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This is a proposal for environment inquiry, providing human-readable information at run time about the hardware and software configuration on which a Scheme program is being executed. They are mostly based on Common Lisp, with additions from the Posix
uname() system call.
None for this draft.
The feature symbols of the R7RS-small
cond-expand syntax provide the ability to conditionally compile code based on particular properties of an implementation that it sees fit to publish. The
features procedure, which returns the list of feature symbols of the implementation, provides run-time access to the same set of properties. Assuming that Rhinoceros Scheme provides the feature symbol
rhinoceros but not
diplodocus and Diplodocus Scheme does the opposite, programs can portably ask "Is this Rhinoceros Scheme or Diplodocus Scheme?" and behave differently at run time based on the answer. Similarly, a program can ask "Does this implementation have exact complex numbers?" by checking for the presence of the
exact-complex feature symbol in the result of calling
However, a program using just the
features procedure cannot report to its user "I am executing on X Scheme" for every value of X, because it does not know which symbol in the feature list represents the implementation name, nor does it have a comprehensive list of implementation names. Similarly, there are other properties that the feature list may allow testing for but not reporting on, such as the underlying OS and the CPU architecture. For the sake of logging and debugging, it is necessary or at least extremely useful to provide a standard way for Scheme applications, as well as Scheme users at the REPL, to report these things. In the Common Lisp world, bugs are often reported in a REPL transcript beginning with a call to
The following procedures take no arguments and return either a string, or
#f if the implementation cannot provide an appropriate and relevant result. It is an error to mutate the returned string. The procedures in this proposal are in the
(srfi 112) library (or
(srfi :112) on R6RS).
Because users are expected to use the values of these procedures for reporting rather than testing, no attempt is made to standardize the string values they return.
Procedures are provided rather than strings against the possibility that a Scheme process might migrate from machine to machine. This need not happen only in a distributed environment; consider, for example, dumping a core image file containing a compiler and then shipping it to another site.
Posix and Common Lisp equivalents or near-equivalents are provided. On Windows, some of this information is available using the
Returns the name of the Scheme implementation. This procedure corresponds roughly to Common Lisp's
Returns the version of the Scheme implementation. This procedure corresponds roughly to Common Lisp's
Returns the CPU architecture, real or virtual, on which this implementation is executing. This procedure corresponds roughly to Common Lisp's
machine-type function. On Posix systems, the result may be derived from the
machine field of the
Returns a name for the particular machine on which the implementation is running. Possible values are the DNS or WINS host name, the DNS full name, an IP address in string form associated with the system, or a MAC address in string form associated with the system. This procedure corresponds roughly to Common Lisp's
machine-instance function. On Posix systems, the result may be derived from the
nodename field of the
Returns a name for the operating system, platform, or equivalent on which the implementation is running. This procedure corresponds roughly to Common Lisp's
software-type function. On Posix systems, the result may be derived from the
sysname field of the
Returns the version of the operating system, platform, or equivalent on which the implementation is running. This procedure corresponds roughly to Common Lisp's
software-version function. On Posix systems, the result may be derived from the
version fields of the
Note: Analogues to the Common Lisp
long-site-name are not provided. They are inconsistently implemented and of doubtful utility.
The implementation of this SRFI is inherently system-dependent. The version shown below is for an imaginary Scheme implementation, and is in R5RS style. Trivial wrappers will convert it to an R6RS or R7RS library.
Some of the information can be derived from the
uname() system call, which is provided by the Posix standard. (Some of the same information is available on Win32 using
GetComputerNameA.) The exact Scheme interface to
uname is highly system-dependent. In Chicken, the
system-information procedure returns a list of five strings representing the five components of the Posix
utsname structure. In Gauche, the same procedure is called
sys-uname. In Guile and Sizzle, it is called
uname, and returns a vector rather than a list; Sizzle places it in the module
(core posix). In Scheme48, there are five separate procedures in the
posix structure named
machine-name. In scsh, the uname procedure returns a record whose fields have the same names as the Scheme48 procedures; their accessors are named uname:os-name, etc. The version below uses the Guile convention.
(define (implementation-name) "Fantastic Scheme") (define (implementation-version) "1.0") (define (cpu-architecture) (vector-ref (uname) 4)) ; Posix machine field (define (machine-name) (vector-ref (uname) 1)) ; Posix nodename field (define (os-name) (vector-ref (uname) 0)) ; Posix sysname field (define (os-version) (string-append (vector-ref (uname) 2) ; Posix version field " " (vector-ref (uname) 3))) ; Posix release field
Copyright (C) John Cowan 2013. All Rights Reserved.
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