2 @chapter The PSPP language
6 This chapter discusses elements common to many PSPP commands.
7 Later chapters will describe individual commands in detail.
10 * Tokens:: Characters combine to form tokens.
11 * Commands:: Tokens combine to form commands.
12 * Syntax Variants:: Batch vs. Interactive mode
13 * Types of Commands:: Commands come in several flavors.
14 * Order of Commands:: Commands combine to form syntax files.
15 * Missing Observations:: Handling missing observations.
16 * Datasets:: Data organization.
17 * Files:: Files used by PSPP.
18 * File Handles:: How files are named.
19 * BNF:: How command syntax is described.
25 @cindex language, lexical analysis
26 @cindex language, tokens
28 @cindex lexical analysis
30 PSPP divides most syntax file lines into series of short chunks
32 Tokens are then grouped to form commands, each of which tells
33 PSPP to take some action---read in data, write out data, perform
34 a statistical procedure, etc. Each type of token is
40 Identifiers are names that typically specify variables, commands, or
41 subcommands. The first character in an identifier must be a letter,
42 @samp{#}, or @samp{@@}. The remaining characters in the identifier
43 must be letters, digits, or one of the following special characters:
49 @cindex case-sensitivity
50 Identifiers may be any length, but only the first 64 bytes are
51 significant. Identifiers are not case-sensitive: @code{foobar},
52 @code{Foobar}, @code{FooBar}, @code{FOOBAR}, and @code{FoObaR} are
53 different representations of the same identifier.
55 @cindex identifiers, reserved
56 @cindex reserved identifiers
57 Some identifiers are reserved. Reserved identifiers may not be used
58 in any context besides those explicitly described in this manual. The
59 reserved identifiers are:
62 @center ALL AND BY EQ GE GT LE LT NE NOT OR TO WITH
66 Keywords are a subclass of identifiers that form a fixed part of
67 command syntax. For example, command and subcommand names are
68 keywords. Keywords may be abbreviated to their first 3 characters if
69 this abbreviation is unambiguous. (Unique abbreviations of 3 or more
70 characters are also accepted: @samp{FRE}, @samp{FREQ}, and
71 @samp{FREQUENCIES} are equivalent when the last is a keyword.)
73 Reserved identifiers are always used as keywords. Other identifiers
74 may be used both as keywords and as user-defined identifiers, such as
81 Numbers are expressed in decimal. A decimal point is optional.
82 Numbers may be expressed in scientific notation by adding @samp{e} and
83 a base-10 exponent, so that @samp{1.234e3} has the value 1234. Here
84 are some more examples of valid numbers:
87 -5 3.14159265359 1e100 -.707 8945.
90 Negative numbers are expressed with a @samp{-} prefix. However, in
91 situations where a literal @samp{-} token is expected, what appears to
92 be a negative number is treated as @samp{-} followed by a positive
95 No white space is allowed within a number token, except for horizontal
96 white space between @samp{-} and the rest of the number.
98 The last example above, @samp{8945.} will be interpreted as two
99 tokens, @samp{8945} and @samp{.}, if it is the last token on a line.
100 @xref{Commands, , Forming commands of tokens}.
106 @cindex case-sensitivity
107 Strings are literal sequences of characters enclosed in pairs of
108 single quotes (@samp{'}) or double quotes (@samp{"}). To include the
109 character used for quoting in the string, double it, e.g.@:
110 @samp{'it''s an apostrophe'}. White space and case of letters are
111 significant inside strings.
113 Strings can be concatenated using @samp{+}, so that @samp{"a" + 'b' +
114 'c'} is equivalent to @samp{'abc'}. So that a long string may be
115 broken across lines, a line break may precede or follow, or both
116 precede and follow, the @samp{+}. (However, an entirely blank line
117 preceding or following the @samp{+} is interpreted as ending the
120 Strings may also be expressed as hexadecimal character values by
121 prefixing the initial quote character by @samp{x} or @samp{X}.
122 Regardless of the syntax file or active dataset's encoding, the
123 hexadecimal digits in the string are interpreted as Unicode characters
126 Individual Unicode code points may also be expressed by specifying the
127 hexadecimal code point number in single or double quotes preceded by
128 @samp{u} or @samp{U}. For example, Unicode code point U+1D11E, the
129 musical G clef character, could be expressed as @code{U'1D11E'}.
130 Invalid Unicode code points (above U+10FFFF or in between U+D800 and
131 U+DFFF) are not allowed.
133 When strings are concatenated with @samp{+}, each segment's prefix is
134 considered individually. For example, @code{'The G clef symbol is:' +
135 u"1d11e" + "."} inserts a G clef symbol in the middle of an otherwise
138 @item Punctuators and Operators
141 These tokens are the punctuators and operators:
144 @center , / = ( ) + - * / ** < <= <> > >= ~= & | .
147 Most of these appear within the syntax of commands, but the period
148 (@samp{.}) punctuator is used only at the end of a command. It is a
149 punctuator only as the last character on a line (except white space).
150 When it is the last non-space character on a line, a period is not
151 treated as part of another token, even if it would otherwise be part
152 of, e.g.@:, an identifier or a floating-point number.
156 @section Forming commands of tokens
158 @cindex PSPP, command structure
159 @cindex language, command structure
160 @cindex commands, structure
162 Most PSPP commands share a common structure. A command begins with a
163 command name, such as @cmd{FREQUENCIES}, @cmd{DATA LIST}, or @cmd{N OF
164 CASES}. The command name may be abbreviated to its first word, and
165 each word in the command name may be abbreviated to its first three
166 or more characters, where these abbreviations are unambiguous.
168 The command name may be followed by one or more @dfn{subcommands}.
169 Each subcommand begins with a subcommand name, which may be
170 abbreviated to its first three letters. Some subcommands accept a
171 series of one or more specifications, which follow the subcommand
172 name, optionally separated from it by an equals sign
173 (@samp{=}). Specifications may be separated from each other
174 by commas or spaces. Each subcommand must be separated from the next (if any)
175 by a forward slash (@samp{/}).
177 There are multiple ways to mark the end of a command. The most common
178 way is to end the last line of the command with a period (@samp{.}) as
179 described in the previous section (@pxref{Tokens}). A blank line, or
180 one that consists only of white space or comments, also ends a command.
182 @node Syntax Variants
183 @section Syntax Variants
186 @cindex Interactive syntax
188 There are three variants of command syntax, which vary only in how
189 they detect the end of one command and the start of the next.
191 In @dfn{interactive mode}, which is the default for syntax typed at a
192 command prompt, a period as the last non-blank character on a line
193 ends a command. A blank line also ends a command.
195 In @dfn{batch mode}, an end-of-line period or a blank line also ends a
196 command. Additionally, it treats any line that has a non-blank
197 character in the leftmost column as beginning a new command. Thus, in
198 batch mode the second and subsequent lines in a command must be
201 Regardless of the syntax mode, a plus sign, minus sign, or period in
202 the leftmost column of a line is ignored and causes that line to begin
203 a new command. This is most useful in batch mode, in which the first
204 line of a new command could not otherwise be indented, but it is
205 accepted regardless of syntax mode.
207 The default mode for reading commands from a file is @dfn{auto mode}.
208 It is the same as batch mode, except that a line with a non-blank in
209 the leftmost column only starts a new command if that line begins with
210 the name of a PSPP command. This correctly interprets most valid PSPP
211 syntax files regardless of the syntax mode for which they are
214 The @option{--interactive} (or @option{-i}) or @option{--batch} (or
215 @option{-b}) options set the syntax mode for files listed on the PSPP
216 command line. @xref{Main Options}, for more details.
218 @node Types of Commands
219 @section Types of Commands
221 Commands in PSPP are divided roughly into six categories:
224 @item Utility commands
225 @cindex utility commands
226 Set or display various global options that affect PSPP operations.
227 May appear anywhere in a syntax file. @xref{Utilities, , Utility
230 @item File definition commands
231 @cindex file definition commands
232 Give instructions for reading data from text files or from special
233 binary ``system files''. Most of these commands replace any previous
234 data or variables with new data or
235 variables. At least one file definition command must appear before the first command in any of
236 the categories below. @xref{Data Input and Output}.
238 @item Input program commands
239 @cindex input program commands
240 Though rarely used, these provide tools for reading data files
241 in arbitrary textual or binary formats. @xref{INPUT PROGRAM}.
243 @item Transformations
244 @cindex transformations
245 Perform operations on data and write data to output files. Transformations
246 are not carried out until a procedure is executed.
248 @item Restricted transformations
249 @cindex restricted transformations
250 Transformations that cannot appear in certain contexts. @xref{Order
251 of Commands}, for details.
255 Analyze data, writing results of analyses to the listing file. Cause
256 transformations specified earlier in the file to be performed. In a
257 more general sense, a @dfn{procedure} is any command that causes the
258 active dataset (the data) to be read.
261 @node Order of Commands
262 @section Order of Commands
263 @cindex commands, ordering
264 @cindex order of commands
266 PSPP does not place many restrictions on ordering of commands. The
267 main restriction is that variables must be defined before they are otherwise
268 referenced. This section describes the details of command ordering,
269 but most users will have no need to refer to them.
271 PSPP possesses five internal states, called initial, INPUT PROGRAM,
272 FILE TYPE, transformation, and procedure states. (Please note the
273 distinction between the @cmd{INPUT PROGRAM} and @cmd{FILE TYPE}
274 @emph{commands} and the INPUT PROGRAM and FILE TYPE @emph{states}.)
276 PSPP starts in the initial state. Each successful completion
277 of a command may cause a state transition. Each type of command has its
278 own rules for state transitions:
281 @item Utility commands
286 Do not cause state transitions. Exception: when @cmd{N OF CASES}
287 is executed in the procedure state, it causes a transition to the
288 transformation state.
291 @item @cmd{DATA LIST}
296 When executed in the initial or procedure state, causes a transition to
297 the transformation state.
299 Clears the active dataset if executed in the procedure or transformation
303 @item @cmd{INPUT PROGRAM}
306 Invalid in INPUT PROGRAM and FILE TYPE states.
308 Causes a transition to the INPUT PROGRAM state.
310 Clears the active dataset.
313 @item @cmd{FILE TYPE}
316 Invalid in INPUT PROGRAM and FILE TYPE states.
318 Causes a transition to the FILE TYPE state.
320 Clears the active dataset.
323 @item Other file definition commands
326 Invalid in INPUT PROGRAM and FILE TYPE states.
328 Cause a transition to the transformation state.
330 Clear the active dataset, except for @cmd{ADD FILES}, @cmd{MATCH FILES},
334 @item Transformations
337 Invalid in initial and FILE TYPE states.
339 Cause a transition to the transformation state.
342 @item Restricted transformations
345 Invalid in initial, INPUT PROGRAM, and FILE TYPE states.
347 Cause a transition to the transformation state.
353 Invalid in initial, INPUT PROGRAM, and FILE TYPE states.
355 Cause a transition to the procedure state.
359 @node Missing Observations
360 @section Handling missing observations
361 @cindex missing values
362 @cindex values, missing
364 PSPP includes special support for unknown numeric data values.
365 Missing observations are assigned a special value, called the
366 @dfn{system-missing value}. This ``value'' actually indicates the
367 absence of a value; it means that the actual value is unknown. Procedures
368 automatically exclude from analyses those observations or cases that
369 have missing values. Details of missing value exclusion depend on the
370 procedure and can often be controlled by the user; refer to
371 descriptions of individual procedures for details.
373 The system-missing value exists only for numeric variables. String
374 variables always have a defined value, even if it is only a string of
377 Variables, whether numeric or string, can have designated
378 @dfn{user-missing values}. Every user-missing value is an actual value
379 for that variable. However, most of the time user-missing values are
380 treated in the same way as the system-missing value.
382 For more information on missing values, see the following sections:
383 @ref{Datasets}, @ref{MISSING VALUES}, @ref{Expressions}. See also the
384 documentation on individual procedures for information on how they
385 handle missing values.
393 PSPP works with data organized into @dfn{datasets}. A dataset
394 consists of a set of @dfn{variables}, which taken together are said to
395 form a @dfn{dictionary}, and one or more @dfn{cases}, each of which
396 has one value for each variable.
398 At any given time PSPP has exactly one distinguished dataset, called
399 the @dfn{active dataset}. Most PSPP commands work only with the
400 active dataset. In addition to the active dataset, PSPP also supports
401 any number of additional open datasets. The @cmd{DATASET} commands
402 can choose a new active dataset from among those that are open, as
403 well as create and destroy datasets (@pxref{DATASET}).
405 The sections below describe variables in more detail.
408 * Attributes:: Attributes of variables.
409 * System Variables:: Variables automatically defined by PSPP.
410 * Sets of Variables:: Lists of variable names.
411 * Input and Output Formats:: Input and output formats.
412 * Scratch Variables:: Variables deleted by procedures.
416 @subsection Attributes of Variables
417 @cindex variables, attributes of
418 @cindex attributes of variables
419 Each variable has a number of attributes, including:
423 An identifier, up to 64 bytes long. Each variable must have a different name.
426 Some system variable names begin with @samp{$}, but user-defined
427 variables' names may not begin with @samp{$}.
431 @cindex variable names, ending with period
432 The final character in a variable name should not be @samp{.}, because
433 such an identifier will be misinterpreted when it is the final token
434 on a line: @code{FOO.} will be divided into two separate tokens,
435 @samp{FOO} and @samp{.}, indicating end-of-command. @xref{Tokens}.
438 The final character in a variable name should not be @samp{_}, because
439 some such identifiers are used for special purposes by PSPP
442 As with all PSPP identifiers, variable names are not case-sensitive.
443 PSPP capitalizes variable names on output the same way they were
444 capitalized at their point of definition in the input.
446 @cindex variables, type
447 @cindex type of variables
451 @cindex variables, width
452 @cindex width of variables
454 (string variables only) String variables with a width of 8 characters or
455 fewer are called @dfn{short string variables}. Short string variables
456 may be used in a few contexts where @dfn{long string variables} (those
457 with widths greater than 8) are not allowed.
460 Variables in the dictionary are arranged in a specific order.
461 @cmd{DISPLAY} can be used to show this order: see @ref{DISPLAY}.
464 Either reinitialized to 0 or spaces for each case, or left at its
465 existing value. @xref{LEAVE}.
467 @cindex missing values
468 @cindex values, missing
470 Optionally, up to three values, or a range of values, or a specific
471 value plus a range, can be specified as @dfn{user-missing values}.
472 There is also a @dfn{system-missing value} that is assigned to an
473 observation when there is no other obvious value for that observation.
474 Observations with missing values are automatically excluded from
475 analyses. User-missing values are actual data values, while the
476 system-missing value is not a value at all. @xref{Missing Observations}.
478 @cindex variable labels
479 @cindex labels, variable
481 A string that describes the variable. @xref{VARIABLE LABELS}.
484 @cindex labels, value
486 Optionally, these associate each possible value of the variable with a
487 string. @xref{VALUE LABELS}.
491 Display width, format, and (for numeric variables) number of decimal
492 places. This attribute does not affect how data are stored, just how
493 they are displayed. Example: a width of 8, with 2 decimal places.
494 @xref{Input and Output Formats}.
498 Similar to print format, but used by the @cmd{WRITE} command
501 @cindex custom attributes
502 @item Custom attributes
503 User-defined associations between names and values. @xref{VARIABLE
507 @node System Variables
508 @subsection Variables Automatically Defined by PSPP
509 @cindex system variables
510 @cindex variables, system
512 There are seven system variables. These are not like ordinary
513 variables because system variables are not always stored. They can be used only
514 in expressions. These system variables, whose values and output formats
515 cannot be modified, are described below.
518 @cindex @code{$CASENUM}
520 Case number of the case at the moment. This changes as cases are
525 Date the PSPP process was started, in format A9, following the
526 pattern @code{DD MMM YY}.
528 @cindex @code{$JDATE}
530 Number of days between 15 Oct 1582 and the time the PSPP process
533 @cindex @code{$LENGTH}
535 Page length, in lines, in format F11.
537 @cindex @code{$SYSMIS}
539 System missing value, in format F1.
543 Number of seconds between midnight 14 Oct 1582 and the time the active dataset
544 was read, in format F20.
546 @cindex @code{$WIDTH}
548 Page width, in characters, in format F3.
551 @node Sets of Variables
552 @subsection Lists of variable names
553 @cindex @code{TO} convention
554 @cindex convention, @code{TO}
556 To refer to a set of variables, list their names one after another.
557 Optionally, their names may be separated by commas. To include a
558 range of variables from the dictionary in the list, write the name of
559 the first and last variable in the range, separated by @code{TO}. For
560 instance, if the dictionary contains six variables with the names
561 @code{ID}, @code{X1}, @code{X2}, @code{GOAL}, @code{MET}, and
562 @code{NEXTGOAL}, in that order, then @code{X2 TO MET} would include
563 variables @code{X2}, @code{GOAL}, and @code{MET}.
565 Commands that define variables, such as @cmd{DATA LIST}, give
566 @code{TO} an alternate meaning. With these commands, @code{TO} define
567 sequences of variables whose names end in consecutive integers. The
568 syntax is two identifiers that begin with the same root and end with
569 numbers, separated by @code{TO}. The syntax @code{X1 TO X5} defines 5
570 variables, named @code{X1}, @code{X2}, @code{X3}, @code{X4}, and
571 @code{X5}. The syntax @code{ITEM0008 TO ITEM0013} defines 6
572 variables, named @code{ITEM0008}, @code{ITEM0009}, @code{ITEM0010},
573 @code{ITEM0011}, @code{ITEM0012}, and @code{ITEM00013}. The syntaxes
574 @code{QUES001 TO QUES9} and @code{QUES6 TO QUES3} are invalid.
576 After a set of variables has been defined with @cmd{DATA LIST} or
577 another command with this method, the same set can be referenced on
578 later commands using the same syntax.
580 @node Input and Output Formats
581 @subsection Input and Output Formats
584 An @dfn{input format} describes how to interpret the contents of an
585 input field as a number or a string. It might specify that the field
586 contains an ordinary decimal number, a time or date, a number in binary
587 or hexadecimal notation, or one of several other notations. Input
588 formats are used by commands such as @cmd{DATA LIST} that read data or
589 syntax files into the PSPP active dataset.
591 Every input format corresponds to a default @dfn{output format} that
592 specifies the formatting used when the value is output later. It is
593 always possible to explicitly specify an output format that resembles
594 the input format. Usually, this is the default, but in cases where the
595 input format is unfriendly to human readability, such as binary or
596 hexadecimal formats, the default output format is an easier-to-read
599 Every variable has two output formats, called its @dfn{print format} and
600 @dfn{write format}. Print formats are used in most output contexts;
601 write formats are used only by @cmd{WRITE} (@pxref{WRITE}). Newly
602 created variables have identical print and write formats, and
603 @cmd{FORMATS}, the most commonly used command for changing formats
604 (@pxref{FORMATS}), sets both of them to the same value as well. Thus,
605 most of the time, the distinction between print and write formats is
608 Input and output formats are specified to PSPP with a @dfn{format
609 specification} of the form @code{TYPEw} or @code{TYPEw.d}, where
610 @code{TYPE} is one of the format types described later, @code{w} is a
611 field width measured in columns, and @code{d} is an optional number of
612 decimal places. If @code{d} is omitted, a value of 0 is assumed. Some
613 formats do not allow a nonzero @code{d} to be specified.
615 The following sections describe the input and output formats supported
619 * Basic Numeric Formats::
620 * Custom Currency Formats::
621 * Legacy Numeric Formats::
622 * Binary and Hexadecimal Numeric Formats::
623 * Time and Date Formats::
624 * Date Component Formats::
628 @node Basic Numeric Formats
629 @subsubsection Basic Numeric Formats
631 @cindex numeric formats
632 The basic numeric formats are used for input and output of real numbers
633 in standard or scientific notation. The following table shows an
634 example of how each format displays positive and negative numbers with
635 the default decimal point setting:
638 @multitable {DOLLAR10.2} {@code{@tie{}$3,141.59}} {@code{-$3,141.59}}
639 @headitem Format @tab @code{@tie{}3141.59} @tab @code{-3141.59}
640 @item F8.2 @tab @code{@tie{}3141.59} @tab @code{-3141.59}
641 @item COMMA9.2 @tab @code{@tie{}3,141.59} @tab @code{-3,141.59}
642 @item DOT9.2 @tab @code{@tie{}3.141,59} @tab @code{-3.141,59}
643 @item DOLLAR10.2 @tab @code{@tie{}$3,141.59} @tab @code{-$3,141.59}
644 @item PCT9.2 @tab @code{@tie{}3141.59%} @tab @code{-3141.59%}
645 @item E8.1 @tab @code{@tie{}3.1E+003} @tab @code{-3.1E+003}
649 On output, numbers in F format are expressed in standard decimal
650 notation with the requested number of decimal places. The other formats
651 output some variation on this style:
655 Numbers in COMMA format are additionally grouped every three digits by
656 inserting a grouping character. The grouping character is ordinarily a
657 comma, but it can be changed to a period (@pxref{SET DECIMAL}).
660 DOT format is like COMMA format, but it interchanges the role of the
661 decimal point and grouping characters. That is, the current grouping
662 character is used as a decimal point and vice versa.
665 DOLLAR format is like COMMA format, but it prefixes the number with
669 PCT format is like F format, but adds @samp{%} after the number.
672 The E format always produces output in scientific notation.
675 On input, the basic numeric formats accept positive and numbers in
676 standard decimal notation or scientific notation. Leading and trailing
677 spaces are allowed. An empty or all-spaces field, or one that contains
678 only a single period, is treated as the system missing value.
680 In scientific notation, the exponent may be introduced by a sign
681 (@samp{+} or @samp{-}), or by one of the letters @samp{e} or @samp{d}
682 (in uppercase or lowercase), or by a letter followed by a sign. A
683 single space may follow the letter or the sign or both.
685 On fixed-format @cmd{DATA LIST} (@pxref{DATA LIST FIXED}) and in a few
686 other contexts, decimals are implied when the field does not contain a
687 decimal point. In F6.5 format, for example, the field @code{314159} is
688 taken as the value 3.14159 with implied decimals. Decimals are never
689 implied if an explicit decimal point is present or if scientific
692 E and F formats accept the basic syntax already described. The other
693 formats allow some additional variations:
697 COMMA, DOLLAR, and DOT formats ignore grouping characters within the
698 integer part of the input field. The identity of the grouping
699 character depends on the format.
702 DOLLAR format allows a dollar sign to precede the number. In a negative
703 number, the dollar sign may precede or follow the minus sign.
706 PCT format allows a percent sign to follow the number.
709 All of the basic number formats have a maximum field width of 40 and
710 accept no more than 16 decimal places, on both input and output. Some
711 additional restrictions apply:
715 As input formats, the basic numeric formats allow no more decimal places
716 than the field width. As output formats, the field width must be
717 greater than the number of decimal places; that is, large enough to
718 allow for a decimal point and the number of requested decimal places.
719 DOLLAR and PCT formats must allow an additional column for @samp{$} or
723 The default output format for a given input format increases the field
724 width enough to make room for optional input characters. If an input
725 format calls for decimal places, the width is increased by 1 to make
726 room for an implied decimal point. COMMA, DOT, and DOLLAR formats also
727 increase the output width to make room for grouping characters. DOLLAR
728 and PCT further increase the output field width by 1 to make room for
729 @samp{$} or @samp{%}. The increased output width is capped at 40, the
733 The E format is exceptional. For output, E format has a minimum width
734 of 7 plus the number of decimal places. The default output format for
735 an E input format is an E format with at least 3 decimal places and
736 thus a minimum width of 10.
739 More details of basic numeric output formatting are given below:
743 Output rounds to nearest, with ties rounded away from zero. Thus, 2.5
744 is output as @code{3} in F1.0 format, and -1.125 as @code{-1.13} in F5.1
748 The system-missing value is output as a period in a field of spaces,
749 placed in the decimal point's position, or in the rightmost column if no
750 decimal places are requested. A period is used even if the decimal
751 point character is a comma.
754 A number that does not fill its field is right-justified within the
758 A number is too large for its field causes decimal places to be dropped
759 to make room. If dropping decimals does not make enough room,
760 scientific notation is used if the field is wide enough. If a number
761 does not fit in the field, even in scientific notation, the overflow is
762 indicated by filling the field with asterisks (@samp{*}).
765 COMMA, DOT, and DOLLAR formats insert grouping characters only if space
766 is available for all of them. Grouping characters are never inserted
767 when all decimal places must be dropped. Thus, 1234.56 in COMMA5.2
768 format is output as @samp{@tie{}1235} without a comma, even though there
769 is room for one, because all decimal places were dropped.
772 DOLLAR or PCT format drop the @samp{$} or @samp{%} only if the number
773 would not fit at all without it. Scientific notation with @samp{$} or
774 @samp{%} is preferred to ordinary decimal notation without it.
777 Except in scientific notation, a decimal point is included only when
778 it is followed by a digit. If the integer part of the number being
779 output is 0, and a decimal point is included, then the zero before the
780 decimal point is dropped.
782 In scientific notation, the number always includes a decimal point,
783 even if it is not followed by a digit.
786 A negative number includes a minus sign only in the presence of a
787 nonzero digit: -0.01 is output as @samp{-.01} in F4.2 format but as
788 @samp{@tie{}@tie{}.0} in F4.1 format. Thus, a ``negative zero'' never
789 includes a minus sign.
792 In negative numbers output in DOLLAR format, the dollar sign follows the
793 negative sign. Thus, -9.99 in DOLLAR6.2 format is output as
797 In scientific notation, the exponent is output as @samp{E} followed by
798 @samp{+} or @samp{-} and exactly three digits. Numbers with magnitude
799 less than 10**-999 or larger than 10**999 are not supported by most
800 computers, but if they are supported then their output is considered
801 to overflow the field and will be output as asterisks.
804 On most computers, no more than 15 decimal digits are significant in
805 output, even if more are printed. In any case, output precision cannot
806 be any higher than input precision; few data sets are accurate to 15
807 digits of precision. Unavoidable loss of precision in intermediate
808 calculations may also reduce precision of output.
811 Special values such as infinities and ``not a number'' values are
812 usually converted to the system-missing value before printing. In a few
813 circumstances, these values are output directly. In fields of width 3
814 or greater, special values are output as however many characters will
815 fit from @code{+Infinity} or @code{-Infinity} for infinities, from
816 @code{NaN} for ``not a number,'' or from @code{Unknown} for other values
817 (if any are supported by the system). In fields under 3 columns wide,
818 special values are output as asterisks.
821 @node Custom Currency Formats
822 @subsubsection Custom Currency Formats
824 @cindex currency formats
825 The custom currency formats are closely related to the basic numeric
826 formats, but they allow users to customize the output format. The
827 SET command configures custom currency formats, using the syntax
829 SET CC@var{x}=@t{"}@var{string}@t{"}.
832 where @var{x} is A, B, C, D, or E, and @var{string} is no more than 16
835 @var{string} must contain exactly three commas or exactly three periods
836 (but not both), except that a single quote character may be used to
837 ``escape'' a following comma, period, or single quote. If three commas
838 are used, commas will be used for grouping in output, and a period will
839 be used as the decimal point. Uses of periods reverses these roles.
841 The commas or periods divide @var{string} into four fields, called the
842 @dfn{negative prefix}, @dfn{prefix}, @dfn{suffix}, and @dfn{negative
843 suffix}, respectively. The prefix and suffix are added to output
844 whenever space is available. The negative prefix and negative suffix
845 are always added to a negative number when the output includes a nonzero
848 The following syntax shows how custom currency formats could be used to
849 reproduce basic numeric formats:
853 SET CCA="-,,,". /* Same as COMMA.
854 SET CCB="-...". /* Same as DOT.
855 SET CCC="-,$,,". /* Same as DOLLAR.
856 SET CCD="-,,%,". /* Like PCT, but groups with commas.
860 Here are some more examples of custom currency formats. The final
861 example shows how to use a single quote to escape a delimiter:
865 SET CCA=",EUR,,-". /* Euro.
866 SET CCB="(,USD ,,)". /* US dollar.
867 SET CCC="-.R$..". /* Brazilian real.
868 SET CCD="-,, NIS,". /* Israel shekel.
869 SET CCE="-.Rp'. ..". /* Indonesia Rupiah.
873 @noindent These formats would yield the following output:
876 @multitable {CCD13.2} {@code{@tie{}@tie{}USD 3,145.59}} {@code{(USD 3,145.59)}}
877 @headitem Format @tab @code{@tie{}3145.59} @tab @code{-3145.59}
878 @item CCA12.2 @tab @code{@tie{}EUR3,145.59} @tab @code{EUR3,145.59-}
879 @item CCB14.2 @tab @code{@tie{}@tie{}USD 3,145.59} @tab @code{(USD 3,145.59)}
880 @item CCC11.2 @tab @code{@tie{}R$3.145,59} @tab @code{-R$3.145,59}
881 @item CCD13.2 @tab @code{@tie{}3,145.59 NIS} @tab @code{-3,145.59 NIS}
882 @item CCE10.0 @tab @code{@tie{}Rp. 3.146} @tab @code{-Rp. 3.146}
886 The default for all the custom currency formats is @samp{-,,,},
887 equivalent to COMMA format.
889 @node Legacy Numeric Formats
890 @subsubsection Legacy Numeric Formats
892 The N and Z numeric formats provide compatibility with legacy file
893 formats. They have much in common:
897 Output is rounded to the nearest representable value, with ties rounded
901 Numbers too large to display are output as a field filled with asterisks
905 The decimal point is always implicitly the specified number of digits
906 from the right edge of the field, except that Z format input allows an
907 explicit decimal point.
910 Scientific notation may not be used.
913 The system-missing value is output as a period in a field of spaces.
914 The period is placed just to the right of the implied decimal point in
915 Z format, or at the right end in N format or in Z format if no decimal
916 places are requested. A period is used even if the decimal point
917 character is a comma.
920 Field width may range from 1 to 40. Decimal places may range from 0 up
921 to the field width, to a maximum of 16.
924 When a legacy numeric format used for input is converted to an output
925 format, it is changed into the equivalent F format. The field width is
926 increased by 1 if any decimal places are specified, to make room for a
927 decimal point. For Z format, the field width is increased by 1 more
928 column, to make room for a negative sign. The output field width is
929 capped at 40 columns.
932 @subsubheading N Format
934 The N format supports input and output of fields that contain only
935 digits. On input, leading or trailing spaces, a decimal point, or any
936 other non-digit character causes the field to be read as the
937 system-missing value. As a special exception, an N format used on
938 @cmd{DATA LIST FREE} or @cmd{DATA LIST LIST} is treated as the
941 On output, N pads the field on the left with zeros. Negative numbers
942 are output like the system-missing value.
944 @subsubheading Z Format
946 The Z format is a ``zoned decimal'' format used on IBM mainframes. Z
947 format encodes the sign as part of the final digit, which must be one of
955 where the characters in each row represent digits 0 through 9 in order.
956 Characters in the first two rows indicate a positive sign; those in the
957 third indicate a negative sign.
959 On output, Z fields are padded on the left with spaces. On input,
960 leading and trailing spaces are ignored. Any character in an input
961 field other than spaces, the digit characters above, and @samp{.} causes
962 the field to be read as system-missing.
964 The decimal point character for input and output is always @samp{.},
965 even if the decimal point character is a comma (@pxref{SET DECIMAL}).
967 Nonzero, negative values output in Z format are marked as negative even
968 when no nonzero digits are output. For example, -0.2 is output in Z1.0
969 format as @samp{J}. The ``negative zero'' value supported by most
970 machines is output as positive.
972 @node Binary and Hexadecimal Numeric Formats
973 @subsubsection Binary and Hexadecimal Numeric Formats
975 @cindex binary formats
976 @cindex hexadecimal formats
977 The binary and hexadecimal formats are primarily designed for
978 compatibility with existing machine formats, not for human readability.
979 All of them therefore have a F format as default output format. Some of
980 these formats are only portable between machines with compatible byte
981 ordering (endianness) or floating-point format.
983 Binary formats use byte values that in text files are interpreted as
984 special control functions, such as carriage return and line feed. Thus,
985 data in binary formats should not be included in syntax files or read
986 from data files with variable-length records, such as ordinary text
987 files. They may be read from or written to data files with fixed-length
988 records. @xref{FILE HANDLE}, for information on working with
989 fixed-length records.
991 @subsubheading P and PK Formats
993 These are binary-coded decimal formats, in which every byte (except the
994 last, in P format) represents two decimal digits. The most-significant
995 4 bits of the first byte is the most-significant decimal digit, the
996 least-significant 4 bits of the first byte is the next decimal digit,
999 In P format, the most-significant 4 bits of the last byte are the
1000 least-significant decimal digit. The least-significant 4 bits represent
1001 the sign: decimal 15 indicates a negative value, decimal 13 indicates a
1004 Numbers are rounded downward on output. The system-missing value and
1005 numbers outside representable range are output as zero.
1007 The maximum field width is 16. Decimal places may range from 0 up to
1008 the number of decimal digits represented by the field.
1010 The default output format is an F format with twice the input field
1011 width, plus one column for a decimal point (if decimal places were
1014 @subsubheading IB and PIB Formats
1016 These are integer binary formats. IB reads and writes 2's complement
1017 binary integers, and PIB reads and writes unsigned binary integers. The
1018 byte ordering is by default the host machine's, but SET RIB may be used
1019 to select a specific byte ordering for reading (@pxref{SET RIB}) and
1020 SET WIB, similarly, for writing (@pxref{SET WIB}).
1022 The maximum field width is 8. Decimal places may range from 0 up to the
1023 number of decimal digits in the largest value representable in the field
1026 The default output format is an F format whose width is the number of
1027 decimal digits in the largest value representable in the field width,
1028 plus 1 if the format has decimal places.
1030 @subsubheading RB Format
1032 This is a binary format for real numbers. By default it reads and
1033 writes the host machine's floating-point format, but SET RRB may be
1034 used to select an alternate floating-point format for reading
1035 (@pxref{SET RRB}) and SET WRB, similarly, for writing (@pxref{SET
1038 The recommended field width depends on the floating-point format.
1039 NATIVE (the default format), IDL, IDB, VD, VG, and ZL formats should use
1040 a field width of 8. ISL, ISB, VF, and ZS formats should use a field
1041 width of 4. Other field widths will not produce useful results. The
1042 maximum field width is 8. No decimal places may be specified.
1044 The default output format is F8.2.
1046 @subsubheading PIBHEX and RBHEX Formats
1048 These are hexadecimal formats, for reading and writing binary formats
1049 where each byte has been recoded as a pair of hexadecimal digits.
1051 A hexadecimal field consists solely of hexadecimal digits
1052 @samp{0}@dots{}@samp{9} and @samp{A}@dots{}@samp{F}. Uppercase and
1053 lowercase are accepted on input; output is in uppercase.
1055 Other than the hexadecimal representation, these formats are equivalent
1056 to PIB and RB formats, respectively. However, bytes in PIBHEX format
1057 are always ordered with the most-significant byte first (big-endian
1058 order), regardless of the host machine's native byte order or PSPP
1061 Field widths must be even and between 2 and 16. RBHEX format allows no
1062 decimal places; PIBHEX allows as many decimal places as a PIB format
1063 with half the given width.
1065 @node Time and Date Formats
1066 @subsubsection Time and Date Formats
1068 @cindex time formats
1069 @cindex date formats
1070 In PSPP, a @dfn{time} is an interval. The time formats translate
1071 between human-friendly descriptions of time intervals and PSPP's
1072 internal representation of time intervals, which is simply the number of
1073 seconds in the interval. PSPP has two time formats:
1076 @multitable {Time Format} {@code{dd-mmm-yyyy HH:MM:SS.ss}} {@code{01-OCT-1978 04:31:17.01}}
1077 @headitem Time Format @tab Template @tab Example
1078 @item TIME @tab @code{hh:MM:SS.ss} @tab @code{04:31:17.01}
1079 @item DTIME @tab @code{DD HH:MM:SS.ss} @tab @code{00 04:31:17.01}
1083 A @dfn{date} is a moment in the past or the future. Internally, PSPP
1084 represents a date as the number of seconds since the @dfn{epoch},
1085 midnight, Oct. 14, 1582. The date formats translate between
1086 human-readable dates and PSPP's numeric representation of dates and
1087 times. PSPP has several date formats:
1090 @multitable {Date Format} {@code{dd-mmm-yyyy HH:MM:SS.ss}} {@code{01-OCT-1978 04:31:17.01}}
1091 @headitem Date Format @tab Template @tab Example
1092 @item DATE @tab @code{dd-mmm-yyyy} @tab @code{01-OCT-1978}
1093 @item ADATE @tab @code{mm/dd/yyyy} @tab @code{10/01/1978}
1094 @item EDATE @tab @code{dd.mm.yyyy} @tab @code{01.10.1978}
1095 @item JDATE @tab @code{yyyyjjj} @tab @code{1978274}
1096 @item SDATE @tab @code{yyyy/mm/dd} @tab @code{1978/10/01}
1097 @item QYR @tab @code{q Q yyyy} @tab @code{3 Q 1978}
1098 @item MOYR @tab @code{mmm yyyy} @tab @code{OCT 1978}
1099 @item WKYR @tab @code{ww WK yyyy} @tab @code{40 WK 1978}
1100 @item DATETIME @tab @code{dd-mmm-yyyy HH:MM:SS.ss} @tab @code{01-OCT-1978 04:31:17.01}
1104 The templates in the preceding tables describe how the time and date
1105 formats are input and output:
1109 Day of month, from 1 to 31. Always output as two digits.
1113 Month. In output, @code{mm} is output as two digits, @code{mmm} as the
1114 first three letters of an English month name (January, February,
1115 @dots{}). In input, both of these formats, plus Roman numerals, are
1119 Year. In output, DATETIME always produces a 4-digit year; other
1120 formats can produce a 2- or 4-digit year. The century assumed for
1121 2-digit years depends on the EPOCH setting (@pxref{SET EPOCH}). In
1122 output, a year outside the epoch causes the whole field to be filled
1123 with asterisks (@samp{*}).
1126 Day of year (Julian day), from 1 to 366. This is exactly three digits
1127 giving the count of days from the start of the year. January 1 is
1131 Quarter of year, from 1 to 4. Quarters start on January 1, April 1,
1132 July 1, and October 1.
1135 Week of year, from 1 to 53. Output as exactly two digits. January 1 is
1136 the first day of week 1.
1139 Count of days, which may be positive or negative. Output as at least
1143 Count of hours, which may be positive or negative. Output as at least
1147 Hour of day, from 0 to 23. Output as exactly two digits.
1150 Minute of hour, from 0 to 59. Output as exactly two digits.
1153 Seconds within minute, from 0 to 59. The integer part is output as
1154 exactly two digits. On output, seconds and fractional seconds may or
1155 may not be included, depending on field width and decimal places. On
1156 input, seconds and fractional seconds are optional. The DECIMAL setting
1157 controls the character accepted and displayed as the decimal point
1158 (@pxref{SET DECIMAL}).
1161 For output, the date and time formats use the delimiters indicated in
1162 the table. For input, date components may be separated by spaces or by
1163 one of the characters @samp{-}, @samp{/}, @samp{.}, or @samp{,}, and
1164 time components may be separated by spaces, @samp{:}, or @samp{.}. On
1165 input, the @samp{Q} separating quarter from year and the @samp{WK}
1166 separating week from year may be uppercase or lowercase, and the spaces
1167 around them are optional.
1169 On input, all time and date formats accept any amount of leading and
1170 trailing white space.
1172 The maximum width for time and date formats is 40 columns. Minimum
1173 input and output width for each of the time and date formats is shown
1177 @multitable {DATETIME} {Min. Input Width} {Min. Output Width} {4-digit year}
1178 @headitem Format @tab Min. Input Width @tab Min. Output Width @tab Option
1179 @item DATE @tab 8 @tab 9 @tab 4-digit year
1180 @item ADATE @tab 8 @tab 8 @tab 4-digit year
1181 @item EDATE @tab 8 @tab 8 @tab 4-digit year
1182 @item JDATE @tab 5 @tab 5 @tab 4-digit year
1183 @item SDATE @tab 8 @tab 8 @tab 4-digit year
1184 @item QYR @tab 4 @tab 6 @tab 4-digit year
1185 @item MOYR @tab 6 @tab 6 @tab 4-digit year
1186 @item WKYR @tab 6 @tab 8 @tab 4-digit year
1187 @item DATETIME @tab 17 @tab 17 @tab seconds
1188 @item TIME @tab 5 @tab 5 @tab seconds
1189 @item DTIME @tab 8 @tab 8 @tab seconds
1193 In the table, ``Option'' describes what increased output width enables:
1197 A field 2 columns wider than minimum will include a 4-digit year.
1198 (DATETIME format always includes a 4-digit year.)
1201 A field 3 columns wider than minimum will include seconds as well as
1202 minutes. A field 5 columns wider than minimum, or more, can also
1203 include a decimal point and fractional seconds (but no more than allowed
1204 by the format's decimal places).
1207 For the time and date formats, the default output format is the same as
1208 the input format, except that PSPP increases the field width, if
1209 necessary, to the minimum allowed for output.
1211 Time or dates narrower than the field width are right-justified within
1214 When a time or date exceeds the field width, characters are trimmed from
1215 the end until it fits. This can occur in an unusual situation, e.g.@:
1216 with a year greater than 9999 (which adds an extra digit), or for a
1217 negative value on TIME or DTIME (which adds a leading minus sign).
1219 @c What about out-of-range values?
1221 The system-missing value is output as a period at the right end of the
1224 @node Date Component Formats
1225 @subsubsection Date Component Formats
1227 The WKDAY and MONTH formats provide input and output for the names of
1228 weekdays and months, respectively.
1230 On output, these formats convert a number between 1 and 7, for WKDAY, or
1231 between 1 and 12, for MONTH, into the English name of a day or month,
1232 respectively. If the name is longer than the field, it is trimmed to
1233 fit. If the name is shorter than the field, it is padded on the right
1234 with spaces. Values outside the valid range, and the system-missing
1235 value, are output as all spaces.
1237 On input, English weekday or month names (in uppercase or lowercase) are
1238 converted back to their corresponding numbers. Weekday and month names
1239 may be abbreviated to their first 2 or 3 letters, respectively.
1241 The field width may range from 2 to 40, for WKDAY, or from 3 to 40, for
1242 MONTH. No decimal places are allowed.
1244 The default output format is the same as the input format.
1246 @node String Formats
1247 @subsubsection String Formats
1249 @cindex string formats
1250 The A and AHEX formats are the only ones that may be assigned to string
1251 variables. Neither format allows any decimal places.
1253 In A format, the entire field is treated as a string value. The field
1254 width may range from 1 to 32,767, the maximum string width. The default
1255 output format is the same as the input format.
1257 In AHEX format, the field is composed of characters in a string encoded
1258 as hex digit pairs. On output, hex digits are output in uppercase; on
1259 input, uppercase and lowercase are both accepted. The default output
1260 format is A format with half the input width.
1262 @node Scratch Variables
1263 @subsection Scratch Variables
1265 @cindex scratch variables
1266 Most of the time, variables don't retain their values between cases.
1267 Instead, either they're being read from a data file or the active dataset,
1268 in which case they assume the value read, or, if created with
1270 another transformation, they're initialized to the system-missing value
1271 or to blanks, depending on type.
1273 However, sometimes it's useful to have a variable that keeps its value
1274 between cases. You can do this with @cmd{LEAVE} (@pxref{LEAVE}), or you can
1275 use a @dfn{scratch variable}. Scratch variables are variables whose
1276 names begin with an octothorpe (@samp{#}).
1278 Scratch variables have the same properties as variables left with
1279 @cmd{LEAVE}: they retain their values between cases, and for the first
1280 case they are initialized to 0 or blanks. They have the additional
1281 property that they are deleted before the execution of any procedure.
1282 For this reason, scratch variables can't be used for analysis. To use
1283 a scratch variable in an analysis, use @cmd{COMPUTE} (@pxref{COMPUTE})
1284 to copy its value into an ordinary variable, then use that ordinary
1285 variable in the analysis.
1288 @section Files Used by PSPP
1290 PSPP makes use of many files each time it runs. Some of these it
1291 reads, some it writes, some it creates. Here is a table listing the
1292 most important of these files:
1295 @cindex file, command
1296 @cindex file, syntax file
1297 @cindex command file
1301 These names (synonyms) refer to the file that contains instructions
1302 that tell PSPP what to do. The syntax file's name is specified on
1303 the PSPP command line. Syntax files can also be read with
1304 @cmd{INCLUDE} (@pxref{INCLUDE}).
1309 Data files contain raw data in text or binary format. Data can also
1310 be embedded in a syntax file with @cmd{BEGIN DATA} and @cmd{END DATA}.
1312 @cindex file, output
1315 One or more output files are created by PSPP each time it is
1316 run. The output files receive the tables and charts produced by
1317 statistical procedures. The output files may be in any number of formats,
1318 depending on how PSPP is configured.
1321 @cindex file, system
1323 System files are binary files that store a dictionary and a set of
1324 cases. @cmd{GET} and @cmd{SAVE} read and write system files.
1326 @cindex portable file
1327 @cindex file, portable
1329 Portable files are files in a text-based format that store a dictionary
1330 and a set of cases. @cmd{IMPORT} and @cmd{EXPORT} read and write
1335 @section File Handles
1336 @cindex file handles
1338 A @dfn{file handle} is a reference to a data file, system file, or
1339 portable file. Most often, a file handle is specified as the
1340 name of a file as a string, that is, enclosed within @samp{'} or
1343 A file name string that begins or ends with @samp{|} is treated as the
1344 name of a command to pipe data to or from. You can use this feature
1345 to read data over the network using a program such as @samp{curl}
1346 (e.g.@: @code{GET '|curl -s -S http://example.com/mydata.sav'}), to
1347 read compressed data from a file using a program such as @samp{zcat}
1348 (e.g.@: @code{GET '|zcat mydata.sav.gz'}), and for many other
1351 PSPP also supports declaring named file handles with the @cmd{FILE
1352 HANDLE} command. This command associates an identifier of your choice
1353 (the file handle's name) with a file. Later, the file handle name can
1354 be substituted for the name of the file. When PSPP syntax accesses a
1355 file multiple times, declaring a named file handle simplifies updating
1356 the syntax later to use a different file. Use of @cmd{FILE HANDLE} is
1357 also required to read data files in binary formats. @xref{FILE HANDLE},
1358 for more information.
1360 In some circumstances, PSPP must distinguish whether a file handle
1361 refers to a system file or a portable file. When this is necessary to
1362 read a file, e.g.@: as an input file for @cmd{GET} or @cmd{MATCH FILES},
1363 PSPP uses the file's contents to decide. In the context of writing a
1364 file, e.g.@: as an output file for @cmd{SAVE} or @cmd{AGGREGATE}, PSPP
1365 decides based on the file's name: if it ends in @samp{.por} (with any
1366 capitalization), then PSPP writes a portable file; otherwise, PSPP
1367 writes a system file.
1369 INLINE is reserved as a file handle name. It refers to the ``data
1370 file'' embedded into the syntax file between @cmd{BEGIN DATA} and
1371 @cmd{END DATA}. @xref{BEGIN DATA}, for more information.
1373 The file to which a file handle refers may be reassigned on a later
1374 @cmd{FILE HANDLE} command if it is first closed using @cmd{CLOSE FILE
1375 HANDLE}. @xref{CLOSE FILE HANDLE}, for
1379 @section Backus-Naur Form
1381 @cindex Backus-Naur Form
1382 @cindex command syntax, description of
1383 @cindex description of command syntax
1385 The syntax of some parts of the PSPP language is presented in this
1386 manual using the formalism known as @dfn{Backus-Naur Form}, or BNF. The
1387 following table describes BNF:
1393 Words in all-uppercase are PSPP keyword tokens. In BNF, these are
1394 often called @dfn{terminals}. There are some special terminals, which
1395 are written in lowercase for clarity:
1398 @cindex @code{number}
1402 @cindex @code{integer}
1403 @item @code{integer}
1406 @cindex @code{string}
1410 @cindex @code{var-name}
1411 @item @code{var-name}
1412 A single variable name.
1416 @item @code{=}, @code{/}, @code{+}, @code{-}, etc.
1417 Operators and punctuators.
1421 The end of the command. This is not necessarily an actual dot in the
1422 syntax file: @xref{Commands}, for more details.
1427 @cindex nonterminals
1428 Other words in all lowercase refer to BNF definitions, called
1429 @dfn{productions}. These productions are also known as
1430 @dfn{nonterminals}. Some nonterminals are very common, so they are
1431 defined here in English for clarity:
1434 @cindex @code{var-list}
1436 A list of one or more variable names or the keyword @code{ALL}.
1438 @cindex @code{expression}
1440 An expression. @xref{Expressions}, for details.
1444 @cindex ``is defined as''
1446 @samp{::=} means ``is defined as''. The left side of @samp{::=} gives
1447 the name of the nonterminal being defined. The right side of @samp{::=}
1448 gives the definition of that nonterminal. If the right side is empty,
1449 then one possible expansion of that nonterminal is nothing. A BNF
1450 definition is called a @dfn{production}.
1453 @cindex terminals and nonterminals, differences
1454 So, the key difference between a terminal and a nonterminal is that a
1455 terminal cannot be broken into smaller parts---in fact, every terminal
1456 is a single token (@pxref{Tokens}). On the other hand, nonterminals are
1457 composed of a (possibly empty) sequence of terminals and nonterminals.
1458 Thus, terminals indicate the deepest level of syntax description. (In
1459 parsing theory, terminals are the leaves of the parse tree; nonterminals
1463 @cindex start symbol
1464 @cindex symbol, start
1465 The first nonterminal defined in a set of productions is called the
1466 @dfn{start symbol}. The start symbol defines the entire syntax for