Release.1.5.1.adoc

Features

1. FFI: return value checking http://bucklescript.github.io/bucklescript/Manual.html#_unicode_support_since_1_5_1

2. FFI: Detect global variable existence http://bucklescript.github.io/bucklescript/Manual.html#_detect_global_varialbe_existence_code_bs_external_code_since_1_5_1

Minor breaking changes

1. changes NodeJS special variables from module_ to _module to make it more consistent

2. [%node ] return [_ option] type instead of undefined