Import Tcl-core 8.6.6 (as of svn r86089)

doc/apply.n

@@ -0,0 +1,102 @@
+'\"
+'\" Copyright (c) 2006 Miguel Sofer
+'\" Copyright (c) 2006 Donal K. Fellows
+'\"
+.TH apply n "" Tcl "Tcl Built-In Commands"
+.so man.macros
+.BS
+'\" Note:  do not modify the .SH NAME line immediately below!
+.SH NAME
+apply \- Apply an anonymous function
+.SH SYNOPSIS
+\fBapply \fIfunc\fR ?\fIarg1 arg2 ...\fR?
+.BE
+.SH DESCRIPTION
+.PP
+The command \fBapply\fR applies the function \fIfunc\fR to the arguments
+\fIarg1 arg2 ...\fR and returns the result.
+.PP
+The function \fIfunc\fR is a two element list \fI{args body}\fR or a three
+element list \fI{args body namespace}\fR (as if the
+\fBlist\fR command had been used).
+The first element \fIargs\fR specifies the formal arguments to
+\fIfunc\fR. The specification of the formal arguments \fIargs\fR
+is shared with the \fBproc\fR command, and is described in detail in the
+corresponding manual page.
+.PP
+The contents of \fIbody\fR are executed by the Tcl interpreter
+after the local variables corresponding to the formal arguments are given
+the values of the actual parameters \fIarg1 arg2 ...\fR.
+When \fIbody\fR is being executed, variable names normally refer to
+local variables, which are created automatically when referenced and
+deleted when \fBapply\fR returns.  One local variable is automatically
+created for each of the function's arguments.
+Global variables can only be accessed by invoking
+the \fBglobal\fR command or the \fBupvar\fR command.
+Namespace variables can only be accessed by invoking
+the \fBvariable\fR command or the \fBupvar\fR command.
+.PP
+The invocation of \fBapply\fR adds a call frame to Tcl's evaluation stack
+(the stack of frames accessed via \fBuplevel\fR). The execution of \fIbody\fR
+proceeds in this call frame, in the namespace given by \fInamespace\fR or
+in the global namespace if none was specified. If given, \fInamespace\fR is
+interpreted relative to the global namespace even if its name does not start
+with
+.QW :: .
+.PP
+The semantics of \fBapply\fR can also be described by:
+.PP
+.CS
+proc apply {fun args} {
+    set len [llength $fun]
+    if {($len < 2) || ($len > 3)} {
+         error "can't interpret \e"$fun\e" 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
+}
+.CE
+.SH EXAMPLES
+.PP
+This shows how to make a simple general command that applies a transformation
+to each element of a list.
+.PP
+.CS
+proc map {lambda list} {
+    set result {}
+    foreach item $list {
+        lappend result [\fBapply\fR $lambda $item]
+    }
+    return $result
+}
+map {x {return [string length $x]:$x}} {a bb ccc dddd}
+      \fI\(-> 1:a 2:bb 3:ccc 4:dddd\fR
+map {x {expr {$x**2 + 3*$x - 2}}} {-4 -3 -2 -1 0 1 2 3 4}
+      \fI\(-> 2 -2 -4 -4 -2 2 8 16 26\fR
+.CE
+.PP
+The \fBapply\fR command is also useful for defining callbacks for use in the
+\fBtrace\fR command:
+.PP
+.CS
+set vbl "123abc"
+trace add variable vbl write {\fBapply\fR {{v1 v2 op} {
+    upvar 1 $v1 v
+    puts "updated variable to \e"$v\e""
+}}}
+set vbl 123
+set vbl abc
+.CE
+.SH "SEE ALSO"
+proc(n), uplevel(n)
+.SH KEYWORDS
+anonymous function, argument, lambda, procedure,
+'\" Local Variables:
+'\" mode: nroff
+'\" End: