Functions in Taxi

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Overview

Taxi provides support for declaring functions that can manipulate data.

Taxi itself does not provide implementations of these functions - it’s down to individual runtimes, such as Orbital.

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Declaring functions

Functions are declared as follows:

namespace com.foo {
   declare function concat(String,String):String
}

This declares a function named com.foo.concat, which accepts two String arguments, and returns a String.

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Parameter names

Parameters may be optionally declared with parameter names:

namespace com.foo {
   declare function concat(first: String,second: String):String
}

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Vararg parameters

The final parameter in a function may be declared as vararg by providing a trailing ...

namespace com.foo {
   // values is vararg, and can accept multiple values
   declare function concat(something: Int, values:String...):String
}

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Using functions

As with all other references, functions must be imported to be used, or referred to using their fully qualified name

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Functions in fields

Functions can be used in expressions on models by declaring using a by operator:

import com.foo.concat

model Person {
   firstName : FirstName inherits String
   lastName : LastName inherits String
   fullName : FullName inherits String by concat(FirstName, ' ', LastName)
}

As with all expressions, parameters are passed either by Type reference, or Field reference:

import com.foo.concat

model Person {
   firstName : FirstName inherits String
   lastName : LastName inherits String
   // By default references are assessed as lookups by type.
   fullName : FullName inherits String = concat(FirstName, ' ', LastName)
   // When prefixed by 'this.', lookups are assessed against field names
   formalName : String = concat(this.lastName, ', ', this.firstName)
}

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Functions in expression types

Functions may also be used in expression types. When functions are referenced as a type, the underlying base type is optional, and can be inferred by the compiler

declare function concat(String...):String

// FullName inherits String, as that's
// the return type of `concat`
type FullName = concat(FirstName, ' ', LastName)

model Person {
   firstName : FirstName inherits String
   lastName : LastName inherits String
   fullName : FullName
}

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Lambda functions

Taxi has support for declaring lambda functions - i.e., functions as parameters to another function.

declare function stringify(Int[], callback:(Int,String) -> String):String

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Generic types

Taxi has limited support for generic types in functions.

Type arguments may be before the function name:

declare function <T,A> reduce(T[], (T,A) -> A):A

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Taxi Stdlib

Taxi ships with a StdLib which contains a number of functions declared to assist with manipulating data.

Read the docs of the Taxi StdLib here