org.extex.unit.etex.conditional
Class Unless

java.lang.Object
  org.extex.interpreter.type.AbstractCode
      org.extex.unit.etex.conditional.Unless

All Implemented Interfaces:

java.io.Serializable, Code, ExpandableCode, PrefixCode

public class Unless
extends AbstractCode
implements ExpandableCode, PrefixCode

This class provides an implementation for the primitive \if.

The Primitive \unless

Copied of the eTeX reference.

TeX has, by design, a rather sparse set of conditional primitives: \ifeof, \ifodd, \ifvoid, etc., have no complementary counterparts. Whilst this normally poses no problems since each accepts both a \then (implicit) and an \else (explicit) part, they fall down when used as the final \if... of a \loop ... \if ... \repeat construct, since no \else is allowed after the final \if.... \unless allows the sense of all Boolean conditionals to be inverted, and thus (for example) \unless \ifeof yields true iff end-of-file has not yet been reached.

The formal description of this primitive is the following:

TODO missing documentation

Examples:

    \unless\if\x\y not ok \fi  

Version:

$Revision: 4770 $

Author:

Gerd Neugebauer, Sebastian Waschik

See Also:

Serialized Form

Field Summary

protected static long

serialVersionUID The field serialVersionUID contains the version number for the serialization.

Constructor Summary

Unless(CodeToken token)
Creates a new object.

Method Summary

void	execute(Flags prefix, Context context, TokenSource source, Typesetter typesetter) This method takes the first token and executes it.
void	expand(Flags prefix, Context context, TokenSource source, Typesetter typesetter) This method takes the first token and expands it.

Methods inherited from class org.extex.interpreter.type.AbstractCode

getLocalizer, getName, getToken, isIf, isOuter, readResolve, toString, toText, toText

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

serialVersionUID

protected static final long serialVersionUID

The field serialVersionUID contains the version number for the serialization.

See Also:

Constant Field Values

Constructor Detail

Unless

public Unless(CodeToken token)

Creates a new object.

Parameters:

token - the initial token for the primitive

Method Detail

execute

public void execute(Flags prefix,
                    Context context,
                    TokenSource source,
                    Typesetter typesetter)
             throws HelpingException,
                    TypesetterException

This method takes the first token and executes it. The result is placed on the stack. This operation might have side effects. To execute a token it might be necessary to consume further tokens.

Specified by:

execute in interface Code

Overrides:

execute in class AbstractCode

Parameters:

prefix - the prefix controlling the execution

context - the interpreter context

source - the token source

typesetter - the typesetter

Throws:

HelpingException - in case of an error

TypesetterException - in case of an error in the typesetter

See Also:

AbstractCode.execute( org.extex.interpreter.Flags, org.extex.interpreter.context.Context, org.extex.interpreter.TokenSource, org.extex.typesetter.Typesetter)

expand

public void expand(Flags prefix,
                   Context context,
                   TokenSource source,
                   Typesetter typesetter)
            throws HelpingException,
                   TypesetterException

This method takes the first token and expands it. The result is placed on the stack. This means that expandable code does one step of expansion and puts the result on the stack. To expand a token it might be necessary to consume further tokens.

Specified by:

expand in interface ExpandableCode

Parameters:

prefix - the prefix flags controlling the expansion

context - the interpreter context

source - the token source

typesetter - the typesetter

Throws:

HelpingException - in case of an error

TypesetterException - in case of an error in the typesetter

See Also:

ExpandableCode.expand( org.extex.interpreter.Flags, org.extex.interpreter.context.Context, org.extex.interpreter.TokenSource, org.extex.typesetter.Typesetter)