returns NIL. Finally, if CHAR is a list structure, the value is a copy of CHAR with all the leaves replaced by the corresponding character codes. For instance, (CHARCODE (A (B C))) => (65 (66 67)).
If a character is specified by a multi-character litatom or string, CHARCODE interprets it as follows:
CR, SPACE, etc. The variable CHARACTERNAMES contains an association list mapping special litatoms to character codes. Among the characters defined this way are CR (13), LF (10), SPACE or SP (32), ESCAPE or ESC (27), BELL (7), BS (8), TAB (9), NULL (0), and DEL (127). The litatom EOL maps into the appropriate End-Of-Line character code in the different Interlisp implementations (31 in Interlisp-10, 13 in Interlisp-D, 10 in Interlisp-VAX). Examples:
(CHARCODE SPACE) => 32
(CHARCODE CR) => 13
CHARSET,CHARNUM
CHARSET-CHARNUM If the character specification is a litatom or string of the form CHARSET,CHARNUM or CHARSET-CHARNUM, the character code for the character number CHARNUM in the character set CHARSET is returned.
The 16-bit NS character encoding is divided into a large number of "character sets." Each 16-bit character can be decoded into a character set (an integer from 0 to 254 inclusive) and a character number (also an integer from 0 to 254 inclusive). CHARSET is either an octal number, or a litatom in the association list CHARACTERSETNAMES (which defines the character sets for GREEK, CYRILLIC, etc.).
CHARNUM is either an octal number, a single-character litatom, or a litatom from the association list CHARACTERNAMES. Note that if CHARNUM is a single-digit number, it is interpreted as the character "2", rather than as the octal number 2. Examples:
(CHARCODE 12,6) => 2566
(CHARCODE 12,SPACE) => 2592
(CHARCODE GREEK,A) => 9793
↑CHARSPEC (control chars) If the character specification is a litatom or string of one of the forms above, preceeded by the character "↑", this indicates a "control character," derived from the normal character code by clearing the seventh bit of the character code (normally set). Examples:
(CHARCODE ↑A) => 1
(CHARCODE ↑GREEK,A) => 9729
#CHARSPEC (meta chars) If the character specification is a litatom or string of one of the forms above, preceeded by the character "#", this indicates a "meta character," derived from the normal character code by setting the eighth bit of the character code (normally cleared). ↑ and # can both be set at once. Examples:
(CHARCODE #A) => 193
(CHARCODE #↑GREEK,A) => 9857
A CHARCODE form can be used wherever a structure of character codes would be appropriate. For example:
(FMEMB (NTHCHARCODE X 1) (CHARCODE (CR LF SPACE ↑A)))
(EQ (READCCODE FOO) (CHARCODE GREEK,A))
There is a macro for CHARCODE which causes the character-code structure to be constructed at compile-time. Thus, the compiled code for these examples is exactly as efficient as the less readable:
(FMEMB (NTHCHARCODE X 1) (QUOTE (13 10 32 1)))
(EQ (READCCODE FOO) 9793)
(SELCHARQ E CLAUSE1 ... CLAUSEN DEFAULT) [Macro]
Similar to SELECTQ (page X.XX), except that the selection keys are determined by applying CHARCODE (instead of QUOTE) to the key-expressions. If the value of E is a character code or NIL and it is EQ or MEMB to the result of applying CHARCODE to the first element of a clause, the remaining forms of that clause are evaluated. Otherwise, the default is evaluated.
Thus
(SELCHARQ (BIN FOO)
((SPACE TAB) (FUM))
((↑D NIL) (BAR))
(a (BAZ))
(ZIP))
is exactly equivalent to
(SELECTQ (BIN FOO)
((32 9) (FUM))
((4 NIL) (BAR))
(97 (BAZ))
(ZIP))
Furthermore, SELCHARQ has a macro definition such that it always compiles as an equivalent SELECTQ.
Copyright (c) 1985 Xerox Corporation. All rights reserved.