Package and symbol operations
Functions that deal with symbols alone or in the context of packages. Here we just describe the functions in terms of input and output. Further explanation will be in different section.
SYMBOL-VALUE and SYMBOL-FUNCTION
Return the symbol's value resp. function object bound in global context. Both accept one argument that must be symbol.
>(symbol-value 'pi) ; PI is global variable 3.14159 >(symbol-function 'cons) ; CONS is standard function #<function CONS>
SYMBOL-NAME
Expects one argument that must be symbol. Returns the symbol's name as string.
>(symbol-name 'pi) ; PI is global variable "PI"
FIND-SYMBOL
Finds symbol by name in a package. Expects one string argument - the symbol name - and optional argument which is a package designator. Package designator can be string or symbol or package object itself. If the package name is not supplied, dynamic current package is used. Returns the symbol if it is found, otherwise NIL. If it is found, also prints the symbol's relation to the package. As in Common LISP, this function returns two values, the second is a keyword which characterizes the relation.
>(find-symbol "PI") ; USER package will be searched PI :INHERITED ; it is inherited from base package LABLISP >(find-symbol "PI" "LABLISP") ; now we search in LABLISP package PI :EXTERNAL ; there the symbol is external
It is prefered to call the packages by string names, when we explicitly know it. It is also possible to use a symbol, with the name same as the name of the package. But it is important to know that the package is not bound to the symbol.
(find-symbol "PI" 'user) ; USER package will be searched as above :INHERITED
The name of the symbol USER names existing package, but as a byproduct, we created a new symbol USER and interned it in “USER” package. Using symbols as package designators might lead to confussion as to where the symbol is actually interned (see below INTERN)
(find-symbol "PI" *PACKAGE*) ; *PACKAGE* is global variable :INHERITED
Here the symbol *PACKAGE* is evaluated to the dynamic current package. So the last example is identical to call the function without the optional package argument.
MAKE-SYMBOL
Creates new symbol with given name, outside of any package (homeless). Expects one string argument.
>(make-symbol "BLA") #:BLA ; the prefix means that the symbol is homeless
The example above creates the symbol, it is returned, but then it is discrded, because it has no owner and no binding.
INTERN
Like FIND-SYMBOL, looks up symbol by name in a package, and returns it the same way as FIND-SYMBOL. But when it is not present, it makes a new symbol with the package as owner. Expects one string argument - the symbol name - and optional argument which is a package designator. Returns two values, like FIND-SYMBOL.
>(intern "BLA") ; without the package designator give, will use USER package BLA NIL ; NIL means that it is a new symbol >(intern "BLA") ; we can call it again, for USER package BLA :INTERNAL ; now it is already present as internal symbol
SYMBOL-PACKAGE
Expects single argument that must be symbol. Returns the symbol's home package - the package where the symbol was interned.
>(symbol-package 'pi) #<The LABLISP package>
PACKAGE-NAME
Expects single argument that must be package object. Returns the name as string.
>(package-name *package*) "USER"
FIND-PACKAGE
Expects one argument that must be package designator. Package designator can be string or symbol or package object itself. Returns the package object, if it exists.
>(find-package "USER") #<The USER package>
MAKE-PACKAGE
Expects single argument that must be string. Creates and returns new package with that name, unless it already exists - in that case complains and returns NIL. New package always uses the LabLisp base package LABLISP, see below: USE-PACKAGE.
>(make-package "P1") #<The P1 package>
IN-PACKAGE
Expects single argument that must be string. Switches the current package (dynamic variable *PACKAGE*) to the package named by the string - if it exists - and returns the package.
>(in-package "P1") ; assuming we made the P1 package in previous example #<The P1 package>
USE-PACKAGE
UNUSE-PACKAGE
IMPORT
EXPORT
UNINTERN
UNEXPORT
LIST-ALL-PACKAGES
PACKAGE-USE-LIST
PACKAGE-USED-BY-LIST
PACKAGE-INTERNAL-SYMBOLS
PACKAGE-EXTERNAL-SYMBOLS