hash code for a type string is not the same as hash code for the same string read by the reader ('the member bug') #6

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opened 2026-02-26 09:09:47 +00:00 by simon · 0 comments

simon commented

2026-02-26 09:09:47 +00:00

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member is failing, and it transpires that the hash code for a type string is computed differently from one for an identical string read by the reader:

:: (type member)

"LMDA"
:: (get-hash (type member))

397,936
:: (get-hash "LMDA")

25,865,840
:: (get-hash "LMD")

397,936

(this pattern is repeated for other strings returned by type).

So it appears that the hash for a type string is computed only for the first three characters (why?)

Note that this is not the only bug in member, but it needs fixed anyway.

member is failing, and it transpires that the hash code for a type string is computed differently from one for an identical string read by the reader: ```lisp :: (type member) "LMDA" :: (get-hash (type member)) 397,936 :: (get-hash "LMDA") 25,865,840 :: (get-hash "LMD") 397,936 ``` (this pattern is repeated for other strings returned by `type`). So it appears that the hash for a type string is computed only for the first three characters (why?) Note that this is not the only bug in `member`, but it needs fixed anyway.