# U

`*Uni`
  A global variable holding an `idx` tree, with all unique data that were collected with the comma (`,`) read-macro. Typically used for localization. Setting `*Uni` to `T` disables this mechanism. See also `Read-Macros` and `locale`.

      : (off *Uni)            # Clear
      -> NIL
      : ,"abc"                # Collect a transient symbol
      -> "abc"
      : ,(1 2 3)              # Collect a list
      -> (1 2 3)
      : *Uni
      -> ("abc" NIL (1 2 3))

`+UB`
  Prefix class for `+Aux` to maintain an UB-Tree index instead of the direct values. This allows efficient range access to multi-dimensional data. Only positive numeric keys are supported. See also `ubIter` and Database.

      (class +Pos +Entity)
      (rel x (+UB +Aux +Ref +Number) (y z))
      (rel y (+Number))
      (rel z (+Number))

      : (scan (tree 'x '+Pos))
      (288362200753438306 . {13}) {13}
      (348187139486943716 . {16}) {16}
      (605261596962573238 . {11}) {11}
      (638523558602802506 . {7}) {7}   # UBKEY of (453062 450921 613956)
      (654697989157410399 . {12}) {12}
      ...

      : (show '{7})
      {7} (+Pos)
         x 453062
         y 450921
         z 613956
      -> {7}

      # Discrete queries work the same way as without the +UB prefix
      : (db 'x '+Pos 453062 'y 450921 'z 613956)
      -> {7}
      : (aux 'x '+Pos 453062 450921 613956)
      -> {7}
      : (? (db x +Pos (453062 450921 613956) @Pos))
       @Pos={7}
      -> NIL

      # Range queries work efficiently with 'collect'. Note that though also Pilog
      queries can handle UB-trees, they may do so sub-optimally for certain ranges.
      : (collect 'x '+Pos (200000 200000 200000) (899999 899999 899999))
      -> ({7} {14} {17} {15})

`(u) -> T`
  (Debug mode only) Removes `!` all breakpoints in all subexpressions of the current breakpoint. Typically used when single-stepping a function or method with `debug`. See also `d` and `unbug`.

      ! (u)                         # Unbug subexpression(s) at breakpoint
      -> T

`(ubIter 'tree 'dim 'fun 'lst1 'lst2)`
  Efficiently iterates through a database `+UB` tree, by applying `fun` to all values. `dim` is the number of the key dimensions, `lst1` and `lst2` specify a range of keys. `collect` uses `ubIter` internally for UB-tree queries. See also `iter`.

      : (ubIter (tree 'x '+Pos) 3 show (200000 200000 200000) (899999 899999 899999))
      {7} (+Pos)
         z 613956
         y 450921
         x 453062
      {14} (+Pos)
         z 771372
         y 262217
         x 862358
      {17} (+Pos)
         z 676836
         y 529576
         x 398229
      {15} (+Pos)
         z 889332
         y 691799
         x 265381
      -> NIL

`(udp 'any1 'any2 'any3) -> any`
`(udp 'cnt) -> any`
  Simple unidirectional sending/receiving of UDP packets. In the first form, `any3` is sent to a UDP server listening at host `any1`, port `any2`. In the second form, one item is received from a UDP socket `cnt`, established with `port`. See also `listen` and `connect`.

      # First session
      : (port T 6666)
      -> 3
      : (udp 3)  # Receive a datagram

      # Second session (on the same machine)
      : (udp "localhost" 6666 '(a b c))
      -> (a b c)

      # First session
      -> (a b c)

`(ultimo 'y 'm) -> cnt`
  Returns the `date` of the last day of the month `m` in the year `y`. See also `day` and `week`.

      : (date (ultimo 2007 1))
      -> (2007 1 31)
      : (date (ultimo 2007 2))
      -> (2007 2 28)
      : (date (ultimo 2004 2))
      -> (2004 2 29)
      : (date (ultimo 2000 2))
      -> (2000 2 29)
      : (date (ultimo 1900 2))
      -> (1900 2 28)

`(unbug 'sym) -> T`
`(unbug 'sym 'cls) -> T`
`(unbug '(sym . cls)) -> T`
  (Debug mode only) Removes all `!` breakpoints in the function or method body of sym, as inserted with `debug` or `d`, or directly with `vi`. See also `u`.

      : (pp 'tst)
      (de tst (N)
         (! println (+ 3 N)) )         # 'tst' has a breakpoint '!'
      -> tst
      : (unbug 'tst)                   # Unbug it
      -> T
      : (pp 'tst)                      # Restore
      (de tst (N)
         (println (+ 3 N)) )

`(undef 'sym) -> fun`
`(undef 'sym 'cls) -> fun`
`(undef '(sym . cls)) -> fun`
  Undefines the function or method `sym`. Returns the previous definition. See also `de`, `dm`, `def` and `redef`.

      : (de hello () "Hello world!")
      -> hello
      : hello
      -> (NIL "Hello world!")
      : (undef 'hello)
      -> (NIL "Hello world!")
      : hello
      -> NIL

`(unify 'any) -> lst`
  Unifies `any` with the current Pilog environment at the current level and with a value of `NIL`, and returns the new environment or `NIL` if not successful. See also `prove` and `->`.

      : (? (^ @A (unify '(@B @C))))
       @A=(((NIL . @C) 0 . @C) ((NIL . @B) 0 . @B) T)

`(uniq 'lst) -> lst`
  Returns a unique list, by eliminating all duplicate elements from `lst`. See also Comparing, `sort` and `group`.

      : (uniq (2 4 6 1 2 3 4 5 6 1 3 5))
      -> (2 4 6 1 3 5)

`uniq/2`
  Pilog predicate that succeeds if the second argument is not yet stored in the first argument's index structure. `idx` is used internally storing for the values and checking for uniqueness. See also `member/2`.

      : (let U NIL
         (? (lst @X (a b c b c d)) (uniq U @X)) )
       @X=a
       @X=b
       @X=c
       @X=d
      -> NIL
      : (solve '((^ @B (box)) (lst @X (a b c b c d)) (uniq @B @X)) @X)
      -> (a b c d)

`(unless 'any . prg) -> any`
  Conditional execution: When the condition `any` evaluates to non-`NIL`, `NIL` is returned. Otherwise `prg` is executed and the result returned. See also `when`, `ifn`, `nor`, `nand` and `nond`.

      : (unless (= 3 3) (println 'Strange 'result))
      -> NIL
      : (unless (= 3 4) (println 'Strange 'result))
      Strange result
      -> result

`(until 'any . prg) -> any`
  Conditional loop: While the condition `any` evaluates to `NIL`, `prg` is repeatedly executed. If `prg` is never executed, `NIL` is returned. Otherwise the result of `prg` is returned. See also `while`, `for`, `loop` and `do`.

      : (until (=T (setq N (read)))
         (println 'square (* N N)) )
      4
      square 16
      9
      square 81
      T
      -> 81

`(untrace 'sym) -> sym`
`(untrace 'sym 'cls) -> sym`
`(untrace '(sym . cls)) -> sym`
  (Debug mode only) Removes the `$` trace function call at the beginning of the function or method body of `sym`, so that no more trace information will be printed before and after execution. Built-in functions (SUBRs) are automatically converted to their original form (see `subr`). See also `trace` and `traceAll`.

      : (trace '+)                           # Trace the '+' function
      -> +
      : +
      -> (@ ($ + @ (pass $385455126)))       # Modified for tracing
      : (untrace '+)                         # Untrace '+'
      -> +
      : +
      -> 67319120                            # Back to original form

`(up [cnt] sym ['val]) -> any`
  Looks up (or modifies) the `cnt`'th previously saved value of `sym` in the corresponding enclosing environment. If `cnt` is not given, 1 is used. It is allowed to omit the `sym` argument, then the corresponding expression (function or method call) is returned. See also `eval`, `run`, `trail` and `env`.

      : (let N 1 ((quote (N) (println N (up N))) 2))
      2 1
      -> 1
      : (let N 1 ((quote (N) (println N (up N) (up N 7))) 2) N)
      2 1 7
      -> 7

      : (de foo (N)
         (println (up))
         (inc N) )
      -> foo
      : (foo 7)
      (foo 7)
      -> 8

`(upd sym ..) -> lst`
  Synchronizes the internal state of all passed (external) symbols by passing them to `wipe`. `upd` is the standard function passed to `commit` during database `transactions`.

      (commit 'upd)  # Commit changes, informing all sister processes

`(upp? 'any) -> sym | NIL`
  Returns `any` when the argument is a string (symbol) that starts with an uppercase character. See also `uppc` and `low?`

      : (upp? "A")
      -> "A"
      : (upp? "a")
      -> NIL
      : (upp? 123)
      -> NIL
      : (upp? ".")
      -> NIL

`(uppc 'any) -> any`
  Upper case conversion: If `any` is not a symbol, it is returned as it is. Otherwise, a new transient symbol with all characters of `any`, converted to upper case, is returned. See also `lowc`, `fold` and `upp?`.

      : (uppc 123)
      -> 123
      : (uppc "abc")
      -> "ABC"
      : (uppc 'car)
      -> "CAR"

`(use sym . prg) -> any`
`(use (sym ..) . prg) -> any`
  Defines local variables. The value of the symbol `sym` - or the values of the symbols `sym` in the list of the second form - are saved, `prg` is executed, then the symbols are restored to their original values. During execution of `prg`, the values of the symbols can be temporarily modified. The return value is the result of `prg`. See also `bind`, `job` and `let`.

      : (setq  X 123  Y 456)
      -> 456
      : (use (X Y) (setq  X 3  Y 4) (* X Y))
      -> 12
      : X
      -> 123
      : Y
      -> 456

`(useKey 'sym 'cls ['hook]) -> num`
  Generates or reuses a key for a database tree, by randomly trying to locate a free number. See also `genKey`.

      : (maxKey (tree 'nr '+Item))
      -> 8
      : (useKey 'nr '+Item)
      -> 12

`(usec ['flg]) -> num`
  Returns a number of microseconds. If `flg` is non-`NIL`, the microsecond fraction of the last call to `time` is returned, otherwise the number of microseconds since interpreter startup. See also `date`.

      : (usec)
      -> 1154702479219050
      : (list (date (date)) (time (time T)) (usec T))
      -> ((2013 1 4) (10 12 39) 483321)