CURSOR/SEEKLAST
Sets the cursor at the key value pair with the last key that has a given prefix.
Input stack: cursor prefix
Output stack: b
If there are key/value pairs in the database that have their key
prefixed with prefix, then 1 will be pushed onto the stack and the cursor will be
moved to that pair. Otherwise, 0 will be pushed. Due to non-atomicity of the algorithm,
the position of the cursor is undefined in this case and it is highly recommended to reposition it.
PumpkinDB> ["key" HLC CONCAT 1 ASSOC
"key" HLC CONCAT 2 ASSOC
"key" HLC CONCAT 3 ASSOC COMMIT] WRITE
[CURSOR DUP "key" CURSOR/SEEKLAST DROP CURSOR/VAL] READ
3
Allocation
Allocates for values to be put onto the stack
Errors
NoTransaction error if there's no current write transaction
InvalidValue error if the cursor identifier is incorrect or expired
Tests
lastkey : ["a" HLC CONCAT 0 ASSOC
"key" HLC CONCAT 1 ASSOC
"key" HLC CONCAT 2 ASSOC
"key" HLC CONCAT 3 ASSOC COMMIT] WRITE
[CURSOR DUP "key" CURSOR/SEEKLAST DROP CURSOR/VAL] READ
3 EQUAL?.
not_lastkey : ["key" HLC CONCAT 1 ASSOC
"key" HLC CONCAT 2 ASSOC
"key" HLC CONCAT 3 ASSOC
"zzzz" HLC CONCAT 4 ASSOC COMMIT] WRITE
[CURSOR DUP "key" CURSOR/SEEKLAST DROP CURSOR/VAL] READ
3 EQUAL?.
nextkey_short : ["key" HLC CONCAT 1 ASSOC
"key" HLC CONCAT 2 ASSOC
"key" HLC CONCAT 3 ASSOC
"z" 4 ASSOC COMMIT] WRITE
[CURSOR DUP "key" CURSOR/SEEKLAST DROP CURSOR/VAL] READ
3 EQUAL?.
no_key : ["zzzz" HLC CONCAT 4 ASSOC COMMIT] WRITE
[CURSOR DUP "key" CURSOR/SEEKLAST NOT] READ.
emptydb : [CURSOR DUP "key" CURSOR/SEEKLAST NOT] READ.
requires_txn : ["1" "1" CURSOR/SEEKLAST] TRY UNWRAP 0x08 EQUAL?.
empty_stack : [CURSOR/SEEKLAST] TRY UNWRAP 0x04 EQUAL?.
empty_stack_1 : ["a" CURSOR/SEEKLAST] TRY UNWRAP 0x04 EQUAL?.
invalid_cursor : [["1" "A" CURSOR/SEEKLAST] READ] TRY UNWRAP 0x03 EQUAL?.