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+---
+title: More Inspections
+date: 2015-05-12
+tags: core, irb, cli-options
+---
+
+Some of IRB's command-line options can be called idiosyncratic as well. Take *math mode* as an example: It will require the infamous [mathn](https://github.com/ruby/ruby/blob/trunk/lib/mathn.rb) library on start up:
+
+    $ irb -m
+    >> Math #=> CMath
+    >> 3/2 #=> (3/2)
+    >> !!defined?(Vector) #=> true
+
+And another one surprised me: You can pass custom [inspectors](https://github.com/ruby/ruby/blob/trunk/lib/irb/inspector.rb) to IRB, for example, *yaml*:
+
+    $ irb -f --inspect yaml
+    >> [1,2,3]
+    => ---
+    - 1
+    - 2
+    - 3
+
+Or *marshal*:
+
+    $ irb -f --inspect marshal
+    >> 42
+    => i/
+
+But you can also define *your own inspectors on the fly*:
+
+    $ irb -f --inspect "{ |r| r.to_s.reverse }"
+    >> [1,2,3]
+    => ]3 ,2 ,1[
+
+It will be eval'd (!) as the block part of a new `proc`.
+
+
+## Resources
+
+- `man irb`
+- [Source: irb/context](https://github.com/ruby/ruby/blame/trunk/lib/irb/context.rb)
+- [Source: irb/inspectors](https://github.com/ruby/ruby/blob/trunk/lib/irb/inspector.rb)
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