How to use YAML.load with handlers - ruby

Question

irb(main):001:0> a="run: yes"
=> "run: yes"
irb(main):002:0> require 'yaml'
=> true
irb(main):003:0> YAML.load a
=> {"run"=>true}
irb(main):004:0> YAML.load(a, handlers => {'bool#yes' = identity})
SyntaxError: (irb):4: syntax error, unexpected '=', expecting =>
YAML.load(a, handlers => {'bool#yes' = identity})
^
from /usr/bin/irb:11:in `<main>
I want the yaml val is yes and i google find the handler will help.
But seems i do not use correct syntax.
I try to search related docs but fail.

Answer 1

The problems with the listed code are
that handlers isn't defined anywhere, you likely wanted :handlers
that identity isn't defined anywhere, maybe wanted :identity that
you are missing a > on your hash rocket (=>).
So to get this code to run it should (likely) look like
YAML.load("run: yes", :handlers => {'bool#yes' => :identity})
However, so far as I know the second parameter to YAML.load is a filename.
If you are able to change the input YAML, simply quoting the value "yes" will cause it come through as a string
YAML.load("a: 'yes'")
# => {"a"=>"yes"}
If you require the un-quoted string 'yes' in the YAML to be treated as 'yes', not true in ruby after parsing. I cobbled this together (with help from this question), using Psych::Handler and Pysch::Parser. Though I'm not sure if there's another easier/better way to do this without having to hack this all together like this.
require 'yaml'
class MyHandler < Psych::Handlers::DocumentStream
def scalar(value, anchor, tag, plain, quoted, style)
if value == 'yes'
super(value, anchor, tag, plain, true, style)
else
super(value, anchor, tag, plain, quoted, style)
end
end
end
def my_parse(yaml)
parser = Psych::Parser.new(MyHandler.new{|node| return node})
parser.parse yaml
false
end
my_parse("a: yes").to_ruby
# => {"a"=>"yes"}
my_parse("a: 'yes'").to_ruby
# => {"a"=>"yes"}
my_parse("a: no").to_ruby
# => {"a"=>false}
Sidenote in the console (and the source):
YAML
# => Psych