user-defined functions

[anthony-c-martin]

Proposal - Functions

Goals

• Avoid code repetition both in-file and across files.

Non-goals

• The cross-file sharing syntax should be defined in the modules spec, so is not currently included here.

Spec

The function keyword provides a very simple mechanism for defining a pure function:

function <identifier>(<<arg> ,>*) {
    variable <name>: <value>
    ...

    return <output>
}

A function creates a new scope, and cannot reference any identifiers from an outer scope; the only identifiers initially available are those defined as arguments. The function body can consist of variable definitions to break things up, and the function must terminate with a return value. Other keywords such as resource, input and output are not supported inside a function.

A function body may access another user-defined function, or a built-in function, but no form of recursion is allowed.

Functions are not annotated with types, but types should be inferred where possible when the function is called.

Example

// defining the function
function getConnectionString(storageAccount) {
    variable primaryKey: storageAccount.listKeys().primary

    return 'DefaultEndpointsProtocol=http;AccountName=${storageAccount.name};AccountKey=${primaryKey};'
}

// calling the function
variable myConnectionString: getConnectionString(myAccount)

// this should throw a type error because the boolean type does not support `listKeys()`:
variable myConnectionString: getConnectionString(false)

[jongio]

Would love to have this for parameter validation.

[takekazuomi]

I want this for common naming rules across modules.