[cl-json-devel] Encoding DOUBLE-FLOAT

[Robert Goldman]

On 6/22/11 Jun 22 -11:59 AM, Daniel Brunner wrote:
> (json:encode-json-to-string 0.0570714084012434D0)

I have replicated this error....

The bug is here:

(defun write-json-number (nr stream)
  "Write the JSON representation of the number NR to STREAM."
  (typecase nr
    (integer (format stream "~d" nr))
    (real (format stream "~f" nr))
    (t (unencodable-value-error nr 'write-json-number))))

As can be seen by

CL-USER> (format t "~f" 0.0570714084012434D0)
0.0570714084012434D0
NIL

This suggests that we must avoid using FORMAT in translating floats to
strings for JSON, or that there's a recipe for getting FORMAT to shun
the D that I don't know about....

Not incredibly well thought out or tested patch:

(defun write-json-number (nr stream)
  "Write the JSON representation of the number NR to STREAM."
  (typecase nr
    (integer (format stream "~d" nr))
    (real (let* ((raw (format nil "~f" nr))
                 (dpos (position #\d raw :test 'char-equal)))
           (princ (subseq raw 0 dpos) stream)))
    (t (unencodable-value-error nr 'write-json-number))))

This checks for D in the output.  I /believe/ that this is the only such
character that can creep in, but I am far from being an expert on this.

Best,
r