@node Glossary, Commands, Keywords, Top
@chapter Glossary of Terms used in this Manual
@findex glossary

@table @dfn
@item .sm
See Environment File.

@item Environment File
When you start SM it looks in a file
(by default called @file{.sm}) to discover where to find files that it
needs (such as the default macros, the help files, and the font files).
You can access variables stored in the environment file yourself,
although this is probably seldom done by non-gurus. For more details,
@pxref{Environment Variables}.

@item Expression
An SM expression is something that can appear on the right hand side of
a @code{SET} command. More specifically, it is something that can appear
as @emph{part} of the right hand side of a @code{SET} command (this
excludes implied do loops: @code{SET x=1,10,2}).  Expressions may also
appear in other contexts, such as in the @code{ANGLE} command, or in
@code{DEFINE name ( @r{expression} )}. A formal definition of an
expression is given by the YACC grammar in @file{control.y} as the
non-terminal symbol @code{expr}.

@item Filecap
Binary files produced by different programmes (and
languages, and even compilers) are not identical, Fortran
`unformatted' files being a glaring example. A filecap file is a
database used to describe the byte-by-byte format of binary files, to
allow SM to read them (using the @code{IMAGE} command).

@item Graphcap
There are a very large range of graphics terminals
(and laser printers and so forth) in this world, and each seems to
have its own set of commands. A graphcap
file is a database that is able to describe (almost) all of these
dialects, allowing SM to plot on a wide range of devices

@item History
SM remembers commands as you type them, so that you
can repeat them or modify them (which includes correcting mistakes).
The set of remembered commands is referred to as the history buffer.

@item List
The word @code{list} is used in a few places in the manual
in the specific sense defined by the YACC grammar in @file{control.y}. A
list is simply a list of words or numbers, and its meaning depends on
the context. For example, @code{SET x=3*@{1 2 3@}} will set the vector
@code{x} to be @code{2 4 6}, while @code{MACRO hi @{ echo Hello@}} will
define the macro @code{hi}.

@item Macro
A macro is an abbreviation for a set of commands, so
instead of typing a complicated sequence of commands you can simply
type the macro's name. You can either think of macros as a new commands in
their own right or as subroutines.

@item Mongo
Mongo is a plotting package written by John Tonry, and
widely used in astronomy 
departments. SM's command language was based on Mongo's, and we have
provided some support for an easy transition from Mongo to SM.

@item p_expr
A parenthesised expression. Many commands expect to be passed the name of
a vector, but will accept an expression in parentheses; for example
in the command @code{POINTS x (y + 2/z)}, @code{(y + 2/z)} is a p_expr.
@findex parenthesised expression

@item s_expr
A scalar expression. This is a term used in some of the command descriptions;
examples would be @code{210157}, @code{x[12]}, or @code{x}. In the latter
case, the first element of the vector @code{x} would be used, so it is
equivalent to @code{x[0]}.

@item Stdgraph
SM uses the stdgraph device driver for most devices, using the information
in the graphcap file (@pxref{Graphcap}).

@item String
A string to SM is a sequence of characters enclosed in single quotes:
@code{'This is a string'}. Strings are primarily used in vector expressions,
but are also used in a few other places (e.g. to specify a format for a
@code{PRINT} or @code{READ} command). Note that characters in double quotes
are @emph{not} strings to SM, merely characters protected from variable
expansion.

@item Termcap
Terminals come in many, many, flavours and types.
Their peculiarities are described by a termcap file, allowing
SM's command editor to run on (almost) any terminal.

@item @TeX{}
@TeX{} is a typesetting language developed by
Donald Knuth. We provide an emulation of certain parts of @TeX{}'s
mathematics mode in SM's label commands.

@item Overload
A keyword (such as @code{DEFINE} or @code{SET}) is said
to be @emph{overload}ed if its meaning has been changed. Usually this
will be by adding functionality, rather than by actually changing what
it does.

@item Variable
A variable is an abbreviation for a sequence of characters, and may
appear anywhere that the characters in question could appear. Even if the
variable contains a number (e.g. @code{6.62559e-34}) it is still just
a characters, although SM may choose to treat them as a number in
some contexts (e.g. the right-hand side of a @code{SET} command).

@item Vector
A set of one (actually, zero) or more elements. The
elements can be either numerical (floating point) or strings. Vectors
are SM's primary data type. Do not confuse a 1-element vector (a scalar)
with a variable (@pxref{Variables}).

@item YACC
The SM command language is written in a language called
YACC (which is supported on Unix systems). We have provided an
implementation of YACC called Bison in the SM distribution.
@end table