4.2.2 Format Specification (Format version 3.1)

Please consult a Common LISP format reference manual for a detailed description of the format string syntax. For a demonstration of the implemented directives see formatst.scm.

This implementation supports directive parameters and modifiers (: and @ characters). Multiple parameters must be separated by a comma (,). Parameters can be numerical parameters (positive or negative), character parameters (prefixed by a quote character ('), variable parameters (v), number of rest arguments parameter (#), empty and default parameters. Directive characters are case independent. The general form of a directive is:

directive ::= ~{directive-parameter,}[:][@]directive-character

directive-parameter ::= [ [-|+]{0-9}+ | 'character | v | # ]

4.2.2.1 Implemented CL Format Control Directives

Documentation syntax: Uppercase characters represent the corresponding control directive characters. Lowercase characters represent control directive parameter descriptions.

~A

Any (print as display does).

~@A

left pad.

~mincol,colinc,minpad,padcharA

full padding.

~S

S-expression (print as write does).

~@S

left pad.

~mincol,colinc,minpad,padcharS

full padding.

~D

Decimal.

~@D

print number sign always.

~:D

print comma separated.

~mincol,padchar,commacharD

padding.

~X

Hexadecimal.

~@X

print number sign always.

~:X

print comma separated.

~mincol,padchar,commacharX

padding.

~O

Octal.

~@O

print number sign always.

~:O

print comma separated.

~mincol,padchar,commacharO

padding.

~B

Binary.

~@B

print number sign always.

~:B

print comma separated.

~mincol,padchar,commacharB

padding.

~nR

Radix n.

~n,mincol,padchar,commacharR

padding.

~@R

print a number as a Roman numeral.

~:@R

print a number as an “old fashioned” Roman numeral.

~:R

print a number as an ordinal English number.

~R

print a number as a cardinal English number.

~P

Plural.

~@P

prints y and ies.

~:P

as ~P but jumps 1 argument backward.

~:@P

as ~@P but jumps 1 argument backward.

~C

Character.

~@C

prints a character as the reader can understand it (i.e. #\ prefixing).

~:C

prints a character as emacs does (eg. ^C for ASCII 03).

~F

Fixed-format floating-point (prints a flonum like mmm.nnn).

~width,digits,scale,overflowchar,padcharF

~@F

If the number is positive a plus sign is printed.

~E

Exponential floating-point (prints a flonum like mmm.nnnEee).

~width,digits,exponentdigits,scale,overflowchar,padchar,exponentcharE

~@E

If the number is positive a plus sign is printed.

~G

General floating-point (prints a flonum either fixed or exponential).

~width,digits,exponentdigits,scale,overflowchar,padchar,exponentcharG

~@G

If the number is positive a plus sign is printed.

~$

Dollars floating-point (prints a flonum in fixed with signs separated).

~digits,scale,width,padchar$

~@$

If the number is positive a plus sign is printed.

~:@$

A sign is always printed and appears before the padding.

~:$

The sign appears before the padding.

~%

Newline.

~n%

print n newlines.

~&

print newline if not at the beginning of the output line.

~n&

prints ~& and then n-1 newlines.

~|

Page Separator.

~n|

print n page separators.

~~

Tilde.

~n~

print n tildes.

~<newline>

Continuation Line.

~:<newline>

newline is ignored, white space left.

~@<newline>

newline is left, white space ignored.

~T

Tabulation.

~@T

relative tabulation.

~colnum,colincT

full tabulation.

~?

Indirection (expects indirect arguments as a list).

~@?

extracts indirect arguments from format arguments.

~(str~)

Case conversion (converts by string-downcase).

~:(str~)

converts by string-capitalize.

~@(str~)

converts by string-capitalize-first.

~:@(str~)

converts by string-upcase.

~*

Argument Jumping (jumps 1 argument forward).

~n*

jumps n arguments forward.

~:*

jumps 1 argument backward.

~n:*

jumps n arguments backward.

~@*

jumps to the 0th argument.

~n@*

jumps to the nth argument (beginning from 0)

~[str0~;str1~;...~;strn~]

Conditional Expression (numerical clause conditional).

~n[

take argument from n.

~@[

true test conditional.

~:[

if-else-then conditional.

~;

clause separator.

~:;

default clause follows.

~{str~}

Iteration (args come from the next argument (a list)). Iteration bounding is controlled by configuration variables format:iteration-bounded and format:max-iterations. With both variables default, a maximum of 100 iterations will be performed.

~n{

at most n iterations.

~:{

args from next arg (a list of lists).

~@{

args from the rest of arguments.

~:@{

args from the rest args (lists).

~^

Up and out.

~n^

aborts if n = 0

~n,m^

aborts if n = m

~n,m,k^

aborts if n <= m <= k

4.2.2.2 Not Implemented CL Format Control Directives

~:A

print #f as an empty list (see below).

~:S

print #f as an empty list (see below).

~<~>

Justification.

~:^

(sorry I don't understand its semantics completely)

4.2.2.3 Extended, Replaced and Additional Control Directives

~mincol,padchar,commachar,commawidthD

~mincol,padchar,commachar,commawidthX

~mincol,padchar,commachar,commawidthO

~mincol,padchar,commachar,commawidthB

~n,mincol,padchar,commachar,commawidthR

commawidth is the number of characters between two comma characters.

~I

print a R4RS complex number as ~F~@Fi with passed parameters for ~F.

~Y

Pretty print formatting of an argument for scheme code lists.

~K

Same as ~?.

~!

Flushes the output if format destination is a port.

~_

Print a #\space character

~n_

print n #\space characters.

~/

Print a #\tab character

~n/

print n #\tab characters.

~nC

Takes n as an integer representation for a character. No arguments are consumed. n is converted to a character by integer->char. n must be a positive decimal number.

~:S

Print out readproof. Prints out internal objects represented as #<...> as strings "#<...>" so that the format output can always be processed by read.

~:A

Print out readproof. Prints out internal objects represented as #<...> as strings "#<...>" so that the format output can always be processed by read.

~Q

Prints information and a copyright notice on the format implementation.

~:Q

prints format version.

~F, ~E, ~G, ~$

may also print number strings, i.e. passing a number as a string and format it accordingly.

4.2.2.4 Configuration Variables

Format has some configuration variables at the beginning of format.scm to suit the systems and users needs. There should be no modification necessary for the configuration that comes with SLIB. If modification is desired the variable should be set after the format code is loaded. Format detects automatically if the running scheme system implements floating point numbers and complex numbers.

format:symbol-case-conv

Symbols are converted by symbol->string so the case type of the printed symbols is implementation dependent. format:symbol-case-conv is a one arg closure which is either #f (no conversion), string-upcase, string-downcase or string-capitalize. (default #f)

format:iobj-case-conv

As format:symbol-case-conv but applies for the representation of implementation internal objects. (default #f)

format:expch

The character prefixing the exponent value in ~E printing. (default #\E)

format:iteration-bounded

When #t, a ~{...~} control will iterate no more than the number of times specified by format:max-iterations regardless of the number of iterations implied by modifiers and arguments. When #f, a ~{...~} control will iterate the number of times implied by modifiers and arguments, unless termination is forced by language or system limitations. (default #t)

format:max-iterations

The maximum number of iterations performed by a ~{...~} control. Has effect only when format:iteration-bounded is #t. (default 100)

4.2.2.5 Compatibility With Other Format Implementations

SLIB format 2.x:

See format.doc.

SLIB format 1.4:

Downward compatible except for padding support and ~A, ~S, ~P, ~X uppercase printing. SLIB format 1.4 uses C-style printf padding support which is completely replaced by the CL format padding style.

MIT C-Scheme 7.1:

Downward compatible except for ~, which is not documented (ignores all characters inside the format string up to a newline character). (7.1 implements ~a, ~s, ~newline, ~~, ~%, numerical and variable parameters and :/@ modifiers in the CL sense).

Elk 1.5/2.0:

Downward compatible except for ~A and ~S which print in uppercase. (Elk implements ~a, ~s, ~~, and ~% (no directive parameters or modifiers)).

Scheme->C 01nov91:

Downward compatible except for an optional destination parameter: S2C accepts a format call without a destination which returns a formatted string. This is equivalent to a #f destination in S2C. (S2C implements ~a, ~s, ~c, ~%, and ~~ (no directive parameters or modifiers)).

This implementation of format is solely useful in the SLIB context because it requires other components provided by SLIB.