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Section 8.11.2.1
BOOL

immutable class BOOL < $IS_EQ, $IMMUTABLE, $INSTR, $ANCHORED_FMT

Inheritance map $IS_EQ $IMMUTABLE $INSTR $STR $BINARY $FMT $ANCHORED_FMT

Formal Types

types

SAME = bool ;
BOOL = bool ;

This class provides the functionality of the basic Boolean logic domain. BOOL objects represent boolean values and either have the value `true' or the value `false'. The pervasive class BOOL bool defines only the three fundamental operations and, or and not. This library class defines several additional operators and conversion routines.


create

This feature provides a mechanism for creating a truth value from an octet. An implementation is free to use any bit-pattern to represent the truth value, provided that it is the identical bit-pattern to that produced when the binstr feature is applied (producing a single element binary string).

create (
val : OCTET
) : SAME
Formal Signature
create1(val : OCTET) res : SAME
Pre-condition

Note that the selector applied to the binstr operation result is accessing the first (and only) component.

pre val = binstr(res)(1)
Post-condition
post card(res) = OCTET.card(val)

This routine returns the truth value corresponding to the bit-pattern in the argument val.


create

This feature creates a truth value from the given binary string (which must have a length of one.

create (
str : BINSTR
) : SAME
Formal Signature
create2(str : BINSTR) res : SAME
Pre-condition

The string argument must have a length of exactly 1, otherwise there is some unwanted binary data after the required octet.

pre BINSTR.size(str) = 1
Post-condition
post res = create1(str(1))

This routine returns the truth value corresponding to the single octet binary string.


create

This final variant of the create operation creates a truth value from the encoding of a string representation in the executing environment repertoire and encoding. The 'word' to be converted is expected to be in the language of the local culture.

create (
str : STR
) : SAME
Formal Signature
create3(bool_str : STR) res : SAME
Pre-condition
pre is_bool(str)
Post-condition

The string method is_prefix is defined in the class STR.

post STR.is_prefix(str(res),bool_str)

This routine returns the truth value corresponding to the text string argument. The actual characters required (and their encoding) are determined by the current cultural environment.

NOTE The internationally defined default characters for 'true' and 'false' are the digits '1' and '0' respectively in the local encoding. Most cultures will define pairs of values such as 'True/False' in English speaking cultures, 'Wahr/Falsch' in German speaking cultures, etc.

build

This feature, given a binary string cursor object as argument, will, depending on the value of the first/next octet, produce a truth value and move past that octet or, in the case that the octet bit-pattern is neither a representation for true nor for false will return false and the cursor will not be moved.

build (
cursor : BIN_CURSOR
) : SAME
Formal Signature
build1(cursor : BIN_CURSOR) res : SAME
Pre-condition
pre BIN_CURSOR.remaining(cursor) > 0
Post-condition
post res=create(BIN_CURSOR.item(cursor˜))
and BIN_CURSOR.remaining(cursor) + 1=BIN_CURSOR.remaining(cursor~)
or (BIN_CURSOR.remaining(cursor)=BIN_CURSOR.remaining(cursor~))

This routine builds a Boolean value from the first octet remaining in the cursor string. After the execution of this routine there is one octet less in the remainder of the cursor string.


build

This variant of build takes a text string cursor rather than a binary one, expecting to find the text string encoding form of a truth value at the first/next position in the text string associated with the cursor.

build (
cursor : STR_CURSOR
) : SAME
Formal Signature
build2(cursor : TEXT_CURSOR) res : SAME
Pre-condition
pre TEXT_CURSOR.remaining(cursor) > 0
Post-condition
post res=create(TEXT_CURSOR.item(cursor˜))
and TEXT_CURSOR.remaining(cursor) + 1=TEXT_CURSOR.remaining(cursor~)
or (TEXT_CURSOR.remaining(cursor)=TEXT_CURSOR.remaining(cursor~))

This routine builds a Boolean value from the text starting at the current cursor position in the cursor string. After the execution of this routine the cursor position will have moved one or more positions forward if the string represented a truth value. The cursor will not have moved if the string was not a truth value.


read

This feature provides a conditional conversion of the next octets in the binary string associated with the cursor. There are four possible outcomes -

NOTE The complexity of this operation arises since the result can only be true or false - ie there are only two values possible. The number of characters moved over in the binary string is therefore used to disambiguate the result returned.
read (
cursor : BIN_CURSOR
) : SAME
Formal Signature

read(cursor : BIN_CURSOR) res : SAME
Pre-condition
pre BIN_CURSOR.remaining(cursor) > 0
Post-condition

Note that the post-condition, while being true in the absence of implementation error, does not reflect the four possible outcomes.

post let truth : bool=BIN_CURSOR.item(cursor) in
((BIN_CURSOR.remaining(cursor)=BIN_CURSOR.remaining(cursor~))
and not res)
or ((BIN_CURSOR.remaining(cursor) + 1=BIN_CURSOR.remaining(cursor~))

This routine takes the next octet in the binary string as representing a Boolean value. If it does not then the cursor is not moved and false is returned. If this value is true then the next following octet is converted to a Boolean value which is returned, otherwise false is returned and only one octet has been taken from the remainder of the cursor string.


not

This feature provides the standard Boolean inversion operation.

not : SAME
Formal Signature

The name of the formal operation corresponding to 'not' has been modified since the word 'not' is a keyword in vdm-sl.

not_v(self : SAME) res : SAME
Post-condition
post res = not self

This feature returns the logical complement of self.


and

This feature provides the Boolean conjunction operation.

and (
other : SAME
) : SAME
Formal Signature

The name of the formal operation corresponding to 'and' has been modified since the word 'and' is a keyword in vdm-sl.

and_v(self : SAME, other : SAME) res : SAME
Post-condition
res = (self
and other)

This routine returns true if and only if self and other are both true, otherwise false.


or (
other : SAME
) : SAME

Formal Signature

or(self : SAME, other : SAME) res : SAME

Post-condition

res = (self

or other)

This routine returns true if and only if either self or other or both are true, otherwise false.


is_eq

This feature provides the logical equality operation for Boolean values. It may be used in infix logical expressions.

is_eq (
other : SAME
) : SAME
Formal Signature
is_eq(self : SAME, other : SAME) res : SAME
Post-condition
post res = (self
= other)

This routine returns true if and only if both self and other have the same value, otherwise false.


is_eq

This feature provides the logical equality operation for a logical value which may be 'hidden' in an abstract type and self. It may be used in infix logical expressions. Note, however, that object equality will be used if the argument is not of this type.

is_eq (
other : $OB
) : SAME
Formal Signature

The formal argument type is 'any object type', but an actual argument must, of course, be an instantiated object.

is_eq2(self : SAME, other : $OB) res : SAME
Post-condition
post res = (self = other)

This routine returns true if and only if both self and other have the same value, otherwise false. This version is provided for use where some abstract type object happens to derive from $IS_EQ. True can only be returned if the actual object is of this type.


is_bool

This feature returns a validity indicator if the string contained in the argument is a valid representation of either the value true or the value false. If empty then the corresponding indication is given, otherwise an out of range indication. The string does not have to be a complete 'word', rather it must be at least as long as needed to differentiate the two values - thus, in English where "True" and "False" are the two values, then the first character alone is all that is needed. If the rest of the word is there and does not correspond to 'rue' or 'alse' then, of course, out of range is returned.

is_bool (
str : STR
) : CONVERSION_RESULTS
Formal Signature
is_bool(str : STR) res : CONVERSION_RESULTS
Post-condition
post (res = All_Right
and (STR.is_prefix(str(true))
or STR.is_prefix(str(false))))
or (res = Empty
and STR.asize(str) = 0)
or (res = Out_of_Range)

This routine returns All_Right if str is a valid text representation of a truth value, Empty if the string was empty and Out_of_Range for any other string content.


xor

This is the first of those routines provided to complete the possible binary operations in the logical domain. They all have their usual mathematical meaning.

xor (
other : SAME
) : SAME
Formal Signature
xor(self : SAME, other : SAME) res : SAME
Post-condition
post res = ((self
and not other)
or (other
and not self))

This routine returns true if and only if only one of self and other is true, otherwise false. It is identical to a not equal predicate.


xnor

xnor (
other : SAME
) : SAME
Formal Signature
xnor(self : SAME, other : SAME) res : SAME
Post-condition
post res = ((self
and other)
or (not other
and not self))

This routine returns true if and only if self and other have the same logical value. It is identical to the is_eq predicate.


nand

nand (
other : SAME
) : SAME
Formal Signature
nand(self : SAME, other : SAME) res : SAME
Post-condition
post res = not (self
and other)

This routine returns the logical complement of the result of anding self and other.


nor

nor (
other : SAME
) : SAME
Formal Signature
nor(self : SAME, other : SAME) res : SAME
Post-condition
post res = not (self
or other)

This routine returns the logical complement of the result of oring self and other.



implies

implies (
other : SAME
) : SAME
Formal Signature
implies(self : SAME, other : SAME) res : SAME
Post-condition
post res = (not self
or other)

This routine returns if and only if self implies other. It is the same operation as nand_not.


and_rout

This routine is identical to the and operation built in to the language. It is provided for possible use as a bound routine.

and_rout (
other : SAME
) : SAME
Formal Signature
and_rout(self : SAME, other : SAME) res : SAME
Post-condition
post res = (self
and other)

This routine is the same as the and operation useful when making bound routines.


or_rout

This routine also corresponds to a built-in operator - or. It is provided for possible use as a bound routine.

or_rout (
other : SAME
) : SAME
Formal Signature
or_rout(self : SAME, other : SAME) res : SAME
Post-condition
post res = (self
or other)

This routine is the same as the or operation - provided for use when making bound routines.


and_not

and_not (
other : SAME
) : SAME
Formal Signature
and_not(self : SAME, other : SAME) res : SAME
Post-condition
post res = (self
and not other)

This routine returns the result of self and the complement of other.


or_not

or_not (
other : SAME
) : SAME
Formal Signature
or_not(self : SAME, other : SAME) res : SAME
Post-condition
post res = (self or not other)

This routine returns the result of self or the complement of other.


nand_not

nand_not (
other : SAME
) : SAME
Formal Signature
nand_not(self : SAME, other : SAME) res : SAME
Post-condition
post res = not (self and not other)

This routine returns the result of self nanded with the complement of other. It is the same as the complement of self or other.


nor_not

nor_not (
other : SAME
) : SAME
Formal Signature
nor_not(self : SAME, other : SAME) res : SAME
Post-condition
post res = not (self and other)

This routine returns the result of self nored with the complement of other. It is the same as the complement of self and other.


card

This operation is provided solely for backward compatibility with earlier versions of the library. It returns the value 1 when self is true and the value zero otherwise.

card : CARD
Formal Signature
card(self : SAME) res : CARD
Post-condition
post (self and (res = 1))
or (not self and (res = 0))

This routine returns the value 1 if self is true, otherwise the value zero.


binstr

This routine converts the logical value into a single octet binary string. The bit-pattern used shall be such that creating a new value from the result shall have the same values as self.

binstr : BINSTR
Formal Signature
binstr(self : SAME) res : BINSTR
Post-condition

Note that this post-condition cannot be converted into executable Sather post-condition as it is mutually recursive with the 'inverse' creation operation.

post create(res(1)) = self
and (BINSTR.size(res) = 1)

This routine returns a single element binary string which contains a bit pattern such that creation from an octet would produce the same value as self.


write

This routine appends the value of self as a single octet to the external binary file indicated by the argument.

write (
fyle : BIN_FILE
)
Formal Signature
write(self : SAME, fyle : BIN_FILE)
Pre-condition
pre BIN_FILE.writable(fyle)
Post-condition
post fyle = BIN_FILE.plus(fyle,binstr(self))

This routine appends a binary representation of self to the given binary file.


str

This is the first of two text string representation creation routines. It returns a text string encoding in the given language and encoding. Note that this may not necessarily be representable on a local rendering engine.

str (
lib : LIBCHARS
) : STR
Formal Signature
str1(self : SAME, lib : LIBCHARS) res : STR
Post-condition

Although the post-condition below will be true if the local and given culture are the same, this may well not be the case when they are different!

post create(res) = self

This routine provides a string representation of self in the given repertoire and encoding. The rules for forming the actual representation are defined by the Sather system resources and library cultural definitions.


str

This version of the str operation produces a text string from the value of self in the execution environment culture and encoding. This should normally be representable by a local rendering engine.

str : STR
Formal Signature
str2(self : SAME) res : STR
Post-condition
post create(res) = self

This routine provides a string representation of self in the default repertoire and encoding. The rules for forming the actual representation are defined by the Sather system resources and library cultural definitions.


fmt

This routine is provided for use by the formatting facilities of the Representation section of this library. It is included here since this class provides the string conversion facility. Note that this version of fmt makes use of a given culture in addition to the format descriptor. The format descriptor may be used directly, however, since it is produced as part of the formatting operation, this is not expected to be common usage.

fmt (
fmt : ANCHORED_DESCR ;
lib : LIBCHARS
) : STR
Formal Signature
fmt1(self : SAME, format : ANCHORED_DESCR, lib : LIBCHARS) res : STR
Post-condition

The very nature of this operation, being dynamically determinable during executioin only provides for no realisable formal specification post-condition, rather the informal statement that a formatted representation of self shall be returned.

This routine returns the formatted string representation of self in accordance with the string format in the given repertoire and encoding. This provides special case treatment where the leading component is exactly one - it reduces the value string to the single leading character - which is therefore expected to differ for the two values!


fmt

This version of fmt creates the result in the culture and coding of the current execution environment.

fmt (
fmt : ANCHORED_DESCR ;
) : STR
Formal Signature
fmt2(self : SAME, format : ANCHORED_DESCR) res : STR
Post-condition

The very nature of this operation, being dynamically determinable during executioin only provides for no realisable formal specification post-condition, rather the informal statement that a formatted representation of self shall be returned.

This routine returns the formatted string representation of self in accordance with the string format in the default repertoire and encoding. This provides special case treatment where the leading component is exactly one - it reduces the value string to the single leading character - which is therefore expected to differ for the two values!


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