[hack] utils: add `exists` and `for_all` to the signature of MyMap
[hack] utils: add `exists` and `for_all` to the signature of MyMap

Summary: better and more efficient than rewriting them with fold

Reviewed By: @int3

Differential Revision: D2433069

Eyyub/flow,darioajr/flow,JonathanUsername/flow,d14b3l/flow,OCamlPro/flow,shiftcars/flow,d14b3l/flow,d14b3l/flow,jamesgpearce/flow,jgrund/flow,jeffmo/flow,jamesgpearce/flow,jeffutter/flow,TiddoLangerak/flow,cesarandreu/flow,gabelevi/flow,graue/flow,nmote/flow,ForbesLindesay/flow,jdelStrother/flow,ylu1317/flow,facebook/flow,MichaelDeBoey/flow,darioajr/flow,samwgoldman/flow,Fresheyeball/flow,popham/flow,AprilArcus/flow,AprilArcus/flow,ForbesLindesay/flow,jeffutter/flow,AprilArcus/flow,JonathanUsername/flow,samwgoldman/flow,AprilArcus/flow,ylu1317/flow,danvk/flow,jdelStrother/flow,chenglou/flow,ForbesLindesay/flow,gabro/flow,danvk/flow,TiddoLangerak/flow,AgentME/flow,JohnyDays/flow,MichaelDeBoey/flow,TiddoLangerak/flow,fletcherw/flow,nmote/flow,nmote/flow,Fresheyeball/flow,jeffmo/flow,fletcherw/flow,samwgoldman/flow,JonathanUsername/flow,AgentME/flow,AgentME/flow,cesarandreu/flow,shiftcars/flow,gabro/flow,popham/flow,d14b3l/flow,chenglou/flow,mroch/flow,MichaelDeBoey/flow,Wanderfalke/flow,mroch/flow,jamesgpearce/flow,jeffmo/flow,jamesgpearce/flow,MichaelDeBoey/flow,KevinTCoughlin/flow,fletcherw/flow,shiftcars/flow,Fresheyeball/flow,JonathanUsername/flow,ylu1317/flow,popham/flow,AprilArcus/flow,shiftcars/flow,claudiopro/flow,JonathanUsername/flow,JonathanUsername/flow,chenglou/flow,gabelevi/flow,jamesgpearce/flow,claudiopro/flow,ForbesLindesay/flow,jgrund/flow,fletcherw/flow,gabelevi/flow,JonathanUsername/flow,jamesgpearce/flow,Wanderfalke/flow,popham/flow,danvk/flow,popham/flow,samwgoldman/flow,asivitz/flow,facebook/flow,AgentME/flow,jeffmo/flow,graue/flow,mcanthony/flow-type,shiftcars/flow,MichaelDeBoey/flow,facebook/flow,KevinTCoughlin/flow,KevinTCoughlin/flow,nmote/flow,Wanderfalke/flow,jdelStrother/flow,jdelStrother/flow,jgrund/flow,claudiopro/flow,gabelevi/flow,mroch/flow,graue/flow,gabro/flow,darioajr/flow,nmote/flow,samwgoldman/flow,gabelevi/flow,Eyyub/flow,asivitz/flow,facebook/flow,claudiopro/flow,gabro/flow,mroch/flow,JohnyDays/flow,facebook/flow,popham/flow,mroch/flow,jdelStrother/flow,OCamlPro/flow,mcanthony/flow-type,chenglou/flow,d14b3l/flow,mroch/flow,jeffutter/flow,jgrund/flow,facebook/flow,gabro/flow,jeffmo/flow,danvk/flow,cesarandreu/flow,gabelevi/flow,samwgoldman/flow,mcanthony/flow-type,gabelevi/flow,facebook/flow,chenglou/flow,OCamlPro/flow,jeffutter/flow,Wanderfalke/flow,claudiopro/flow,JohnyDays/flow,d14b3l/flow,mcanthony/flow-type,jdelStrother/flow,cesarandreu/flow,fletcherw/flow,ylu1317/flow,AprilArcus/flow,AgentME/flow,samwgoldman/flow,shiftcars/flow,nmote/flow,graue/flow,Eyyub/flow,popham/flow,jamesgpearce/flow,KevinTCoughlin/flow,darioajr/flow,jgrund/flow,gabro/flow,JohnyDays/flow,ForbesLindesay/flow,jeffmo/flow,TiddoLangerak/flow,nmote/flow,Fresheyeball/flow,jgrund/flow,OCamlPro/flow,mroch/flow,ylu1317/flow,asivitz/flow,chenglou/flow,graue/flow,fletcherw/flow,Eyyub/flow,ForbesLindesay/flow,TiddoLangerak/flow,asivitz/flow,graue/flow