security_monad.rb

db = [{name: "Jim", secret: "I peed my pants.", super_secret: "I love Nickleback."}]
user = {name: "Jim"}

get_secret = -> user { secret = db.find {|db_user| db_user[:name] == user[:name]}[:secret]; user.merge({secret: secret}) }
get_super_secret = -> user { super_secret = db.find {|db_user| db_user[:name] == user[:name]}[:super_secret]; user.merge({super_secret: super_secret}) }

bind = -> x, f { x[:secure] ? f[x[:value]].merge({secure: true}) : x } # security-aware manner of calling functions/methods
unit = -> n { {secure: false, value: n} }                              # makes objects security-aware
lift = -> f { -> x { unit[f[x]] } }                                    # makes functions/methods security-aware

securely_get_secret = lift[get_secret]
securely_get_super_secret = lift[get_super_secret]

# because of type-mismatch of doing things this way, we cannot do the following
securely_get_secret[{secure: true, value: user}]
securely_get_super_secret[{secure: true, value: user}]

# so we have to
bind[bind[{secure: true, value: user}, securely_get_secret], securely_get_super_secret]
bind[{secure: false, value: user}, securely_get_super_secret]

bind[unit[user], lift[get_secret]]

# Be aware that "security-aware" and "secure" are two different things

securely_get_secret[user] #=> returns {:secure=>false, :value=>{:name=>"Jim", :secret=>"I peed my pants."}}
bind[unit[user], securely_get_secret] #=> {:secure=>false, :value=>{:name=>"Jim"}}

# Only the bind function will enforce security rules.