functions [ {+|-}UkmtTuWz ] [ -x num ] [ name ... ]
functions -c oldfn newfn
functions -M [-s] mathfn [ min [ max [ shellfn ] ] ]
functions -M [ -m pattern ... ]
functions +M [ -m ] mathfn ...
       Equivalent to typeset -f, with the exception of the -c,  -x,  -M
       and  -W  options.   For  functions  -u and functions -U, see au-
       toload, which provides additional options.  For functions -t and
       functions -T, see typeset -f.

       The -x option indicates that any functions output will have each
       leading tab for indentation, added by the shell to show  syntac-
       tic  structure, expanded to the given number num of spaces.  num
       can also be 0 to suppress all indentation.

       The -W option turns on the option WARN_NESTED_VAR for the  named
       function  or  functions  only.   The option is turned off at the
       start of nested functions (apart from anonoymous functions)  un-
       less the called function also has the -W attribute.

       The  -c  option causes oldfn to be copied to newfn.  The copy is
       efficiently handled internally by reference counting.  If  oldfn
       was marked for autoload it is first loaded and if this fails the
       copy fails.  Either function may subsequently be redefined with-
       out  affecting  the other.  A typical idiom is that oldfn is the
       name of a library shell function which is then redefined to call
       newfn, thereby installing a modified version of the function.

       The -M and +M flags

       Use of the -M option may not be combined with any of the options
       handled by typeset -f.

       functions -M mathfn defines mathfn as the name of a mathematical
       function recognised in all forms  of  arithmetical  expressions;
       see  the  section `Arithmetic Evaluation' in zshmisc(1).  By de-
       fault mathfn may take any number of  comma-separated  arguments.
       If  min  is given, it must have exactly min args; if min and max
       are both given, it must have at least min and at most max  args.
       max may be -1 to indicate that there is no upper limit.

       By  default  the  function is implemented by a shell function of
       the same name; if shellfn is specified it gives the name of  the
       corresponding  shell function while mathfn remains the name used
       in arithmetical expressions.  The name of the function in $0  is
       mathfn  (not shellfn as would usually be the case), provided the
       option FUNCTION_ARGZERO is in effect.  The positional parameters
       in the shell function correspond to the arguments of the  mathe-
       matical function call.

       The  result of the last arithmetical expression evaluated inside
       the shell function gives the result of  the  mathematical  func-
       tion.   This  is  not limited to arithmetic substitutions of the
       form $((...)), but also includes arithmetical expressions evalu-
       ated in any other way, including by the let builtin, by  ((...))
       statements,  and  even  by  the return builtin and by array sub-
       scripts.  Therefore, care must be taken not to  use  syntactical
       constructs  that  perform arithmetic evaluation after evaluating
       what is to be the result of the function.  For example:

              # WRONG
              zmath_cube() {
                (( $1 * $1 * $1 ))
                return 0
              }
              functions -M cube 1 1 zmath_cube
              print $(( cube(3) ))

       This will print `0' because of the return.

       Commenting the return out would lead to a different problem: the
       ((...)) statement would become the last statement in  the  func-
       tion,  so  the  return  status  ($?)  of  the  function would be
       non-zero (indicating failure) whenever the arithmetic result  of
       the function would happen to be zero (numerically):

              # WRONG
              zmath_cube() {
                (( $1 * $1 * $1 ))
              }
              functions -M cube 1 1 zmath_cube
              print $(( cube(0) ))

       Instead, the true builtin can be used:

              # RIGHT
              zmath_cube() {
                (( $1 * $1 * $1 ))
                true
              }
              functions -M cube 1 1 zmath_cube
              print $(( cube(3) ))

       If  the additional option -s is given to functions -M, the argu-
       ment to the function is a single string:  anything  between  the
       opening  and matching closing parenthesis is passed to the func-
       tion as a single argument, even if it includes commas  or  white
       space.   The minimum and maximum argument specifiers must there-
       fore be 1 if given.  An empty  argument  list  is  passed  as  a
       zero-length string.  Thus, the following string function takes a
       single argument, including the commas, and prints 11:

              stringfn() { (( $#1 )); true }
              functions -Ms stringfn
              print $(( stringfn(foo,bar,rod) ))

       functions -M with no arguments lists all such user-defined func-
       tions in the same form as a definition.  With the additional op-
       tion  -m  and  a  list  of arguments, all functions whose mathfn
       matches one of the pattern arguments are listed.

       function +M removes the list of mathematical functions; with the
       additional option -m the arguments are treated as  patterns  and
       all  functions  whose  mathfn  matches  the pattern are removed.
       Note that the shell function implementing the behaviour  is  not
       removed (regardless of whether its name coincides with mathfn).
