A library of procedures for formatting Scheme objects to text in various ways, and for easily concatenating, composing and extending these formatters.
There are several approaches to text formatting. Building strings
display is not acceptable, since it doesn't scale to
very large output. The simplest realistic idea, and what people
resort to in typical portable Scheme, is to interleave
write and manual loops, but this is
both extremely verbose and doesn't compose well. A simple concept
such as padding space can't be achieved directly without somehow
capturing intermediate output.
The traditional approach is to use templates - typically strings,
though in theory any object could be used and indeed Emacs'
mode-line format templates allow arbitrary sexps. Templates can
use either escape sequences (as in C's
format) or pattern matching (as in Visual Basic's
form, and SQL date formats). The primary disadvantage of
templates is the relative difficulty (usually impossibility) of
extending them, their opaqueness, and the unreadability that
arises with complex formats. Templates are not without their
advantages, but they are already addressed by other libraries such
This library takes a combinator approach. Formats are nested chains of closures, which are called to produce their output as needed. The primary goal of this library is to have, first and foremost, a maximally expressive and extensible formatting library. The next most important goal is scalability - to be able to handle arbitrarily large output and not build intermediate results except where necessary. The third goal is brevity and ease of use.
The primary interface. Analogous to CL's
format, the first
argument is either an output port or a boolean, with
#f indicating a
string port. The remaining arguments are formatters, combined as with
each, run with output to the given destination. If
#f then the accumulated output is returned, otherwise
the result is unspecified.
Output a single newline.
"Fresh line" - output a newline iff we're not at the start of a fresh line.
Move to a given tab-stop (using spaces, not tabs).
Move to an explicit column.
Show each of
ls, uppercasing all generated text.
Show each of
ls, lowercasing all generated text.
Pad the result of
(each-in-list ls) to at least
width characters, equally applied to the left and right,
with any extra odd padding applied to the right. Uses the value
pad-char for padding, defaulting to
padded/both but only applies padding on the right.
An alias for
padded/both but only applies padding on the left.
Trims the result of
(each-in-list ls) to at most
width characters, removed from the right. If any characters
are removed, then the value of
ellipsis (default empty)
is used in its place (trimming additional characters as needed to
be sure the final output doesn't exceed
An alias for
trimmed but removes from the left.
trimmed but removes equally from both the left and the
right, removing extra odd characters from the right, and inserting
ellipsis on both sides.
trimmed, but truncates and terminates immediately if
width characters are generated by
ls may lazily generate an infinite amount of output safely
write-simple on an infinite list). The nature of
this procedure means only truncating on the right is meaningful.
Fits the result of
(each-in-list ls) to exactly
width characters, padding or trimming on the right as
needed.An alias for
fitted but pads/trims from the left.
fitted but pads/trims equally from both the left and
Joins the result of applying
elt-f to each element of the
ls together with
sep, which defaults to the empty
joined but treats the separator as a prefix, inserting
before every element instead of between.
joined but treats the separator as a suffix, inserting
after every element instead of between.
joined but applies
last-f, instead of
elt-f, to the last element of
ls, useful for
e.g. commas separating a list with "and" before the final element.
joined but if
ls is a dotted list applies
dot-f to the dotted tail as a final element.