add 'list-inspectors' & 'change-inspectors' commands.

the list-inspectors command shows a list of available inspectors as well
as the active inspectors in the list. inspectors are drawn with a name as
well as a short description.

change-inspector can be used to change the inspector by the name found in
the list-inspectors command.

an inspector in pry is something that prints a return value in a repl session.
i'm not crazy about the name `inspector` but the traditional name used in pry(`print`)
didn't fit well. some discussion led us to `inspector` for lack of a better word,
see #1176 on github for discussion

CHANGELOG.md

@@ -32,6 +32,10 @@
   - lists the available prompts available for use.
 * Add `change-prompt` command. (#1175)
   - switch the current prompt, by name.
+* Add `list-inspectors` command. (#1176)
+  - list the inspectors available to print ruby return values in a repl.
+* Add `change-inspector` command. (#1176)
+  - switch the current inspector, by name.
 
 #### Bug fixes, etc.
 * Move `Pry::BondCompleter` and bond integration to the [pry-bond](https://github.com/pry/pry-bond) rubygem. (#1166)

lib/pry.rb

@@ -168,3 +168,4 @@ require 'pry/rubygem'
 require "pry/indent"
 require "pry/last_exception"
 require "pry/prompt"
+require "pry/inspector"

lib/pry/commands/change_inspector.rb

@@ -0,0 +1,27 @@
+class Pry::Command::ChangeInspector < Pry::ClassCommand
+  match 'change-inspector'
+  group 'inspect'
+  description 'change the current pry inspector'
+  command_options argument_required: true
+  banner <<-BANNER
+    Usage: change-inspector
+    change the Proc to used to print return values in a repl session.
+    see list-inspectors for a list of available Proc's and a short description
+    of what they do.
+  BANNER
+
+  def process(inspector)
+    if inspector_map.key?(inspector)
+      _pry_.print = inspector_map[inspector][:value]
+      output.puts "switched to the '#{inspector}' inspector!"
+    else
+      raise Pry::CommandError, "'#{inspector}' isn't a known inspector!"
+    end
+  end
+
+private
+  def inspector_map
+    Pry::Inspector::MAP
+  end
+  Pry::Commands.add_command(self)
+end

lib/pry/commands/list_inspectors.rb

@@ -0,0 +1,34 @@
+class Pry::Command::ListInspectors < Pry::ClassCommand
+  match 'list-inspectors'
+  group 'inspect'
+  description 'list the inspector Procs available to use in pry'
+  banner <<-BANNER
+    Usage: list-inspectors
+    list the inspector Proc's available to print ruby objects(e.g: return values) in
+    a repl session.
+  BANNER
+
+  def process
+    output.puts heading("Available inspectors") + "\n"
+    inspector_map.each do |name, inspector|
+      output.write "name: #{text.bold(name)}"
+      output.puts selected_inspector?(inspector) ? selected_text : ""
+      output.puts inspector[:description]
+      output.puts
+    end
+  end
+
+private
+  def inspector_map
+    Pry::Inspector::MAP
+  end
+
+  def selected_text
+    text.red " (selected) "
+  end
+
+  def selected_inspector?(inspector)
+    _pry_.print == inspector[:value]
+  end
+  Pry::Commands.add_command(self)
+end

lib/pry/inspector.rb

@@ -0,0 +1,27 @@
+class Pry::Inspector
+  MAP = {
+    "default" => {
+      value: Pry::DEFAULT_PRINT,
+      description: <<-DESCRIPTION.each_line.map(&:lstrip!)
+        the default pry inspector. it has paging and color support, and uses pretty_inspect
+        when printing an object.
+      DESCRIPTION
+    },
+
+    "simple" => {
+      value: Pry::SIMPLE_PRINT,
+      description: <<-DESCRIPTION.each_line.map(&:lstrip)
+        a simple inspector that uses #puts and #inspect when printing an object.
+        it has no pager, color, or pretty_inspect support.
+      DESCRIPTION
+    },
+
+    "clipped" => {
+      value: Pry::CLIPPED_PRINT,
+      description: <<-DESCRIPTION.each_line.map(&:lstrip)
+        the clipped inspector has the same features as the 'simple' inspector but prints
+        large objects as a smaller string.
+      DESCRIPTION
+    }
+  }
+end