The change to ~a, ~v, and ~s seems reasonable to me. The renamed
keywords and generalization of ~v and ~s to multiple arguments are good.
The ~r function seems okay except for the way it chooses which notation
(positional or exponential) to use. It should take a rule, not an
answer, and the default rule should not depend on the precision
argument, as it produces peculiar results. Contrast:
(catn pi #:precision 0) = "3"
(~r pi #:precision 0) = "3e+00"
Unfortunately, I think the kind of rules supported by 'catn'
(pos/exp-range) are also wrong. Probably the best solution is to take a
function. I'll change ~r to drop the #:exponential? argument and instead
take a #:notation argument, with contract
(or/c 'positional 'exponential
(-> rational? (or/c 'positional 'exponential)))
and default value of 'positional.
Ryan
On 09/07/2012 10:27 AM, Matthew Flatt wrote:
I've added a `racket/format' library that is a revised version of
Ryan's `unstable/cat'. It's re-exported by `racket', but not by
`racket/base'.
I think Ryan's library is a step in the right direction for string
formatting, and the difficult remaining task is getting the names
right. So, this `racket/format' experiment changes all of the names.
As reflected in the `racket/format' library name, the new function
names are intended to leverage your experience with `format': the `cat'
function is `~a', the `catp' function is `~v', and the `catw' function
is `~s'. The `catn' functions are collapsed to a single `~r'.
Using this library, instead of writing
(format "The result of\n ~s\nis\n ~v"
expr
(eval expr))
you'd write
(~a "The result of\n"
" " (~s expr) "\n"
"is\n"
" " (~v (eval expr)))
or even, when using `#lang at-exp racket',
@~a{The result of
@~s[expr]
is
@~v[(eval expr)]}
Keyword options like `#:width' and `#:align', of course, can be an even
bigger help for formatting.
I concede that names like `~s' are not remotely mnemonic unless you've
already learned the somewhat obscure `format' escapes, but it seems
difficult to find compact names that are meaningful and that don't
cause collisions; we can at least take advantage of the compact names
that we've already learned. Embracing tildes also means that we worry
less about replacing all sorts of APIs, such as `error', that have
`format' built in. And maybe `~a' works relatively well as a shorthand
for `string-append'.
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