The procedure userinfo is used in Maple procedures to print useful information to the user.

The first argument lev is a non-negative integer which determines the infolevel setting at which information will be printed.

The second argument fn is a procedure name or set of procedure names for which this information is to be printed. The information will be printed if the global assignment infolevel[fn] := Lev; or infolevel[all] := Lev; was entered before invoking the procedure containing the userinfo statement, and $\mathrm{lev}\le \mathrm{Lev}$.

It is possible to have the name for which the information is printed different from the name of the procedure in which this information is given.  This is useful when writing a set of routines that work together.  You can set the infolevel for a set of routines at the same time.

If the third argument is the symbol 'NoName', this argument will be discarded and no function name will be printed. Otherwise, the name of the invoked procedure is printed using lprint, followed by a colon and 3 spaces.

If the third argument is a string containing one or more numbered of the form %n, %+n, %-n, or %{n|..|..|..} as also supported by the error command, WARNING function, and StringTools:-FormatMessage, then this string is interpreted as a format string in which the evaluated remaining arguments are substituted.

For details on the use of such parameters, refer to Error and Warning Message Formatting.

If the first remaining argument is not a format string as described above, then all the remaining arguments are evaluated and lprinted together, each separated from its neighbors by 3 spaces.

If an argument is of the form print(...) then that argument is prettyprinted.

If an argument is of the form lprint(...) then that argument is lprinted on a separate line.

The user must assign a non-negative integer to some of the entries in the global table infolevel before invoking the procedure.   If the entry infolevel[all] is a non-negative integer then every userinfo call will print if its level is less than or equal to infolevel[all] .

Throughout the Maple library userinfo statements have been used with the following conventions:

Level 1: reserved for information that the user must be told

Level 2,3: general information, including technique or algorithm being used

Level 4,5: more detailed information about how the problem is being solved

The item infolevel[hints] is initialized to a value 1. Maple sometimes returns unevaluated answers when it does not have enough information to produce an explicit answer (because, for example, such an answer would not be correct over all complex numbers). This facility is intended to report hints as to which further information, given through assume(), would enable Maple return an explicit answer.

The userinfo command is thread-safe as of Maple 15.

For more information on thread safety, see index/threadsafe.

a1 := proc(x,y) userinfo(3,a1,`entered with`,x,y); x+y end proc:

$\mathrm{infolevel}\left[\mathrm{a1}\right]≔3\:$

$\mathrm{a1}\left(3\,4\right)$

a1:   entered with   3   4

$7$

a2 := proc(x,y) userinfo(3,myname,`entered with`,x,y); x-y end proc:

$\mathrm{infolevel}\left[\mathrm{myname}\right]≔3\:$

$\mathrm{a2}\left(5\,2\right)$

a2:   entered with   5   2

$3$