20.2.0 2The top level loop is not completely specified; thus the user interface is implementation-defined. 20.2.0 3 Moon deleted the following sentence The top level loop traps all attempts to \term{throw} and recovers from them.The top level loop prints all values resulting from the evaluation of a form. 20.2.0 4The next figure lists variables that are maintained by the Lisp read-eval-print loop.
*debugger-hook* | documentation | step |
apropos | dribble | time |
apropos-list | ed | trace |
break | inspect | untrace |
describe | invoke-debugger |
Figure 25–2. Defined names relating to debugging
The next figure shows defined names relating to environment inquiry.
*features* | machine-instance | short-site-name |
lisp-implementation-type | machine-type | software-type |
lisp-implementation-version | machine-version | software-version |
long-site-name | room |
Figure 25–3. Defined names relating to environment inquiry.
Removed identity! -kmp 3-Jan-91
25.4.1 1Time is represented in four different ways in Common Lisp: decoded time, universal time, internal time, and seconds. Decoded time and universal time are used primarily to represent calendar time, and are precise only to one second. Internal time is used primarily to represent measurements of computer time (such as run time) and is precise to some implementation-dependent fraction of a second called an internal time unit, as specified by internal-time-units-per-second. Actually, relative universal times aren't actually used for anything.
But it didn't seem worth removing the mention, since it's a legit concept. -kmp 9-Sep-91
Moon wanted this shifted to say that Universal time is only absolute.
\term{Decoded time} is used only for \term{absolute} \term{time} indications.
\term{Universal time} and \term{internal time} formats are used for both \term{absolute}
and \term{relative} \term{times}.An internal time can be used for either absolute and relative time measurements. Both a universal time and a decoded time can be used only for absolute time measurements. This may be gratuitous, but I just want to be clear.In the case of one function, sleep, time intervals are represented as a non-negative real number of seconds.
The next figure shows defined names relating to time.
decode-universal-time | get-internal-run-time |
encode-universal-time | get-universal-time |
get-decoded-time | internal-time-units-per-second |
get-internal-real-time | sleep |
Figure 25–4. Defined names involving Time.
25.4.1 2A decoded time is an ordered series of nine values that, taken together, represent a point in calendar time (ignoring leap seconds):
25.4.1 3
An integer between 0 and 59, inclusive.
25.4.1 4
An integer between 0 and 59, inclusive.
25.4.1 5
An integer between 0 and 23, inclusive.
25.4.1 6
An integer between 1 and 31, inclusive (the upper limit actually depends on the month and year, of course).
25.4.1 7
An integer between 1 and 12, inclusive; 1 means January, 2 means February, and so on; 12 means December.
25.4.1 8
An integer indicating the year A.D. However, if this integer is between 0 and 99, the “obvious” year is used; more precisely, that year is assumed that is equal to the integer modulo 100 and within fifty years of the current year (inclusive backwards and exclusive forwards). Thus, in the year 1978, year 28 is 1928 but year 27 is 2027. (Functions that return time in this format always return a full year number.)
25.4.1 10
An integer between 0 and 6, inclusive; 0 means Monday, 1 means Tuesday, and so on; 6 means Sunday.
25.4.1 11
A generalized boolean that, if true, indicates that daylight saving time is in effect.
25.4.1 12
A time zone.
The next figure shows defined names relating to decoded time.
decode-universal-time | get-decoded-time |
Figure 25–5. Defined names involving time in Decoded Time.
25.4.1 13 \newtermidx{Universal time}{universal time} represents time as a single non-negative \term{integer}. For \term{relative} time purposes, this is a number of seconds. For absolute time, this is the number of seconds since midnight, January 1, 1900 GMT (ignoring \term{leap seconds}).Universal time is an absolute time represented as a single non-negative integer—the number of seconds since midnight, January 1, 1900 GMT (ignoring leap seconds). Thus the time 1 is 00:00:01 (that is, 12:00:01 a.m.) on January 1, 1900 GMT. Similarly, the time 2398291201 corresponds to time 00:00:01 on January 1, 1976 GMT. Recall that the year 1900 was not a leap year; for the purposes of Common Lisp, a year is a leap year if and only if its number is divisible by 4, except that years divisible by 100 are not leap years, except that years divisible by 400 are leap years. Therefore the year 2000 will be a leap year. Because universal time must be a non-negative integer, times before the base time of midnight, January 1, 1900 GMT cannot be processed by Common Lisp.
decode-universal-time | get-universal-time |
encode-universal-time |
Figure 25–6. Defined names involving time in Universal Time.
25.4.1 14Internal time represents time as a single integer, in terms of an implementation-dependent unit called an internal time unit. Relative time is measured as a number of these units. Absolute time is relative to an arbitrary time base.
The next figure shows defined names related to internal time.
get-internal-real-time | internal-time-units-per-second |
get-internal-run-time |
Figure 25–7. Defined names involving time in Internal Time.
sleep, takes its argument as a non-negative real number of seconds. Informally, it may be useful to think of this as a relative universal time, but it differs in one important way: universal times are always non-negative integers, whereas the argument to sleep can be any kind of non-negative real, in order to allow for the possibility of fractional seconds.
sleep |
Figure 25–8. Defined names involving time in Seconds.
decode-universal-time Functionencode-universal-time Functionget-universal-time, get-decoded-time Functionsleep Functionapropos, apropos-list Functiondescribe Functiondescribe-object Standard Generic Functiontrace, untrace Macrostep Macrotime Macrointernal-time-units-per-second Constant Variableget-internal-real-time Functionget-internal-run-time Functiondisassemble Functiondocumentation, (setf documentation) Standard Generic Functionroom Functioned Functioninspect Functiondribble Function- Variable+, ++, +++ Variable*, **, *** Variable/, //, /// Variablelisp-implementation-type, lisp-implementation-version Functionshort-site-name, long-site-name Functionmachine-instance Functionmachine-type Functionmachine-version Functionsoftware-type, software-version Functionuser-homedir-pathname Function