Add examples of Metakit usage to examples/metakit.tcl

1 files changed, 112 insertions, 0 deletions

diff --git a/examples/metakit.tcl b/examples/metakit.tcl
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+package require mk
+
+# These will become subcommands of every view handle
+
+# Looping using cursors
+proc {mk.view each} {view arrayVar script} {
+    upvar 1 $arrayVar array
+    for {set cur $view!0} {[cursor valid $cur]} {cursor incr cur} {
+        set array [cursor get $cur]
+        uplevel 1 $script
+    }
+}
+
+# Shortcuts to avoid cursors for one-time operations
+proc {mk.view set} {view pos args} {
+    tailcall cursor set $view!$pos {*}$args
+}
+proc {mk.view append} {view args} {
+    tailcall cursor set $view!end+1 {*}$args
+}
+proc {mk.view insert} {view pos args} {
+    # Note that this only inserts fresh rows and doesn't set any data
+    tailcall cursor insert $view!$pos {*}$args
+}
+
+# Dump a view to stdout
+proc {mk.view dump} {view} {
+    $view each row {puts "  $row"}
+}
+
+# -----------------------------------------------------------------------------
+
+# Open an in-memory database
+set db [storage]
+
+# Specify the view structure, creating new views and restructuring existing
+# ones as necessary
+$db structure firstview  {key string first string}
+$db structure secondview {key string second string}
+
+# Open them.
+[$db view firstview] as fstview
+# Or equivalently (using pipeline notation)
+$db view secondview | as sndview
+
+# Use the helpers defined above to populate the first view
+$fstview set 0 key foo first bar
+$fstview append key hello first world
+$fstview insert 0
+$fstview set 0 key metakit first example
+
+# Or use cursors directly. A end-X/end+X cursor moves automatically when
+# the view size changes.
+set cur $sndview!end+1
+cursor set $cur key foo second baz
+cursor set $cur key hello second goodbye
+cursor set $cur key silly second examples
+
+puts "First view:"
+$fstview dump
+puts "Second view:"
+$sndview dump
+
+puts "\nNow trying view operations. Note that all the binary operations"
+puts "are left-biased when it comes to conflicting property values.\n"
+
+puts "Join on key:" ;# Common subset of the two outer joins below
+$fstview join $sndview key | dump
+puts "Outer join on key:" ;# Will yield more rows than an inner join
+$fstview join $sndview -outer key | dump
+puts "Outer join on key, in reverse order:"
+$sndview join $fstview -outer key | dump
+
+puts "Cartesian product:"
+$fstview product $sndview | dump
+
+puts "Pairing:"
+$fstview pair $sndview | dump
+puts "Pairing, in reverse order:"
+$sndview pair $fstview | dump
+
+puts "Complex pipeline (fetch rows 3,5,.. from the cartesian product and sort"
+puts "them on the 'first' property):"
+$fstview product $sndview | range 3 end 2 | sort first | dump
+# Slice step defaults to 1. Sorting may be performed on several properties at
+# a time, prepending a "-" (minus sign) will cause the sort order to be reversed.
+
+puts "Another one (fetch the unique key values from the cartesian product):"
+$fstview product $sndview | project key | unique | dump
+# Use "without" to remove certain properties.
+
+puts "Keys in the cartesian product not in the reverse pairing:"
+[$fstview product $sndview | project key | unique] minus [$sndview pair $fstview | unique] | dump
+# Union "union", intersection "intersect" and symmetric difference "different"
+# are also available. They all work only if the rows are unique.
+
+puts "Create a subview:"
+$fstview product $sndview | group subv key | as complexview | dump
+# Not so informative as subviews are not displayed properly. Several grouping
+# properties may be specified.
+puts "Get its values for row #0:"
+cursor get $complexview!0 subv | dump
+puts "And flatten it back:"
+$complexview flatten subv | dump
+
+puts "Remove a row:"
+cursor remove $sndview!1
+$sndview dump
+# Several rows may be removed at once by specifying a row count
+puts "Clear the view:"
+$sndview resize 0
+$sndview dump