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@finalout
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-@comment $Id: scheme.texinfo,v 1.113 2002/02/12 21:50:12 cph Exp $
+@comment $Id: scheme.texinfo,v 1.114 2002/02/13 01:00:56 cph Exp $
@comment %**start of header (This is for running Texinfo on a region.)
@setfilename scheme.info
@settitle MIT Scheme Reference
(@pxref{Internal Definitions}) also extend an environment. (Actually,
all the constructs that extend environments can be expressed in terms of
procedure calls, so there is really just one fundamental mechanism for
-environment extension.)
-A top-level definition (@pxref{Top-Level Definitions}) may add a binding to an existing environment.
+environment extension.) A top-level definition (@pxref{Top-Level
+Definitions}) may add a binding to an existing environment.
@node Initial and Current Environments, Static Scoping, Environment Concepts, Scheme Concepts
@subsection Initial and Current Environments
@findex user-initial-environment
@findex ge
The environment in effect at some point in a program is called the
-@dfn{current environment} at that point. In particular, every @sc{rep}
-loop has a current environment. (@sc{rep} stands for
-``read-eval-print''; the @sc{rep} loop is the Scheme program that reads
-your input, evaluates it, and prints the result.) The environment of
-the top-level @sc{rep} loop (the one you are in when Scheme starts up)
-starts as @code{user-initial-environment}, although it can be changed by
-the @code{ge} procedure. When a new @sc{rep} loop is created, its
-environment is determined by the program that creates it.
+@dfn{current environment} at that point. In particular, every
+@acronym{REP} loop has a current environment. (@acronym{REP} stands for
+``read-eval-print''; the @acronym{REP} loop is the Scheme program that
+reads your input, evaluates it, and prints the result.) The environment
+of the top-level @acronym{REP} loop (the one you are in when Scheme
+starts up) starts as @code{user-initial-environment}, although it can be
+changed by the @code{ge} procedure. When a new @acronym{REP} loop is
+created, its environment is determined by the program that creates it.
@node Static Scoping, True and False, Initial and Current Environments, Scheme Concepts
@subsection Static Scoping
expressions} can be expressed in terms of procedures, this determines
how all bindings behave.
-Consider the following definitions, made at the top-level @sc{rep} loop
-(in the initial environment):
+Consider the following definitions, made at the top-level @acronym{REP}
+loop (in the initial environment):
@example
@group
@cindex binding, variable
@cindex unassigned binding
@cindex binding, unassigned
+@findex condition-type:unassigned-variable
There are several types of bindings that can occur in an environment.
The most common is the simple variable binding, which associates a value
(any Scheme object) with an identifier (a symbol). A variable binding
@cindex keyword binding
@cindex syntactic keyword binding
@cindex binding, syntactic keyword
+@findex condition-type:macro-binding
In addition to variable bindings, an environment can also have
@dfn{keyword bindings}. A keyword binding associates a syntactic
keyword (usually a macro transformer) with an identifier. Keyword
@findex define
The @code{user-initial-environment} is where the top-level
-read-eval-print (@sc{rep}) loop evaluates expressions and stores
-definitions. It is a child of the @code{system-global-environment},
-which is where all of the Scheme system definitions are stored. All of
-the bindings in @code{system-global-environment} are available when the
+read-eval-print (@acronym{REP}) loop evaluates expressions and binds
+definitions. It is a child of @code{system-global-environment}, which
+is where all of the Scheme system definitions are bound. All of the
+bindings in @code{system-global-environment} are available when the
current environment is @code{user-initial-environment}. However, any
-new bindings that you create in the @sc{rep} loop (with @code{define}
-forms or by loading files containing @code{define} forms) occur in
-@code{user-initial-environment}.
+new bindings that you create in the @acronym{REP} loop (with
+@code{define} forms or by loading files containing @code{define} forms)
+occur in @code{user-initial-environment}.
@defvr variable system-global-environment
The variable @code{system-global-environment} is bound to the
distinguished environment that's the ancestor of most other environments
-(except for those created by @code{make-null-top-level-environment}).
+(except for those created by @code{make-root-top-level-environment}).
It is the parent environment of @code{user-initial-environment}.
Primitives, system procedures, and most syntactic keywords are bound
(and sometimes closed) in this environment.
@defvr variable user-initial-environment
The variable @code{user-initial-environment} is bound to the default
environment in which typed expressions are evaluated by the top-level
-@sc{rep} loop.
+@acronym{REP} loop.
Although all bindings in @code{system-global-environment} are visible to
-the @sc{rep} loop, definitions that are typed at, or loaded by, the
-@sc{rep} loop occur in the @code{user-initial-environment}. This is
-partly a safety measure: if you enter a definition that happens to have
-the same name as a critical system procedure, your definition will be
-visible only to the procedures you define in the
+the @acronym{REP} loop, definitions that are typed at, or loaded by, the
+@acronym{REP} loop occur in the @code{user-initial-environment}. This
+is partly a safety measure: if you enter a definition that happens to
+have the same name as a critical system procedure, your definition will
+be visible only to the procedures you define in the
@code{user-initial-environment}; the MIT Scheme system procedures, which
-are defined in the @code{system-global-environment}, will continue to
-see the original definition.
+are defined in @code{system-global-environment}, will continue to see
+the original definition.
@end defvr
@node REPL Environment, Top-level Environments, Environment Variables, Environments
@deffn procedure nearest-repl/environment
@findex user-initial-environment
-Returns the current @sc{rep} loop environment (i.e.@: the current
-environment of the closest enclosing @sc{rep} loop). When Scheme first
-starts up, this is the same as @code{user-initial-environment}.
+Returns the current @acronym{REP} loop environment (i.e.@: the current
+environment of the closest enclosing @acronym{REP} loop). When Scheme
+first starts up, this is the same as @code{user-initial-environment}.
@end deffn
@deffn procedure ge environment
-Changes the current @sc{rep} loop environment to @var{environment}.
+Changes the current @acronym{REP} loop environment to @var{environment}.
@var{Environment} can be either an environment or a procedure object.
If it's a procedure, the environment in which that procedure was closed
is the new environment.
@cindex interpreter environment
@cindex environment, top-level
@cindex environment, interpreter
-The operations in this section manipulate top-level environments, as
-opposed to environments created by the application of procedures. For
-historical reasons, top-level environments are referred to as
+The operations in this section manipulate @dfn{top-level environments},
+as opposed to environments created by the application of procedures.
+For historical reasons, top-level environments are referred to as
@dfn{interpreter environments}.
@deffn {special form} the-environment
@cindex current environment
@cindex environment, current
-Returns the current environment. This form may only appear at the top
-level of a file. An error is signalled if it appears within a
-procedure.
+Returns the current environment. This form may only be evaluated in a
+top-level environment. An error is signalled if it appears elsewhere.
@end deffn
@deffn procedure top-level-environment? object
@end deffn
@deffn procedure extend-top-level-environment environment [names [values]]
-@deffnx procedure make-null-top-level-environment [names [values]]
+@deffnx procedure make-root-top-level-environment [names [values]]
Returns a newly allocated top-level environment.
@code{extend-top-level-environment} creates an environment that has
-parent @var{environment}, while @code{make-null-top-level-environment}
+parent @var{environment}, while @code{make-root-top-level-environment}
creates an environment that has no parent.
The optional arguments @var{names} and @var{values} are used to specify
@cindex standard ports
The next five procedures return the runtime system's @dfn{standard
ports}. All of the standard ports are dynamically bound by the
-@sc{rep} loop; this means that when a new @sc{rep} loop is started,
-for example by an error, each of these ports is dynamically bound to
-the @acronym{I/O} port of the @sc{rep} loop. When the @sc{rep} loop
-exits, the ports revert to their original values.
+@acronym{REP} loop; this means that when a new @acronym{REP} loop is
+started, for example by an error, each of these ports is dynamically
+bound to the @acronym{I/O} port of the @acronym{REP} loop. When the
+@acronym{REP} loop exits, the ports revert to their original values.
@deffn procedure current-input-port
@findex console-input-port
@deffn procedure prompt-for-command-expression prompt [port]
Prompts the user for an expression that is to be executed as a command.
-This is the procedure called by the @sc{rep} loop to read the user's
-expressions.
+This is the procedure called by the @acronym{REP} loop to read the
+user's expressions.
If @var{prompt} is a string, it is used verbatim as the prompt string.
Otherwise, it must be a pair whose car is @code{standard} and whose cdr
is a string; in this case the prompt string is formed by prepending to
-the string the current @sc{rep} loop ``level number'' and a space.
+the string the current @acronym{REP} loop ``level number'' and a space.
Also, a space is appended to the string, unless it already ends in a
space or is an empty string.
If @var{prompt} is a string, it is used verbatim as the prompt string.
Otherwise, it must be a pair whose car is @code{standard} and whose cdr
is a string; in this case the prompt string is formed by prepending to
-the string the current @sc{rep} loop ``level number'' and a space.
+the string the current @acronym{REP} loop ``level number'' and a space.
Also, a space is appended to the string, unless it already ends in a
space or is an empty string.
Prompts the user for an evaluated expression. Calls
@code{prompt-for-expression} to read an expression, then evaluates the
expression using @var{environment}; if @var{environment} is not given,
-the @sc{rep} loop environment is used.
+the @acronym{REP} loop environment is used.
@end deffn
@deffn procedure prompt-for-confirmation prompt [port]
@cindex directory, current working (defn)
@cindex current working directory (defn)
@cindex working directory (see current working directory)
-When MIT Scheme is started, the @dfn{current working
-directory} (or simply, @dfn{working directory}) is initialized in an
-operating-system dependent manner; usually, it is the directory in which
-Scheme was invoked. The working directory can be determined from within
-Scheme by calling the @code{pwd} procedure, and changed by calling the
-@code{cd} procedure. Each @sc{rep} loop has its own working directory,
-and inferior @sc{rep} loops initialize their working directory from the
+When MIT Scheme is started, the @dfn{current working directory} (or
+simply, @dfn{working directory}) is initialized in an operating-system
+dependent manner; usually, it is the directory in which Scheme was
+invoked. The working directory can be determined from within Scheme by
+calling the @code{pwd} procedure, and changed by calling the @code{cd}
+procedure. Each @acronym{REP} loop has its own working directory, and
+inferior @acronym{REP} loops initialize their working directory from the
value in effect in their superior at the time they are created.
@deffn procedure working-directory-pathname
of@* @code{*default-pathname-defaults*} by merging the new working
directory into it.
-When this procedure is executed in the top-level @sc{rep} loop, it
+When this procedure is executed in the top-level @acronym{REP} loop, it
changes the working directory of the running Scheme executable.
@example
projects / mit-scheme.git / commitdiff