Functions

Carina provides built-in functions for common operations and lets you define your own functions. This guide covers both, along with the pipe and compose operators.

Built-in functions

String functions

Function	Signature	Description
upper	upper(string) -> String	Converts to uppercase
lower	lower(string) -> String	Converts to lowercase
trim	trim(string) -> String	Removes leading/trailing whitespace
replace	replace(search, replacement, string) -> String	Replaces all occurrences
split	split(separator, string) -> list(String)	Splits string into a list
join	join(separator, list) -> String	Joins list elements into a string

Examples:

awscc.ec2.Vpc {
  cidr_block = '10.0.0.0/16'

  tags = {
    Name = upper('my-vpc')              # 'MY-VPC'
    Env  = replace('_', '-', 'my_env')  # 'my-env'
    Id   = join('-', ['vpc', 'prod'])    # 'vpc-prod'
  }
}

Collection functions

Function	Signature	Description
length	length(list | map | String) -> Int	Returns element/character count
concat	concat(items, base_list) -> list(Any)	Appends items to a list
flatten	flatten(list) -> list(Any)	Flattens nested lists by one level
keys	keys(map) -> list(String)	Returns map keys as a sorted list
values	values(map) -> list(Any)	Returns map values sorted by key
lookup	lookup(map, key, default) -> Any	Looks up a key with a fallback
map	map(accessor, collection) -> list(Any) | map(Any)	Extracts a field from each element

Examples:

let parts1 = ['web', 'test']
let parts2 = ['vpc']

awscc.ec2.Vpc {
  cidr_block = '10.0.0.0/16'

  tags = {
    Name = join('-', concat(parts2, parts1))  # 'web-test-vpc'
  }
}

Numeric functions

Function	Signature	Description
min	min(a, b) -> Number	Returns the smaller value
max	max(a, b) -> Number	Returns the larger value

Network functions

Function	Signature	Description
cidr_subnet	cidr_subnet(prefix, newbits, netnum) -> Ipv4Cidr	Calculates a subnet CIDR block

Example:

let vpcs = for (i, env) in ['dev', 'stg'] {
  awscc.ec2.Vpc {
    cidr_block = cidr_subnet('10.0.0.0/8', 8, i)
    # i=0 -> '10.0.0.0/16', i=1 -> '10.1.0.0/16'

    tags = {
      Name = "vpc-${env}"
    }
  }
}

Environment and security functions

Function	Signature	Description
env	env(name) -> string	Reads an environment variable
secret	secret(value) -> secret	Marks a value as secret (stored as hash in state)
decrypt	decrypt(ciphertext, key?) -> string	Decrypts using the provider’s encryption service (e.g., AWS KMS)

User-defined functions

Define reusable logic with the fn keyword:

fn tag_name(env: String, service: String): String {
  join('-', [env, service, 'vpc'])
}

awscc.ec2.Vpc {
  cidr_block = '10.0.0.0/16'

  tags = {
    Name = tag_name('production', 'web')  # 'production-web-vpc'
  }
}

Function syntax

fn name(param1: type1, param2: type2): return_type {
  expression
}

• Parameters can have type annotations (: String, : Int, etc.)
• Return type annotation is optional (: String)
• The function body is a single expression (the return value)

Local variables in functions

Functions can have local let bindings before the final expression:

fn subnet_name(env: String, tier: String, index: Int): String {
  let prefix = join("-", [env, tier])
  "${prefix}-${index}"
}

Default parameter values

Parameters can have default values:

fn make_tags(name: String, env: String = 'dev'): map(String) {
  {
    Name        = name
    Environment = env
  }
}

Pipe operator

The pipe operator |> passes the result of the left side as the last argument to the function on the right (data-last convention):

# Without pipe
let result = join('-', split('_', upper('hello_world')))

# With pipe -- reads left to right
let result = 'hello_world' |> upper() |> split('_') |> join('-')
# Result: 'HELLO-WORLD'

The pipe operator is especially useful with collection functions:

let names = ['web', 'api', 'worker']

# Extract and transform
let result = names |> join(', ')

Compose operator

The compose operator >> creates a new function by chaining two partially applied functions (closures). Both sides must be closures:

# split('_') is a closure (1 of 2 args provided)
# join('-') is a closure (1 of 2 args provided)
let transform = split('_') >> join('-')

The resulting function applies the left function first, then passes the result to the right function.

Partial application

When you call a built-in function with fewer arguments than it expects, you get a closure — a partially applied function that waits for the remaining arguments:

# replace expects 3 args; giving 2 returns a closure
let dashify = replace('_', '-')

# The closure is called when the last argument arrives (via pipe)
let result = 'hello_world' |> dashify()  # 'hello-world'

This works naturally with the pipe operator, since the piped value fills in the last argument.