Settle on expression language

[nicpottier]

We use a library we built which is simple Excel inspired functions:
https://github.com/rapidpro/expressions

Our thoughts are basically just:

• no looping should be supported
• no complicated control structures
• but basic math / date / string functions are useful

[nicpottier]

Note that a chosen expression language is probably separate than how templating will be handled, but worth considering at the same time.

RapidPro does:

Hi @contact.name

Just because having only a leading character seems to be easier for users to grock (as opposed to ${contact.name} and lets us do decent completion. The more advanced case of:

Hi @(CAMELCASE(contact.name)) 

(to call a function) is slightly more awkward but also not used as often. (and still allows completion)

CC: @ericnewcomer @rowanseymour