Format is an atom, list of ASCII values, or a Prolog string.
Arguments provides the arguments required by the format
specification. If only one argument is required and this is not a list
of ASCII values the argument need not be put in a list. Otherwise the
arguments are put in a list.
Special sequences start with the tilde (~), followed by an optional
numeric argument, followed by a character describing the action to be
undertaken. A numeric argument is either a sequence of digits,
representing a positive decimal number, a sequence `<character>,
representing the ASCII value of the character (only useful for
~t) or a asterisk (*), in when the numeric argument is taken
from the next argument of the argument list, which should be a positive
integer. Actions are:
-1ex
-
Output the tilde itself.
- a
-
Output the next argument, which should be an atom. This option is
equivalent to w. Compatibility reasons only.
- c
-
Output the next argument as an ASCII value. This argument should be an
integer in the range [0, ..., 255] (including 0 and 255).
- d
-
Output next argument as a decimal number. It should be an integer. If
a numeric argument is specified a dot is inserted argument
positions from the right (useful for doing fixed point arithmetic with
integers, such as handling amounts of money).
- D
-
Same as d, but makes large values easier to read by inserting a
comma every three digits left to the dot or right.
- e
-
Output next argument as a floating point number in exponentional
notation. The numeric argument specifies the precission. Default is 6
digits. Exact representation depends on the C library function
printf(). This function is invoked with the format
%.<percission>e.
- E
-
Equivalent to e, but outputs a capital E to indicate the exponent.
- f
-
Floating point in non-exponentional notation. See C library function
printf().
- g
-
Floating point in e or f notation, whichever is shorter.
- G
-
Floating point in E or f notation, whichever is shorter.
- i
-
Ignore next argument of the argument list. Produces no output.
- k
-
Give the next argument to displayq/1 (canonical write).
- n
-
Output a newline character.
- N
-
Only output a newline if the last character output on this stream was
not a newline. Not properly implemented yet.
- p
-
Give the next argument to print/1.
- q
-
Give the next argument to writeq/1.
- r
-
Print integer in radix the numeric argument notation. Thus
~16r
prints its argument hexadecimal. The argument should be in the range
[2, ... 36]. Lower case letters are used for digits above 9.
- R
-
Same as r, but uses upper case letters for digits above 9.
- s
-
Output a string of ASCII characters from the next argument.
- t
-
All remaining space between 2 tabstops is distributed equaly over
~t statements between the tabstops. This space is padded with
spaces by default. If an argument is supplied this is taken to be the
ASCII value of the character used for padding. This can be used to do
left or right alignment, centering, distributing, etc. See also
~| and ~+ to set tab stops. A tabstop is assumed at the
start of each line.
-
-
Set a tabstop on the current position. If an argument is supplied set a
tabstop on the position of that argument. This will cause all
~t's
to be distributed between the previous and this tabstop.
- +
-
Set a tabstop relative to the current position. Further the same as
~|.
- w
-
Give the next argument to write/1.
Example:
simple_statistics :-
<obtain statistics> % left to the user
format('~tStatistics~t~72|~n~n'),
format('Runtime: ~`.t ~2f~34| Inferences: ~`.t ~D~72|~n',
[RunT, Inf]),
....
Will output
Statistics
Runtime: .................. 3.45 Inferences: .......... 60,345
