gistfile1.txt

# Define has_cats as true
has_cats: [x]

# Same for has_dogs
has_dogs: [x]

# Define has_dinosaurs as false
has_dinosaurs: [_]

# Some expressions
nobody: !(use_cats | use_dogs)
nodejs_cats: has_cats & has_nodejs

# Mark experimental as unset
# To be defined in the runtime, for example,
# with Feature.set('expresimental', true)

experimental: [?]

# Expressions with uset values are allowed
expreimental_cats: has_cats & experimental

# Line doesn't end if the paren is opened
unstable_dogs: (
	[?]
	& has_dogs
	& !expreimental_cats
)

# Import all rules from ./base.features
# All relative filenames are resolved from _this_ file,
# not curdir
*: [from ./base.features]

# Import all rules from ./features.json, property "prod"
*: [json ./features.json prod]

# is_prod is true if env.ENV matches /^prod/
is_prod: [env ENV ^prod r]

# execute "which node" and return true if return code is 0
# (no error)
has_nodejs: [shell which node]

# Notice that nodejs_cats refers to has_nodejs, but
# has_nodejs is defined after that.
# That's perfectly fine.


# Operators

# & | ! ( )

# Functions

# [x] - true
# [_] - false
# [?] - is defined later

# [from str_filename] - import rules from file

# [json str_filename str_property? str_property? ...] - import rules (true/false/null) from json file

# [env str_varname str_matches str_flags?] - true if env variable matches
# str_flags: one of "", "r", "i", "ri"
# r stands for RegExp
# i stands for IgnoreCase

# Formal function syntax:
# function: "[" fn_name? (whitespace string)* "]"
# whitespace: <unicode whitespace range>
# fn_name: a-z* | "_" | "?"
# string: quoted_string | unquoted_string

# quoted_string: '"' quoted_string_char* '"' | "'" quoted_string_char* "'"
# quoted_string_char: <anything except whitespace and "\"> | escape-seq
# escape-seq: "\\" | "\r" | "\n" | "\t" | unicode-escape
# unicode-escape: "\u" escape_hex escape_hex escape_hex escape_hex
# escape-digit: 0 - 9 | a - f | A - F

# unquoted_string: unquoted_string_char+
# unquoted_string_char: <anything expect whitespace, "\", "[", "]">