ensemble: Add a simple ensemble command

Uses a prefix to automatically map from subcommand to
implementation.

Includes support for namespace ensemble

Signed-off-by: Steve Bennett <steveb@workware.net.au>

1 files changed, 36 insertions, 0 deletions

diff --git a/ensemble.tcl b/ensemble.tcl
new file mode 100644
index 0000000..9e87809
--- /dev/null
+++ b/ensemble.tcl
@@ -0,0 +1,36 @@
+# Implement the ensemble command
+
+proc ensemble {command args} {
+	set autoprefix "$command "
+	set badopts "should be \"ensemble command ?-automap prefix?\""
+	if {[llength $args] % 2 != 0} {
+		return -code error "wrong # args: $badopts"
+	}
+	foreach {opt value} $args {
+		switch -- $opt {
+			-automap { set autoprefix $value }
+			default { return -code error "wrong # args: $badopts" }
+		}
+	}
+	proc $command {subcmd args} {autoprefix {mapping {}}} {
+		if {![dict exists $mapping $subcmd]} {
+			# Not an exact match, so check for specials, then lookup normally
+			if {$subcmd in {-commands -help}} {
+				# Need to remove $autoprefix from the front of these
+				set prefixlen [string length $autoprefix]
+				set subcmds [lmap p [lsort [info commands $autoprefix*]] {
+					string range $p $prefixlen end
+				}]
+				if {$subcmd eq "-commands"} {
+					return $subcmds
+				}
+				set command [lindex [info level 0] 0]
+				return "Usage: \"$command command ... \", where command is one of: [join $subcmds ", "]"
+			}
+			# cache the mapping
+			dict set mapping $subcmd ${autoprefix}$subcmd
+		}
+		# tailcall here we don't add an extra stack frame, e.g. for uplevel
+		tailcall [dict get $mapping $subcmd] {*}$args
+	}
+}