Built-in Functions

XCL provides built-in functions for common operations on strings, collections, and other values. Functions are called with the standard name(arg1, arg2) syntax and can appear anywhere an expression is valid.

locals "s" {
    upper_name = upper(input.name)
    joined     = join(",", input.azs)
    tag_count  = len(input.tags)
}

The typechecker records function call expressions but does not validate function names or argument counts — that validation happens at the Pulumi Python runtime. Unrecognized function names produce runtime errors, not compile-time errors.

String functions

Function	Description
`upper(s)`	Convert string to uppercase
`lower(s)`	Convert string to lowercase
`trimspace(s)`	Strip leading and trailing whitespace
`trim(s, chars)`	Strip specified characters from both ends
`trimprefix(s, prefix)`	Remove prefix if present
`trimsuffix(s, suffix)`	Remove suffix if present
`replace(s, old, new)`	Replace all occurrences of `old` with `new`
`split(sep, s)`	Split string into a list on separator
`join(sep, list)`	Join list of strings with separator
`contains(s, substr)`	True if string contains substring
`startswith(s, prefix)`	True if string starts with prefix
`endswith(s, suffix)`	True if string ends with suffix
`format(fmt, args...)`	Printf-style string formatting
`substr(s, offset, length)`	Extract substring

Collection functions

Function	Description
`len(coll)`	Number of elements in a list, map, or string
`keys(m)`	List of map keys
`values(m)`	List of map values
`flatten(lists)`	Flatten a list of lists into one list
`distinct(list)`	Remove duplicate values
`sort(list)`	Sort list of strings or numbers
`reverse(list)`	Reverse a list
`concat(a, b)`	Concatenate two lists
`slice(list, start, end)`	Extract a sublist
`lookup(map, key, default)`	Look up map key with fallback
`merge(a, b)`	Merge two maps (b wins on collision)
`zipmap(keys, values)`	Create a map from parallel key/value lists
`toset(list)`	Convert list to set (deduplicate)
`tolist(set)`	Convert set to sorted list

Encoding functions

Function	Description
`jsonencode(value)`	Encode value as JSON string
`jsondecode(s)`	Decode JSON string to value
`base64encode(s)`	Base64-encode a string
`base64decode(s)`	Decode a base64 string
`urlencode(s)`	URL-encode a string

Numeric functions

Function	Description
`min(a, b)`	Minimum of two numbers
`max(a, b)`	Maximum of two numbers
`abs(n)`	Absolute value
`ceil(n)`	Round up
`floor(n)`	Round down
`pow(base, exp)`	Exponentiation

Type conversion functions

Function	Description
`tostring(v)`	Convert value to string
`tonumber(s)`	Parse string as number
`tobool(s)`	Parse string as boolean

Conditional / null helpers

Function	Description
`coalesce(vals...)`	Return first non-null value
`can(expr)`	Return true if expression evaluates without error

Usage in expressions

Functions compose naturally with other expressions:

locals "s" {
    // join a list of AZ names
    az_string = join(", ", input.azs)

    // uppercase environment prefix for resource names
    env_upper = upper(input.env)

    // derive bucket name from inputs
    bucket_name = lower(f"{input.project}-{input.env}-artifacts")

    // safe map lookup with default
    tier = lookup(input.tiers, input.env, "standard")
}

​String functions

​Collection functions

​Encoding functions

​Numeric functions

​Type conversion functions

​Conditional / null helpers

​Usage in expressions