[pspp-builds.git] / doc / language.texi

@node Language, Expressions, Invocation, Top
@chapter The PSPP language
@cindex language, PSPP
@cindex PSPP, language

@quotation
@strong{Please note:} PSPP is not even close to completion.
Only a few actual statistical procedures are implemented.  PSPP
is a work in progress.
@end quotation

This chapter discusses elements common to many PSPP commands.
Later chapters will describe individual commands in detail.

@menu
* Tokens::                      Characters combine to form tokens.
* Commands::                    Tokens combine to form commands.
* Types of Commands::           Commands come in several flavors.
* Order of Commands::           Commands combine to form syntax files.
* Missing Observations::        Handling missing observations.
* Variables::                   The unit of data storage.
* Files::                       Files used by PSPP.
* BNF::                         How command syntax is described.
@end menu

@node Tokens, Commands, Language, Language
@section Tokens
@cindex language, lexical analysis
@cindex language, tokens
@cindex tokens
@cindex lexical analysis
@cindex lexemes

PSPP divides most syntax file lines into series of short chunks
called @dfn{tokens}, @dfn{lexical elements}, or @dfn{lexemes}.  These
tokens are then grouped to form commands, each of which tells
PSPP to take some action---read in data, write out data, perform
a statistical procedure, etc.  The process of dividing input into tokens
is @dfn{tokenization}, or @dfn{lexical analysis}.  Each type of token is
described below.

@cindex delimiters
@cindex whitespace
Tokens must be separated from each other by @dfn{delimiters}.
Delimiters include whitespace (spaces, tabs, carriage returns, line
feeds, vertical tabs), punctuation (commas, forward slashes, etc.), and
operators (plus, minus, times, divide, etc.)  Note that while whitespace
only separates tokens, other delimiters are tokens in themselves.

@table @strong
@cindex identifiers
@item Identifiers
Identifiers are names that specify variable names, commands, or command
details.

@itemize @bullet
@item
The first character in an identifier must be a letter, @samp{#}, or
@samp{@@}.  Some system identifiers begin with @samp{$}, but
user-defined variables' names may not begin with @samp{$}.

@item
The remaining characters in the identifier must be letters, digits, or
one of the following special characters: 

@example
.  _  $  #  @@
@end example

@item
@cindex variable names
@cindex names, variable
Variable names may be any length, but only the first 8 characters are
significant.

@item
@cindex case-sensitivity
Identifiers are not case-sensitive: @code{foobar}, @code{Foobar},
@code{FooBar}, @code{FOOBAR}, and @code{FoObaR} are different
representations of the same identifier.

@item
@cindex keywords
Identifiers other than variable names may be abbreviated to their first
3 characters if this abbreviation is unambiguous.  These identifiers are
often called @dfn{keywords}.  (Unique abbreviations of 3 or more
characters are also accepted: @samp{FRE}, @samp{FREQ}, and
@samp{FREQUENCIES} are equivalent when the last is a keyword.)

@item
Whether an identifier is a keyword depends on the context.

@item
@cindex keywords, reserved
@cindex reserved keywords
Some keywords are reserved.  These keywords may not be used in any
context besides those explicitly described in this manual.  The reserved
keywords are:

@example
ALL  AND  BY  EQ  GE  GT  LE  LT  NE  NOT  OR  TO  WITH
@end example

@item 
Since keywords are identifiers, all the rules for identifiers apply.
Specifically, they must be delimited as are other identifiers:
@code{WITH} is a reserved keyword, but @code{WITHOUT} is a valid
variable name.
@end itemize

@cindex @samp{.}
@cindex period
@cindex variable names, ending with period
@strong{Caution:} It is legal to end a variable name with a period, but
@emph{don't do it!}  The variable name will be misinterpreted when it is
the final token on a line: @code{FOO.} will be divided into two separate
tokens, @samp{FOO} and @samp{.}, the @dfn{terminal dot}.
@xref{Commands, , Forming commands of tokens}.

@item Numbers
@cindex numbers
@cindex integers
@cindex reals
Numbers may be specified as integers or reals.  Integers are internally
converted into reals.  Scientific notation is not supported.  Here are
some examples of valid numbers:

@example
1234  3.14159265359  .707106781185  8945.
@end example

@strong{Caution:} The last example will be interpreted as two tokens,
@samp{8945} and @samp{.}, if it is the last token on a line.

@item Strings
@cindex strings
@cindex @samp{'}
@cindex @samp{"}
@cindex case-sensitivity
Strings are literal sequences of characters enclosed in pairs of single
quotes (@samp{'}) or double quotes (@samp{"}).

@itemize @bullet
@item
Whitespace and case of letters @emph{are} significant inside strings.
@item
Whitespace characters inside a string are not delimiters.
@item
To include single-quote characters in a string, enclose the string in
double quotes.
@item
To include double-quote characters in a string, enclose the string in
single quotes.
@item
It is not possible to put both single- and double-quote characters
inside one string.
@end itemize

@item Hexstrings
@cindex hexstrings
Hexstrings are string variants that use hex digits to specify
characters.

@itemize @bullet
@item
A hexstring may be used anywhere that an ordinary string is allowed.

@item
@cindex @samp{X'}
@cindex @samp{'}
A hexstring begins with @samp{X'} or @samp{x'}, and ends with @samp{'}.

@cindex whitespace
@item
No whitespace is allowed between the initial @samp{X} and @samp{'}.

@item
Double quotes @samp{"} may be used in place of single quotes @samp{'} if
done in both places.

@item
Each pair of hex digits is internally changed into a single character
with the given value.

@item
If there is an odd number of hex digits, the missing last digit is
assumed to be @samp{0}.

@item
@cindex portability
@strong{Please note:} Use of hexstrings is nonportable because the same
numeric values are associated with different glyphs by different
operating systems.  Therefore, their use should be confined to syntax
files that will not be widely distributed.

@item
@cindex characters, reserved
@cindex 0
@cindex whitespace
@strong{Please note also:} The character with value 00 is reserved for
internal use by PSPP.  Its use in strings causes an error and
replacement with a blank space (in ASCII, hex 20, decimal 32).
@end itemize

@item Punctuation
@cindex punctuation
Punctuation separates tokens; punctuators are delimiters.  These are the
punctuation characters:

@example
,  /  =  (  )
@end example

@item Operators
@cindex operators
Operators describe mathematical operations.  Some operators are delimiters:

@example
(  )  +  -  *  /  **
@end example

Many of the above operators are also punctuators.  Punctuators are
distinguished from operators by context. 

The other operators are all reserved keywords.  None of these are
delimiters:

@example
AND  EQ  GE  GT  LE  LT  NE  OR
@end example

@item Terminal Dot
@cindex terminal dot
@cindex dot, terminal
@cindex period
@cindex @samp{.}
A period (@samp{.}) at the end of a line (except for whitespace) is one
type of a @dfn{terminal dot}, although not every terminal dot is a
period at the end of a line.  @xref{Commands, , Forming commands of
tokens}.  A period is a terminal dot @emph{only}
when it is at the end of a line; otherwise it is part of a
floating-point number.  (A period outside a number in the middle of a
line is an error.)

@quotation
@cindex terminal dot, changing
@cindex dot, terminal, changing
@strong{Please note:} The character used for the @dfn{terminal dot}
can be changed with @cmd{SET}'s ENDCMD subcommand (@pxref{SET}).  This
is strongly discouraged, and throughout all the remainder of this
manual it will be assumed that the default setting is in effect.
@end quotation

@end table

@node Commands, Types of Commands, Tokens, Language
@section Forming commands of tokens

@cindex PSPP, command structure
@cindex language, command structure
@cindex commands, structure

Most PSPP commands share a common structure, diagrammed below:

@example
@var{cmd}@dots{} [@var{sbc}[=][@var{spec} [[,]@var{spec}]@dots{}]] [[/[=][@var{spec} [[,]@var{spec}]@dots{}]]@dots{}].
@end example

@cindex @samp{[  ]}
In the above, rather daunting, expression, pairs of square brackets
(@samp{[ ]}) indicate optional elements, and names such as @var{cmd}
indicate parts of the syntax that vary from command to command.
Ellipses (@samp{...}) indicate that the preceding part may be repeated
an arbitrary number of times.  Let's pick apart what it says above:

@itemize @bullet
@cindex commands, names
@item
A command begins with a command name of one or more keywords, such as
@cmd{FREQUENCIES}, @cmd{DATA LIST}, or @cmd{N OF CASES}.  @var{cmd}
may be abbreviated to its first word if that is unambiguous; each word
in @var{cmd} may be abbreviated to a unique prefix of three or more
characters as described above.

@cindex subcommands
@item
The command name may be followed by one or more @dfn{subcommands}:

@itemize @minus
@item
Each subcommand begins with a unique keyword, indicated by @var{sbc}
above.  This is analogous to the command name.

@item
The subcommand name is optionally followed by an equals sign (@samp{=}).

@item
Some subcommands accept a series of one or more specifications
(@var{spec}), optionally separated by commas.

@item
Each subcommand must be separated from the next (if any) by a forward
slash (@samp{/}).
@end itemize

@cindex dot, terminal
@cindex terminal dot
@item
Each command must be terminated with a @dfn{terminal dot}.  
The terminal dot may be given one of three ways:

@itemize @minus
@item
(most commonly) A period character at the very end of a line, as
described above.

@item
(only if NULLINE is on: @xref{SET, , Setting user preferences}, for more
details.)  A completely blank line.

@item
(in batch mode only) Any line that is not indented from the left side of
the page causes a terminal dot to be inserted before that line.
Therefore, each command begins with a line that is flush left, followed
by zero or more lines that are indented one or more characters from the
left margin.

In batch mode, PSPP will ignore a plus sign, minus sign, or period
(@samp{+}, @samp{@minus{}}, or @samp{.}) as the first character in a
line.  Any of these characters as the first character on a line will
begin a new command.  This allows for visual indentation of a command
without that command being considered part of the previous command.

PSPP is in batch mode when it is reading input from a file, rather
than from an interactive user.  Note that the other forms of the
terminal dot may also be used in batch mode.

Sometimes, one encounters syntax files that are intended to be
interpreted in interactive mode rather than batch mode (for instance,
this can happen if a session log file is used directly as a syntax
file).  When this occurs, use the @samp{-i} command line option to force
interpretation in interactive mode (@pxref{Language control options}).
@end itemize
@end itemize

PSPP ignores empty commands when they are generated by the above
rules.  Note that, as a consequence of these rules, each command must
begin on a new line.

@node Types of Commands, Order of Commands, Commands, Language
@section Types of Commands

Commands in PSPP are divided roughly into six categories:

@table @strong
@item Utility commands
@cindex utility commands
Set or display various global options that affect PSPP operations.
May appear anywhere in a syntax file.  @xref{Utilities, , Utility
commands}.

@item File definition commands
@cindex file definition commands
Give instructions for reading data from text files or from special
binary ``system files''.  Most of these commands discard any previous
data or variables to replace it with the new data and
variables.  At least one must appear before the first command in any of
the categories below.  @xref{Data Input and Output}.

@item Input program commands
@cindex input program commands
Though rarely used, these provide powerful tools for reading data files
in arbitrary textual or binary formats.  @xref{INPUT PROGRAM}.

@item Transformations
@cindex transformations
Perform operations on data and write data to output files.  Transformations
are not carried out until a procedure is executed.  

@item Restricted transformations
@cindex restricted transformations
Same as transformations for most purposes.  @xref{Order of Commands}, for a
detailed description of the differences.

@item Procedures
@cindex procedures
Analyze data, writing results of analyses to the listing file.  Cause
transformations specified earlier in the file to be performed.  In a
more general sense, a @dfn{procedure} is any command that causes the
active file (the data) to be read.
@end table

@node Order of Commands, Missing Observations, Types of Commands, Language
@section Order of Commands
@cindex commands, ordering
@cindex order of commands

PSPP does not place many restrictions on ordering of commands.
The main restriction is that variables must be defined with one of the
file-definition commands before they are otherwise referred to.

Of course, there are specific rules, for those who are interested.
PSPP possesses five internal states, called initial, INPUT PROGRAM,
FILE TYPE, transformation, and procedure states.  (Please note the
distinction between the @cmd{INPUT PROGRAM} and @cmd{FILE TYPE}
@emph{commands} and the INPUT PROGRAM and FILE TYPE @emph{states}.)

PSPP starts up in the initial state.  Each successful completion
of a command may cause a state transition.  Each type of command has its
own rules for state transitions:

@table @strong
@item Utility commands
@itemize @bullet
@item
Legal in all states.
@item
Do not cause state transitions.  Exception: when @cmd{N OF CASES}
is executed in the procedure state, it causes a transition to the
transformation state.
@end itemize

@item @cmd{DATA LIST}
@itemize @bullet
@item
Legal in all states.
@item
When executed in the initial or procedure state, causes a transition to
the transformation state.  
@item
Clears the active file if executed in the procedure or transformation
state.
@end itemize

@item @cmd{INPUT PROGRAM}
@itemize @bullet
@item
Invalid in INPUT PROGRAM and FILE TYPE states.
@item
Causes a transition to the INPUT PROGRAM state.  
@item
Clears the active file.
@end itemize

@item @cmd{FILE TYPE}
@itemize @bullet
@item
Invalid in INPUT PROGRAM and FILE TYPE states.
@item
Causes a transition to the FILE TYPE state.
@item
Clears the active file.
@end itemize

@item Other file definition commands
@itemize @bullet
@item
Invalid in INPUT PROGRAM and FILE TYPE states.
@item
Cause a transition to the transformation state.
@item
Clear the active file, except for @cmd{ADD FILES}, @cmd{MATCH FILES},
and @cmd{UPDATE}.
@end itemize

@item Transformations
@itemize @bullet
@item
Invalid in initial and FILE TYPE states.
@item
Cause a transition to the transformation state.
@end itemize

@item Restricted transformations
@itemize @bullet
@item
Invalid in initial, INPUT PROGRAM, and FILE TYPE states.
@item
Cause a transition to the transformation state.
@end itemize

@item Procedures
@itemize @bullet
@item
Invalid in initial, INPUT PROGRAM, and FILE TYPE states.
@item
Cause a transition to the procedure state.
@end itemize
@end table

@node Missing Observations, Variables, Order of Commands, Language
@section Handling missing observations
@cindex missing values
@cindex values, missing

PSPP includes special support for unknown numeric data values.
Missing observations are assigned a special value, called the
@dfn{system-missing value}.  This ``value'' actually indicates the
absence of value; it means that the actual value is unknown.  Procedures
automatically exclude from analyses those observations or cases that
have missing values.  Whether single observations or entire cases are
excluded depends on the procedure.

The system-missing value exists only for numeric variables.  String
variables always have a defined value, even if it is only a string of
spaces.

Variables, whether numeric or string, can have designated
@dfn{user-missing values}.  Every user-missing value is an actual value
for that variable.  However, most of the time user-missing values are
treated in the same way as the system-missing value.  String variables
that are wider than a certain width, usually 8 characters (depending on
computer architecture), cannot have user-missing values.

For more information on missing values, see the following sections:
@ref{Variables}, @ref{MISSING VALUES}, @ref{Expressions}.  See also the
documentation on individual procedures for information on how they
handle missing values.

@node Variables, Files, Missing Observations, Language
@section Variables
@cindex variables
@cindex dictionary

Variables are the basic unit of data storage in PSPP.  All the
variables in a file taken together, apart from any associated data, are
said to form a @dfn{dictionary}.  
Some details of variables are described in the sections below.

@menu
* Attributes::                  Attributes of variables.
* System Variables::            Variables automatically defined by PSPP.
* Sets of Variables::           Lists of variable names.
* Input/Output Formats::        Input and output formats.
* Scratch Variables::           Variables deleted by procedures.
@end menu

@node Attributes, System Variables, Variables, Variables
@subsection Attributes of Variables
@cindex variables, attributes of
@cindex attributes of variables
Each variable has a number of attributes, including:

@table @strong
@item Name
This is an identifier.  Each variable must have a different name.
@xref{Tokens}.

@cindex variables, type
@cindex type of variables
@item Type
Numeric or string.

@cindex variables, width
@cindex width of variables
@item Width
(string variables only) String variables with a width of 8 characters or
fewer are called @dfn{short string variables}.  Short string variables
can be used in many procedures where @dfn{long string variables} (those
with widths greater than 8) are not allowed.

@quotation
@strong{Please note:} Certain systems may consider strings longer than 8
characters to be short strings.  Eight characters represents a minimum
figure for the maximum length of a short string.
@end quotation

@item Position
Variables in the dictionary are arranged in a specific order.
@cmd{DISPLAY} can be used to show this order: see @ref{DISPLAY}.

@item Initialization
Either reinitialized to 0 or spaces for each case, or left at its
existing value.  @xref{LEAVE}.

@cindex missing values
@cindex values, missing
@item Missing values
Optionally, up to three values, or a range of values, or a specific
value plus a range, can be specified as @dfn{user-missing values}.
There is also a @dfn{system-missing value} that is assigned to an
observation when there is no other obvious value for that observation.
Observations with missing values are automatically excluded from
analyses.  User-missing values are actual data values, while the
system-missing value is not a value at all.  @xref{Missing Observations}.

@cindex variable labels
@cindex labels, variable
@item Variable label
A string that describes the variable.  @xref{VARIABLE LABELS}.

@cindex value labels
@cindex labels, value
@item Value label
Optionally, these associate each possible value of the variable with a
string.  @xref{VALUE LABELS}.

@cindex print format
@item Print format
Display width, format, and (for numeric variables) number of decimal
places.  This attribute does not affect how data are stored, just how
they are displayed.  Example: a width of 8, with 2 decimal places.
@xref{PRINT FORMATS}.

@cindex write format
@item Write format
Similar to print format, but used by certain commands that are
designed to write to binary files.  @xref{WRITE FORMATS}.
@end table

@node System Variables, Sets of Variables, Attributes, Variables
@subsection Variables Automatically Defined by PSPP
@cindex system variables
@cindex variables, system

There are seven system variables.  These are not like ordinary
variables, as they are not stored in each case.  They can only be used
in expressions.  These system variables, whose values and output formats
cannot be modified, are described below.

@table @code
@cindex @code{$CASENUM}
@item $CASENUM
Case number of the case at the moment.  This changes as cases are
shuffled around.

@cindex @code{$DATE}
@item $DATE
Date the PSPP process was started, in format A9, following the
pattern @code{DD MMM YY}.

@cindex @code{$JDATE}
@item $JDATE
Number of days between 15 Oct 1582 and the time the PSPP process
was started.

@cindex @code{$LENGTH}
@item $LENGTH
Page length, in lines, in format F11.

@cindex @code{$SYSMIS}
@item $SYSMIS
System missing value, in format F1.

@cindex @code{$TIME}
@item $TIME
Number of seconds between midnight 14 Oct 1582 and the time the active file
was read, in format F20.

@cindex @code{$WIDTH}
@item $WIDTH
Page width, in characters, in format F3.
@end table

@node Sets of Variables, Input/Output Formats, System Variables, Variables
@subsection Lists of variable names
@cindex TO convention
@cindex convention, TO

There are several ways to specify a set of variables:

@enumerate
@item
(Most commonly.)  List the variable names one after another, optionally
separating them by commas.

@cindex @code{TO}
@item
(This method cannot be used on commands that define the dictionary, such
as @cmd{DATA LIST}.)  The syntax is the names of two existing variables,
separated by the reserved keyword @code{TO}.  The meaning is to include
every variable in the dictionary between and including the variables
specified.  For instance, if the dictionary contains six variables with
the names @code{ID}, @code{X1}, @code{X2}, @code{GOAL}, @code{MET}, and
@code{NEXTGOAL}, in that order, then @code{X2 TO MET} would include
variables @code{X2}, @code{GOAL}, and @code{MET}.

@item
(This method can be used only on commands that define the dictionary,
such as @cmd{DATA LIST}.)  It is used to define sequences of variables
that end in consecutive integers.  The syntax is two identifiers that
end in numbers.  This method is best illustrated with examples:

@itemize @bullet
@item
The syntax @code{X1 TO X5} defines 5 variables:

@itemize @minus
@item
X1
@item
X2
@item
X3
@item
X4
@item
X5
@end itemize

@item
The syntax @code{ITEM0008 TO ITEM0013} defines 6 variables:

@itemize @minus
@item
ITEM0008
@item
ITEM0009
@item
ITEM0010
@item
ITEM0011
@item
ITEM0012
@item
ITEM0013
@end itemize

@item
Each of the syntaxes @code{QUES001 TO QUES9} and @code{QUES6 TO QUES3}
are invalid, although for different reasons, which should be evident.
@end itemize

Note that after a set of variables has been defined with @cmd{DATA LIST}
or another command with this method, the same set can be referenced on
later commands using the same syntax.

@item
The above methods can be combined, either one after another or delimited
by commas.  For instance, the combined syntax @code{A Q5 TO Q8 X TO Z}
is legal as long as each part @code{A}, @code{Q5 TO Q8}, @code{X TO Z}
is individually legal.
@end enumerate

@node Input/Output Formats, Scratch Variables, Sets of Variables, Variables
@subsection Input and Output Formats

Data that PSPP inputs and outputs must have one of a number of formats.
These formats are described, in general, by a format specification of
the form @code{NAMEw.d}, where @var{name} is the
format name and @var{w} is a field width.  @var{d} is the optional
desired number of decimal places, if appropriate.  If @var{d} is not
included then it is assumed to be 0.  Some formats do not allow @var{d}
to be specified.

When an input format is specified on @cmd{DATA LIST} or another
command, then
it is converted to an output format for the purposes of @cmd{PRINT}
and other
data output commands.  For most purposes, input and output formats are
the same; the salient differences are described below.

Below are listed the input and output formats supported by PSPP.  If an
input format is mapped to a different output format by default, then
that mapping is indicated with @result{}.  Each format has the listed
bounds on input width (iw) and output width (ow).

The standard numeric input and output formats are given in the following
table:

@table @asis
@item Fw.d: 1 <= iw,ow <= 40
Standard decimal format with @var{d} decimal places.  If the number is
too large to fit within the field width, it is expressed in scientific
notation (@code{1.2+34}) if w >= 6, with always at least two digits in
the exponent.  When used as an input format, scientific notation is
allowed but an E or an F must be used to introduce the exponent.

The default output format is the same as the input format, except if
@var{d} > 1.  In that case the output @var{w} is always made to be at
least 2 + @var{d}.

@item Ew.d: 1 <= iw <= 40; 6 <= ow <= 40
For input this is equivalent to F format except that no E or F is
require to introduce the exponent.  For output, produces scientific
notation in the form @code{1.2+34}.  There are always at least two
digits given in the exponent.

The default output @var{w} is the largest of the input @var{w}, the
input @var{d} + 7, and 10.  The default output @var{d} is the input
@var{d}, but at least 3.

@item COMMAw.d: 1 <= iw,ow <= 40
Equivalent to F format, except that groups of three digits are
comma-separated on output.  If the number is too large to express in the
field width, then first commas are eliminated, then if there is still
not enough space the number is expressed in scientific notation given
that w >= 6.  Commas are allowed and ignored when this is used as an
input format.  

@item DOTw.d: 1 <= iw,ow <= 40
Equivalent to COMMA format except that the roles of comma and decimal
point are interchanged.  However: If SET /DECIMAL=DOT is in effect, then
COMMA uses @samp{,} for a decimal point and DOT uses @samp{.} for a
decimal point.

@item DOLLARw.d: 1 <= iw <= 40; 2 <= ow <= 40
Equivalent to COMMA format, except that the number is prefixed by a
dollar sign (@samp{$}) if there is room.  On input the value is allowed
to be prefixed by a dollar sign, which is ignored.

The default output @var{w} is the input @var{w}, but at least 2.

@item PCTw.d: 2 <= iw,ow <= 40
Equivalent to F format, except that the number is suffixed by a percent
sign (@samp{%}) if there is room.  On input the value is allowed to be
suffixed by a percent sign, which is ignored.

The default output @var{w} is the input @var{w}, but at least 2.

@item Nw.d: 1 <= iw,ow <= 40
Only digits are allowed within the field width.  The decimal point is
assumed to be @var{d} digits from the right margin.

The default output format is F with the same @var{w} and @var{d}, except
if @var{d} > 1.  In that case the output @var{w} is always made to be at
least 2 + @var{d}.

@item Zw.d @result{} F: 1 <= iw,ow <= 40
Zoned decimal input.  If you need to use this then you know how.

@item IBw.d @result{} F: 1 <= iw,ow <= 8
Integer binary format.  The field is interpreted as a fixed-point
positive or negative binary number in two's-complement notation.  The
location of the decimal point is implied.  Endianness is the same as the
host machine.

The default output format is F8.2 if @var{d} is 0.  Otherwise it is F,
with output @var{w} as 9 + input @var{d} and output @var{d} as input
@var{d}.

@item PIB @result{} F: 1 <= iw,ow <= 8
Positive integer binary format.  The field is interpreted as a
fixed-point positive binary number.  The location of the decimal point
is implied.  Endianness is teh same as the host machine.

The default output format follows the rules for IB format.

@item Pw.d @result{} F: 1 <= iw,ow <= 16
Binary coded decimal format.  Each byte from left to right, except the
rightmost, represents two digits.  The upper nibble of each byte is more
significant.  The upper nibble of the final byte is the least
significant digit.  The lower nibble of the final byte is the sign; a
value of D represents a negative sign and all other values are
considered positive.  The decimal point is implied.

The default output format follows the rules for IB format.

@item PKw.d @result{} F: 1 <= iw,ow <= 16
Positive binary code decimal format.  Same as P but the last byte is the
same as the others.

The default output format follows the rules for IB format.

@item RBw @result{} F: 2 <= iw,ow <= 8

Binary C architecture-dependent ``double'' format.  For a standard
IEEE754 implementation @var{w} should be 8.

The default output format follows the rules for IB format.

@item PIBHEXw.d @result{} F: 2 <= iw,ow <= 16
PIB format encoded as textual hex digit pairs.  @var{w} must be even.

The input width is mapped to a default output width as follows:
2@result{}4, 4@result{}6, 6@result{}9, 8@result{}11, 10@result{}14,
12@result{}16, 14@result{}18, 16@result{}21.  No allowances are made for
decimal places.

@item RBHEXw @result{} F: 4 <= iw,ow <= 16

RB format encoded as textual hex digits pairs.  @var{w} must be even.

The default output format is F8.2.

@item CCAw.d: 1 <= ow <= 40
@itemx CCBw.d: 1 <= ow <= 40
@itemx CCCw.d: 1 <= ow <= 40
@itemx CCDw.d: 1 <= ow <= 40
@itemx CCEw.d: 1 <= ow <= 40

User-defined custom currency formats.  May not be used as an input
format.  @xref{SET}, for more details.
@end table

The date and time numeric input and output formats accept a number of
possible formats.  Before describing the formats themselves, some
definitions of the elements that make up their formats will be helpful:

@table @dfn
@item leader
All formats accept an optional whitespace leader.

@item day
An integer between 1 and 31 representing the day of month.

@item day-count
An integer representing a number of days.

@item date-delimiter
One or more characters of whitespace or the following characters:
@code{- / . ,}

@item month
A month name in one of the following forms:
@itemize @bullet
@item
An integer between 1 and 12.
@item
Roman numerals representing an integer between 1 and 12.
@item
At least the first three characters of an English month name (January,
February, @dots{}).
@end itemize

@item year
An integer year number between 1582 and 19999, or between 1 and 199.
Years between 1 and 199 will have 1900 added.

@item julian
A single number with a year number in the first 2, 3, or 4 digits (as
above) and the day number within the year in the last 3 digits.

@item quarter
An integer between 1 and 4 representing a quarter.

@item q-delimiter
The letter @samp{Q} or @samp{q}.

@item week
An integer between 1 and 53 representing a week within a year.

@item wk-delimiter
The letters @samp{wk} in any case.

@item time-delimiter
At least one characters of whitespace or @samp{:} or @samp{.}.

@item hour
An integer greater than 0 representing an hour.

@item minute
An integer between 0 and 59 representing a minute within an hour.

@item opt-second
Optionally, a time-delimiter followed by a real number representing a
number of seconds.

@item hour24
An integer between 0 and 23 representing an hour within a day.

@item weekday
At least the first two characters of an English day word.

@item spaces
Any amount or no amount of whitespace.

@item sign
An optional positive or negative sign.

@item trailer
All formats accept an optional whitespace trailer.
@end table

The date input formats are strung together from the above pieces.  On
output, the date formats are always printed in a single canonical
manner, based on field width.  The date input and output formats are
described below:

@table @asis
@item DATEw: 9 <= iw,ow <= 40
Date format. Input format: leader + day + date-delimiter +
month + date-delimiter + year + trailer.  Output format: DD-MMM-YY for
@var{w} < 11, DD-MMM-YYYY otherwise.

@item EDATEw: 8 <= iw,ow <= 40
European date format.  Input format same as DATE.  Output format:
DD.MM.YY for @var{w} < 10, DD.MM.YYYY otherwise.

@item SDATEw: 8 <= iw,ow <= 40
Standard date format. Input format: leader + year + date-delimiter +
month + date-delimiter + day + trailer.  Output format: YY/MM/DD for
@var{w} < 10, YYYY/MM/DD otherwise.

@item ADATEw: 8 <= iw,ow <= 40
American date format.  Input format: leader + month + date-delimiter +
day + date-delimiter + year + trailer.  Output format: MM/DD/YY for
@var{w} < 10, MM/DD/YYYY otherwise.

@item JDATEw: 5 <= iw,ow <= 40
Julian date format.  Input format: leader + julian + trailer.  Output
format: YYDDD for @var{w} < 7, YYYYDDD otherwise.

@item QYRw: 4 <= iw <= 40, 6 <= ow <= 40
Quarter/year format.  Input format: leader + quarter + q-delimiter +
year + trailer.  Output format: @samp{Q Q YY}, where the first
@samp{Q} is one of the digits 1, 2, 3, 4, if @var{w} < 8, @code{Q Q
YYYY} otherwise.

@item MOYRw: 6 <= iw,ow <= 40
Month/year format.  Input format: leader + month + date-delimiter + year
+ trailer.  Output format: @samp{MMM YY} for @var{w} < 8, @samp{MMM
YYYY} otherwise.

@item WKYRw: 6 <= iw <= 40, 8 <= ow <= 40
Week/year format.  Input format: leader + week + wk-delimiter + year +
trailer.  Output format: @samp{WW WK YY} for @var{w} < 10, @samp{WW WK
YYYY} otherwise.

@item DATETIMEw.d: 17 <= iw,ow <= 40
Date and time format.  Input format: leader + day + date-delimiter +
month + date-delimiter + yaer + time-delimiter + hour24 + time-delimiter
+ minute + opt-second.  Output format: @samp{DD-MMM-YYYY HH:MM}.  If
@var{w} > 19 then seconds @samp{:SS} is added.  If @var{w} > 22 and
@var{d} > 0 then fractional seconds @samp{.SS} are added.

@item TIMEw.d: 5 <= iw,ow <= 40
Time format.  Input format: leader + sign + spaces + hour +
time-delimiter + minute + opt-second.  Output format: @samp{HH:MM}.
Seconds and fractional seconds are available with @var{w} of at least 8
and 10, respectively.

@item DTIMEw.d: 1 <= iw <= 40, 8 <= ow <= 40
Time format with day count.  Input format: leader + sign + spaces +
day-count + time-delimiter + hour + time-delimiter + minute +
opt-second.  Output format: @samp{DD HH:MM}.  Seconds and fractional
seconds are available with @var{w} of at least 8 and 10, respectively.

@item WKDAYw: 2 <= iw,ow <= 40
A weekday as a number between 1 and 7, where 1 is Sunday.  Input format:
leader + weekday + trailer.  Output format: as many characters, in all
capital letters, of the English name of the weekday as will fit in the
field width.

@item MONTHw: 3 <= iw,ow <= 40
A month as a number between 1 and 12, where 1 is January.  Input format:
leader + month + trailer.  Output format: as many character, in all
capital letters, of the English name of the month as will fit in the
field width.
@end table

There are only two formats that may be used with string variables:

@table @asis
@item Aw: 1 <= iw <= 255, 1 <= ow <= 254
The entire field is treated as a string value.

@item AHEXw @result{} A: 2 <= iw <= 254; 2 <= ow <= 510
The field is composed of characters in a string encoded as textual hex
digit pairs.

The default output @var{w} is half the input @var{w}.
@end table

@node Scratch Variables,  , Input/Output Formats, Variables
@subsection Scratch Variables

Most of the time, variables don't retain their values between cases.
Instead, either they're being read from a data file or the active file,
in which case they assume the value read, or, if created with
@cmd{COMPUTE} or
another transformation, they're initialized to the system-missing value
or to blanks, depending on type.

However, sometimes it's useful to have a variable that keeps its value
between cases.  You can do this with @cmd{LEAVE} (@pxref{LEAVE}), or you can
use a @dfn{scratch variable}.  Scratch variables are variables whose
names begin with an octothorpe (@samp{#}).  

Scratch variables have the same properties as variables left with
@cmd{LEAVE}:
they retain their values between cases, and for the first case they are
initialized to 0 or blanks.  They have the additional property that they
are deleted before the execution of any procedure.  For this reason,
scratch variables can't be used for analysis.  To obtain the same
effect, use @cmd{COMPUTE} (@pxref{COMPUTE}) to copy the scratch variable's
value into an ordinary variable, then analysis that variable.

@node Files, BNF, Variables, Language
@section Files Used by PSPP

PSPP makes use of many files each time it runs.  Some of these it
reads, some it writes, some it creates.  Here is a table listing the
most important of these files:

@table @strong
@cindex file, command
@cindex file, syntax file
@cindex command file
@cindex syntax file
@item command file
@itemx syntax file
These names (synonyms) refer to the file that contains instructions to
PSPP that tell it what to do.  The syntax file's name is specified on
the PSPP command line.  Syntax files can also be pulled in with
@cmd{INCLUDE} (@pxref{INCLUDE}).

@cindex file, data
@cindex data file
@item data file
Data files contain raw data in ASCII format suitable for being read in
by @cmd{DATA LIST}.  Data can be embedded in the syntax
file with @cmd{BEGIN DATA} and @cmd{END DATA}: this makes the
syntax file a data file too.

@cindex file, output
@cindex output file
@item listing file
One or more output files are created by PSPP each time it is
run.  The output files receive the tables and charts produced by
statistical procedures.  The output files may be in any number of formats,
depending on how PSPP is configured.

@cindex active file
@cindex file, active
@item active file
The active file is the ``file'' on which all PSPP procedures
are performed.  The active file contains variable definitions and
cases.  The active file is not necessarily a disk file: it is stored
in memory if there is room.
@end table

@node BNF,  , Files, Language
@section Backus-Naur Form
@cindex BNF
@cindex Backus-Naur Form
@cindex command syntax, description of
@cindex description of command syntax

The syntax of some parts of the PSPP language is presented in this
manual using the formalism known as @dfn{Backus-Naur Form}, or BNF. The
following table describes BNF:

@itemize @bullet
@cindex keywords
@cindex terminals
@item
Words in all-uppercase are PSPP keyword tokens.  In BNF, these are
often called @dfn{terminals}.  There are some special terminals, which
are actually written in lowercase for clarity:

@table @asis
@cindex @code{number}
@item @code{number}
A real number.

@cindex @code{integer}
@item @code{integer}
An integer number.

@cindex @code{string}
@item @code{string}
A string.

@cindex @code{var-name}
@item @code{var-name}
A single variable name.

@cindex operators
@cindex punctuators
@item @code{=}, @code{/}, @code{+}, @code{-}, etc.
Operators and punctuators.

@cindex @code{.}
@cindex terminal dot
@cindex dot, terminal
@item @code{.}
The terminal dot.  This is not necessarily an actual dot in the syntax
file: @xref{Commands}, for more details.
@end table

@item
@cindex productions
@cindex nonterminals
Other words in all lowercase refer to BNF definitions, called
@dfn{productions}.  These productions are also known as
@dfn{nonterminals}.  Some nonterminals are very common, so they are
defined here in English for clarity:

@table @code
@cindex @code{var-list}
@item var-list
A list of one or more variable names or the keyword @code{ALL}.

@cindex @code{expression}
@item expression
An expression.  @xref{Expressions}, for details.
@end table

@item
@cindex @code{::=}
@cindex ``is defined as''
@cindex productions
@samp{::=} means ``is defined as''.  The left side of @samp{::=} gives
the name of the nonterminal being defined.  The right side of @samp{::=}
gives the definition of that nonterminal.  If the right side is empty,
then one possible expansion of that nonterminal is nothing.  A BNF
definition is called a @dfn{production}.

@item
@cindex terminals and nonterminals, differences
So, the key difference between a terminal and a nonterminal is that a
terminal cannot be broken into smaller parts---in fact, every terminal
is a single token (@pxref{Tokens}).  On the other hand, nonterminals are
composed of a (possibly empty) sequence of terminals and nonterminals.
Thus, terminals indicate the deepest level of syntax description.  (In
parsing theory, terminals are the leaves of the parse tree; nonterminals
form the branches.)

@item
@cindex start symbol
@cindex symbol, start
The first nonterminal defined in a set of productions is called the
@dfn{start symbol}.  The start symbol defines the entire syntax for
that command.
@end itemize
@setfilename ignored