Rich mentioned on #clojure that a patch to implement *print-length*
would be welcome.
I've uploaded a patch that implements Common Lisp's *print-length* and
*print-level* for Clojure:
http://clojure.googlegroups.com/web/print-length-level.patch
The CL docs are at:
http://www.lispworks.com/documentation/HyperSpec/Body/v_pr_lev.htm
*print-length* can be especially useful in Clojure's repl to avoid
accidentally printing an infinite seq and having to abort your session.
I've enclosed an example and docs below.
Notes:
- I changed the print method for vector to use print-sequential. It
didn't seem essential to avoid print-sequential and it allowed me to
implement *print-length* and *print-level* in one place where it's
intended to be effective for all collections.
- I was surprised to find what appears to be an error in the Common
Lisp Hyperspec. The output for length = 5 in the example for *print-
length* gives the desired out as (1 2 3 4 5 6). My reading of the docs
and tests I ran with CLISP and sbcl all indicate the output should be
(1 2 3 4 5 ...). I implemented the latter.
- We have no dotted lists in Clojure so the special case for *print-
length* with a dotted list doesn't apply.
- I added these variables to the group whose bindings are pushed and
popped in Repl.java so that we can use set! to set them in the repl.
--Steve
Clojure
user=> (set! *print-length* 100)
100
user=> (iterate inc 1)
(1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49
50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72
73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
96 97 98 99 100 ...)
user=> (doc *print-length*)
-------------------------
clojure/*print-length*
nil
*print-length* controls how many items of each collection the
printer will print. If it is bound to logical false, there is no
limit. Otherwise, it must be bound to an integer indicating the
maximum
number of items of each collection to print. If a collection contains
more items, the printer will print items up to the limit followed by
'...' to represent the remaining items. The root binding is nil
indicating no limit.
nil
user=> (doc *print-level*)
-------------------------
clojure/*print-level*
nil
*print-level* controls how many levels deep the printer will
print nested objects. If it is bound to logical false, there is no
limit. Otherwise, it must be bound to an integer indicating the
maximum
level to print. Each argument to print is at level 0; if an
argument is a
collection, its items are at level 1; and so on. If an object is a
collection and is at a level greater than or equal to the value
bound to
*print-level*, the printer prints '#' to represent it. The root
binding
is nil indicating no limit.
nil
user=>
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