apply(n) [osx man page]
apply(n) Tcl Built-In Commands apply(n) __________________________________________________________________________________________________________________________________________________ NAME
apply - Apply an anonymous function SYNOPSIS
apply func ?arg1 arg2 ...? _________________________________________________________________ DESCRIPTION
The command apply applies the function func to the arguments arg1 arg2 ... and returns the result. The function func is a two element list {args body} or a three element list {args body namespace} (as if the list command had been used). The first element args specifies the formal arguments to func. The specification of the formal arguments args is shared with the proc com- mand, and is described in detail in the corresponding manual page. The contents of body are executed by the Tcl interpreter after the local variables corresponding to the formal arguments are given the val- ues of the actual parameters arg1 arg2 .... When body is being executed, variable names normally refer to local variables, which are cre- ated automatically when referenced and deleted when apply returns. One local variable is automatically created for each of the function's arguments. Global variables can only be accessed by invoking the global command or the upvar command. Namespace variables can only be accessed by invoking the variable command or the upvar command. The invocation of apply adds a call frame to Tcl's evaluation stack (the stack of frames accessed via uplevel). The execution of body pro- ceeds in this call frame, in the namespace given by namespace or in the global namespace if none was specified. If given, namespace is interpreted relative to the global namespace even if its name does not start with "::". The semantics of apply can also be described by: proc apply {fun args} { set len [llength $fun] if {($len < 2) || ($len > 3)} { error "can't interpret "$fun" as anonymous function" } lassign $fun argList body ns set name ::$ns::[getGloballyUniqueName] set body0 { rename [lindex [info level 0] 0] {} } proc $name $argList ${body0}$body set code [catch {uplevel 1 $name $args} res opt] return -options $opt $res } EXAMPLES
This shows how to make a simple general command that applies a transformation to each element of a list. proc map {lambda list} { set result {} foreach item $list { lappend result [apply $lambda $item] } return $result } map {x {return [string length $x]:$x}} {a bb ccc dddd} -> 1:a 2:bb 3:ccc 4:dddd map {x {expr {$x**2 + 3*$x - 2}}} {-4 -3 -2 -1 0 1 2 3 4} -> 2 -2 -4 -4 -2 2 8 16 26 The apply command is also useful for defining callbacks for use in the trace command: set vbl "123abc" trace add variable vbl write {apply {{v1 v2 op} { upvar 1 $v1 v puts "updated variable to "$v"" }}} set vbl 123 set vbl abc SEE ALSO
proc(n), uplevel(n) KEYWORDS
argument, procedure, anonymous function Tcl apply(n)
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proc(n) Tcl Built-In Commands proc(n) __________________________________________________________________________________________________________________________________________________ NAME
proc - Create a Tcl procedure SYNOPSIS
proc name args body _________________________________________________________________ DESCRIPTION
The proc command creates a new Tcl procedure named name, replacing any existing command or procedure there may have been by that name. Whenever the new command is invoked, the contents of body will be executed by the Tcl interpreter. Normally, name is unqualified (does not include the names of any containing namespaces), and the new procedure is created in the current namespace. If name includes any namespace qualifiers, the procedure is created in the specified namespace. Args specifies the formal arguments to the procedure. It consists of a list, possibly empty, each of whose elements specifies one argument. Each argument specifier is also a list with either one or two fields. If there is only a single field in the specifier then it is the name of the argument; if there are two fields, then the first is the argu- ment name and the second is its default value. When name is invoked a local variable will be created for each of the formal arguments to the procedure; its value will be the value of corresponding argument in the invoking command or the argument's default value. Arguments with default values need not be specified in a procedure invocation. However, there must be enough actual arguments for all the formal arguments that don't have defaults, and there must not be any extra actual arguments. There is one special case to permit procedures with variable numbers of arguments. If the last formal argument has the name args, then a call to the procedure may contain more actual arguments than the procedure has formals. In this case, all of the actual arguments starting at the one that would be assigned to args are combined into a list (as if the list command had been used); this combined value is assigned to the local variable args. When body is being executed, variable names normally refer to local variables, which are created automatically when referenced and deleted when the procedure returns. One local variable is automatically created for each of the procedure's arguments. Global variables can only be accessed by invoking the global command or the upvar command. Namespace variables can only be accessed by invoking the variable command or the upvar command. The proc command returns an empty string. When a procedure is invoked, the procedure's return value is the value specified in a return command. If the procedure doesn't execute an explicit return, then its return value is the value of the last command executed in the pro- cedure's body. If an error occurs while executing the procedure body, then the procedure-as-a-whole will return that same error. SEE ALSO
info(n), unknown(n) KEYWORDS
argument, procedure Tcl proc(n)