{ $description "Outputs an array containing a copy of the data stack contents right before the call to this word, with the top of the stack at the end of the array." } ;
HELP:set-datastack( ds-- )
{ $values { "ds"array } }
{ $description "Replaces the data stack contents with a copy of an array. The end of the array becomes the top of the stack." } ;
HELP:retainstack( -- rs)
{ $values { "rs"array } }
{ $description "Outputs an array containing a copy of the retain stack contents right before the call to this word, with the top of the stack at the end of the array." } ;
HELP:set-retainstack( rs-- )
{ $values { "rs"array } }
{ $description "Replaces the retain stack contents with a copy of an array. The end of the array becomes the top of the stack." } ;
HELP:callstack( -- cs)
{ $values { "cs"callstack } }
{ $description "Outputs a copy of the call stack contents, with the top of the stack at the end of the vector. The stack frame of the caller word is " { $emphasis "not" } " included." } ;
{ "If two objects are equal under " { $link = } ", they must have equal hashcodes." }
{ "If the hashcode of an object depends on the values of its slots, the hashcode of the slots must be computed recursively by calling " { $link hashcode* } " with a " { $snippet "level" } " parameter decremented by one. This avoids excessive work while still computing well-distributed hashcodes. The " { $link recursive-hashcode } " combinator can help with implementing this logic," }
{ "The hashcode should be a " { $link fixnum } ", however returning a " { $link bignum } " will not cause any problems other than potential performance degradation." }
{ "The hashcode is only permitted to change between two invocations if the object or one of its slot values was mutated." }
"If mutable objects are used as hashtable keys, they must not be mutated in such a way that their hashcode changes. Doing so will violate bucket sorting invariants and result in undefined behavior. See " { $link "hashtables.keys" } " for details." } ;
{ $description "Outputs the identity hashcode of an object. The identity hashcode is not guaranteed to be unique, however it will not change during the object's lifetime." } ;
"Tests if two objects are equal. If " { $snippet "obj1" } " and " { $snippet "obj2" } " point to the same object, outputs " { $link t } ". Otherwise, calls the " { $link equal? } " generic word."
"User code should call " { $link = } " instead; that word first tests the case where the objects are " { $link eq? } ", and so by extension, methods defined on " { $link equal? } " assume they are never called on " { $link eq? } " objects."
$nl
"Method definitions should ensure that this is an equality relation, modulo the assumption that the two objects are not " { $link eq? } ". That is, for any three non-" { $link eq? } " objects " { $snippet "a" } ", " { $snippet "b" } " and " { $snippet "c" } ", we must have:"
"To define a tuple class such that two instances are only equal if they are both the same instance, inherit from the " { $link identity-tuple } " class. This class defines a method on " { $link equal? } " which always returns " { $link f } ". Since " { $link = } " handles the case where the two objects are " { $link eq? } ", this method will never be called with two " { $link eq? } " objects, so such a definition is valid:"
{ $contract "Outputs a new object equal to the given object. This is not guaranteed to actually copy the object; it does nothing with immutable objects, and does not copy words either. However, sequences and tuples can be cloned to obtain a shallow copy of the original." } ;
{ $description "Convert a generalized boolean into a boolean. That is, " { $link f } " retains its value, whereas anything else becomes " { $link t } "." } ;
{ $description "For " { $link f } " outputs " { $link t } " and for anything else outputs " { $link f } "." }
{ $notes "This word implements boolean not, so applying it to integers will not yield useful results (all integers have a true value). Bitwise not is the " { $link bitnot } " word." } ;
{ $description "If both inputs are true, outputs " { $snippet "obj2" } ". otherwise outputs " { $link f } "." }
{ $notes "This word implements boolean and, so applying it to integers will not yield useful results (all integers have a true value). Bitwise and is the " { $link bitand } " word." }
{ $examples
"Usually only the boolean value of the result is used, however you can also explicitly rely on the behavior that if both inputs are true, the second is output:"
{ $description "If both inputs are false, outputs " { $link f } ". otherwise outputs the first of " { $snippet "obj1" } " and " { $snippet "obj2" } " which is true." }
{ $notes "This word implements boolean inclusive or, so applying it to integers will not yield useful results (all integers have a true value). Bitwise inclusive or is the " { $link bitor } " word." }
{ $examples
"Usually only the boolean value of the result is used, however you can also explicitly rely on the behavior that the result will be the first true input:"
{ $notes "This word implements boolean exclusive or, so applying it to integers will not yield useful results (all integers have a true value). Bitwise exclusive or is the " { $link bitxor } " word." } ;
{ $description "Executes a word. Words which " { $link execute } " an input parameter must be declared " { $link POSTPONE:inline } " so that a caller which passes in a literal word can have a static stack effect." }
{ $description "Executes a word without checking if it is a word first." }
{ $warning "This word is in the " { $vocab-link "kernel.private" } " vocabulary because it is unsafe. Calling with a parameter that is not a word will crash Factor. Use " { $link execute } " instead." } ;
{ $description "Calls a quotation. Words which " { $link call } " an input parameter must be declared " { $link POSTPONE:inline } " so that a caller which passes in a literal quotation can have a static stack effect." }
{ $description "Applies " { $snippet "p" } " to " { $snippet "x" } ", then applies " { $snippet "q" } " to " { $snippet "x" } "." }
{ $examples
"If " { $snippet "[ p ]" } " and " { $snippet "[ q ]" } " have stack effect " { $snippet "( x -- )" } ", then the following two lines are equivalent:"
{ $code
"[ p ] [ q ] bi"
"dup p q"
}
"If " { $snippet "[ p ]" } " and " { $snippet "[ q ]" } " have stack effect " { $snippet "( x -- y )" } ", then the following two lines are equivalent:"
{ $code
"[ p ] [ q ] bi"
"dup p swap q"
}
"In general, the following two lines are equivalent:"
{ $description "Applies " { $snippet "p" } " to the two input values, then applies " { $snippet "q" } " to the two input values." }
{ $examples
"If " { $snippet "[ p ]" } " and " { $snippet "[ q ]" } " have stack effect " { $snippet "( x y -- )" } ", then the following two lines are equivalent:"
{ $code
"[ p ] [ q ] 2bi"
"2dup p q"
}
"If " { $snippet "[ p ]" } " and " { $snippet "[ q ]" } " have stack effect " { $snippet "( x y -- z )" } ", then the following two lines are equivalent:"
"If " { $snippet "[ p ]" } " and " { $snippet "[ q ]" } " have stack effect " { $snippet "( x y z -- )" } ", then the following two lines are equivalent:"
{ $code
"[ p ] [ q ] 3bi"
"3dup p q"
}
"In general, the following two lines are equivalent:"
{ $description "Applies " { $snippet "p" } " to " { $snippet "x" } ", then applies " { $snippet "q" } " to " { $snippet "x" } ", and finally applies " { $snippet "r" } " to " { $snippet "x" } "." }
{ $examples
"If " { $snippet "[ p ]" } ", " { $snippet "[ q ]" } " and " { $snippet "[ r ]" } " have stack effect " { $snippet "( x -- )" } ", then the following two lines are equivalent:"
{ $code
"[ p ] [ q ] [ r ] tri"
"dup p dup q r"
}
"If " { $snippet "[ p ]" } ", " { $snippet "[ q ]" } " and " { $snippet "[ r ]" } " have stack effect " { $snippet "( x -- y )" } ", then the following two lines are equivalent:"
{ $code
"[ p ] [ q ] [ r ] tri"
"dup p over q rot r"
}
"In general, the following two lines are equivalent:"
{ $description "Applies " { $snippet "p" } " to the two input values, then applies " { $snippet "q" } " to the two input values, and finally applies " { $snippet "r" } " to the two input values." }
{ $examples
"If " { $snippet "[ p ]" } ", " { $snippet "[ q ]" } " and " { $snippet "[ r ]" } " have stack effect " { $snippet "( x y -- )" } ", then the following two lines are equivalent:"
{ $code
"[ p ] [ q ] [ r ] 2tri"
"2dup p 2dup q r"
}
"In general, the following two lines are equivalent:"
{ $description "Applies " { $snippet "p" } " to the three input values, then applies " { $snippet "q" } " to the three input values, and finally applies " { $snippet "r" } " to the three input values." }
{ $examples
"If " { $snippet "[ p ]" } ", " { $snippet "[ q ]" } " and " { $snippet "[ r ]" } " have stack effect " { $snippet "( x y z -- )" } ", then the following two lines are equivalent:"
{ $code
"[ p ] [ q ] [ r ] 3tri"
"3dup p 3dup q r"
}
"In general, the following two lines are equivalent:"
{ $description "Applies the quotation to " { $snippet "u" } " and " { $snippet "v" } ", then to " { $snippet "w" } " and " { $snippet "x" } ", and then to " { $snippet "y" } " and " { $snippet "z" } "." }
"Higher-arity variants of " { $link bi } " can be built from " { $link bi-curry } ":"
{ $code
"[ p ] [ q ] bi-curry bi == [ p ] [ q ] 2bi"
"[ p ] [ q ] bi-curry bi-curry bi == [ p ] [ q ] 3bi"
}
"The combination " { $snippet "bi-curry bi*" } " cannot be expressed with the non-currying dataflow combinators alone; it is equivalent to a stack shuffle preceding " { $link 2bi* } ":"
{ $code
"[ p ] [ q ] bi-curry bi*"
"[ swap ] keep [ p ] [ q ] 2bi*"
}
"To put it another way, " { $snippet "bi-curry bi*" } " handles the case where you have three values " { $snippet "a b c" } " on the stack, and you wish to apply " { $snippet "p" } " to " { $snippet "a c" } " and " { $snippet "q" } " to " { $snippet "b c" } "."
"Higher-arity variants of " { $link tri } " can be built from " { $link tri-curry } ":"
{ $code
"[ p ] [ q ] [ r ] tri-curry tri == [ p ] [ q ] [ r ] 2tri"
"[ p ] [ q ] [ r ] tri-curry tri-curry bi == [ p ] [ q ] [ r ] 3tri"
}
"The combination " { $snippet "tri-curry tri*" } " cannot be expressed with the non-currying dataflow combinators alone; it handles the case where you have four values " { $snippet "a b c d" } " on the stack, and you wish to apply " { $snippet "p" } " to " { $snippet "a d" } ", " { $snippet "q" } " to " { $snippet "b d" } " and " { $snippet "r" } " to " { $snippet "c d" } "." } ;
"The combination " { $snippet "bi-curry* bi" } " is equivalent to a stack shuffle preceding " { $link 2bi* } ":"
{ $code
"[ p ] [ q ] bi-curry* bi"
"[ over ] dip [ p ] [ q ] 2bi*"
}
"In other words, " { $snippet "bi-curry* bi" } " handles the case where you have the three values " { $snippet "a b c" } " on the stack, and you wish to apply " { $snippet "p" } " to " { $snippet "a b" } " and " { $snippet "q" } " to " { $snippet "a c" } "."
$nl
"The combination " { $snippet "bi-curry* bi*" } " is equivalent to a stack shuffle preceding " { $link 2bi* } ":"
{ $code
"[ p ] [ q ] bi-curry* bi*"
"[ swap ] dip [ p ] [ q ] 2bi*"
}
"In other words, " { $snippet "bi-curry* bi*" } " handles the case where you have the four values " { $snippet "a b c d" } " on the stack, and you wish to apply " { $snippet "p" } " to " { $snippet "a c" } " and " { $snippet "q" } " to " { $snippet "b d" } "."
{ $description "Alternative conditional form that preserves the " { $snippet "cond" } " value if it is true."
$nl
"If the condition is true, it is retained on the stack before the " { $snippet "true" } " quotation is called. Otherwise, the condition is removed from the stack and the " { $snippet "false" } " quotation is called."
$nl
"The following two lines are equivalent:"
{ $code "X [ Y ] [ Z ] if*""X dup [ Y ] [ drop Z ] if" } } ;
{ $description "If the condition is " { $link f } ", the " { $snippet "false" } " quotation is called with the " { $snippet "default" } " value on the stack. Otherwise, the " { $snippet "true" } " quotation is called with the condition on the stack." }
{ $notes
"The following two lines are equivalent:"
{ $code "[ X ] [ Y ] ?if""dup [ nip X ] [ drop Y ] if" }
{ $description "Starts the front-end processor (FEP), which is a low-level debugger which can inspect memory addresses and the like. The FEP is also entered when a critical error occurs." }
{ $notes
"The term FEP originates from the Lisp machines of old. According to the Jargon File,"
$nl
{ $strong "fepped out" } " /fept owt/ " { $emphasis "adj." } " The Symbolics 3600 LISP Machine has a Front-End Processor called a `FEP' (compare sense 2 of box). When the main processor gets wedged, the FEP takes control of the keyboard and screen. Such a machine is said to have `fepped out' or `dropped into the fep'."
{ $description "Outputs a byte-by-byte copy of the given object. User code should call " { $link clone } " instead." } ;
HELP:declare
{ $values { "spec""an array of class words" } }
{ $description "Declares that the elements at the top of the stack are instances of the classes in " { $snippet "spec" } "." }
{ $warning "The compiler blindly trusts declarations, and false declarations can lead to crashes, memory corruption and other undesirable behavior." }
{ $examples
"The optimizer cannot do anything with the below code:"
{ $code "2 + 10 *" }
"However, if we declare that the top of the stack is a " { $link float } ", then type checks and generic dispatch are eliminated, and the compiler can use unsafe intrinsics:"
{ $description "Outputs an object's tag number, between zero and one less than " { $link num-types } ". This is implementation detail and user code should call " { $link class } " instead." } ;
{ $description "Reads an object from the Factor VM's environment table. User code never has to read the environment table directly; instead, use one of the callers of this word." } ;
{ $description "Writes an object to the Factor VM's environment table. User code never has to write to the environment table directly; instead, use one of the callers of this word." } ;
HELP:object
{ $class-description
"The class of all objects. If a generic word defines a method specializing on this class, the method is used as a fallback, if no other applicable method is found. For instance:"
{ $description "Partial application. Outputs a " { $link callable } " which first pushes " { $snippet "obj" } " and then calls " { $snippet "quot" } "." }
{ $class-description "The class of objects created by " { $link curry } ". These objects print identically to quotations and implement the sequence protocol, however they only use two cells of storage; a reference to the object and a reference to the underlying quotation." }
{ $notes "Even if " { $snippet "obj" } " is a word, it will be pushed as a literal."
$nl
"This operation is efficient and does not copy the quotation." }
"In most cases, loops should be written using high-level combinators (such as " { $link "sequences-combinators" } ") or tail recursion. However, sometimes, the best way to express intent is with a loop."
"This word is intended as a modifier. The normal " { $link while } " loop never executes the body if the predicate returns false on the first iteration. To ensure the body executes at least once, use " { $link do } ":"
"These shuffle words tend to make code difficult to read and to reason about. Code that uses them should almost always be rewritten using " { $link "locals" } " or " { $link "dataflow-combinators" } "."
"Shuffle words rearrange items at the top of the data stack as indicated by their stack effects. They provide simple data flow control between words. More complex data flow control is available with the " { $link "dataflow-combinators" } " and with " { $link "locals" } "."
"You can test if two references point to the same object (" { $emphasis "identity comparison" } "). This is rarely used; it is mostly useful with large, mutable objects where the object identity matters but the value is transient:"
"You can test if two objects are equal in a domain-specific sense, usually by being instances of the same class, and having equal slot values (" { $emphasis "value comparison" } "):"
