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Article contents:== Outdated egg! This is an egg for CHICKEN 4, the unsupported old release. You're almost certainly looking for [[/eggref/5/describe|the CHICKEN 5 version of this egg]], if it exists. If it does not exist, there may be equivalent functionality provided by another egg; have a look at the [[https://wiki.call-cc.org/chicken-projects/egg-index-5.html|egg index]]. Otherwise, please consider porting this egg to the current version of CHICKEN. == describe Display textual descriptions of built-in objects and user-created records. == Overview The native {{csi}} describe mechanism ({{,d}} and friends) is only available at the REPL. This egg makes it available to programs, and also extends it a bit. To describe [[/egg/coops|coops]] objects, see the [[/egg/describe-coops|describe-coops]] extension. == REPL usage This egg adds the following convenient REPL shortcuts to {{describe}} and {{dump}}: ,d EXP (describe) Describe result of evaluated EXP ,du EXP (describe) Hexdump contents of bytevector EXP ,dur EXP LEN (describe) Hexdump first LEN bytes of bytevector EXP ,dus EXP OFF LEN (describe) Hexdump LEN bytes of bytevector EXP at offset OFF == API <procedure>(describe obj #!optional out)</procedure> Prints a textual description of {{OBJ}} to output port {{OUT}}, which defaults to {{(current-output-port)}}. <procedure>(dump obj #!optional offset length out)</procedure> Hexdump the contents of {{OBJ}} to output port {{OUT}}, starting at {{OFFSET}} and continuing for {{LENGTH}} bytes. Offset defaults to 0, length to {{#f}} (meaning, until the end) and output to {{(current-output-port)}}. If dumping a {{pointer}} object, length defaults to 32 bytes, as the underlying length is unknown to us. <parameter>(describe-sequence-limit n)</parameter> Limit the number of elements displayed to {{N}} when describing the contents of a sequence -- e.g. a list, vector, bytevector, hash table or string. Defaults to 40. #;6> (parameterize ((describe-sequence-limit 5)) (describe (iota 100))) list of length 100 0: 0 1: 1 2: 2 3: 3 4: 4 (95 elements not displayed) <procedure>(set-describer! TAG PROC)</procedure> Sets a custom description handler that invokes {{PROC}} when the {{,d}} or {{describe}} command is invoked with a record-type object that has the type {{TAG}} (a symbol). {{PROC}} is called with two arguments: the object to be described and an output-port. It should write a possibly useful textual description of the object to the passed output-port. For example: #;1> (define-record-type point (make-point x y) point? (x point-x) (y point-y)) #;2> (set-describer! 'point (lambda (pt o) (with-output-to-port o (lambda () (print "a point with x=" (point-x pt) " and y=" (point-y pt)))))) #;3> ,d (make-point 1 2) a point with x=1 and y=2 == Low-level API <procedure>(hexdump bv start end ref out)</procedure> Hexdump the contents of bytevector-like object {{BV}} from offset {{START}} to offset {{END}}, to output port {{OUT}}. {{REF}} is a procedure of two arguments, {{(obj i)}}, which should return the byte value of {{OBJ}} at offset {{I}}. An example of {{REF}} for a u8vector might be {{u8vector-ref}}. For string it might be {{(λ (obj i) (char->integer (string-ref obj i)))}}, or even {{##sys#byte}} if you want to live dangerously. {{dump}} provides a high-level interface to this procedure. == Version history ; 0.1 : Initial release == Author [[/users/jim-ursetto|Jim Ursetto]], [[http://ursetto.com|Ursetto Consulting, Inc.]] Much of the code was taken from Chicken's {{csi.scm}}. == License [[https://bitbucket.org/ursetto/describe/raw/tip/LICENSE.txt|3-clause BSD]]. Description of your changes:

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