Whistle syntax

This page shows the general syntax to write a valid Whistle script.

Line structure

Whistle programs are divided into lines . Each line is a sequence of characters terminated by a NEWLINE ( \n ) token or an end-of-file ( EOF ) token.

The \n and \EOF tokens are automatically added to the end of each line when the Whistle program runs.

Whitespace

Whitespace characters in Whistle are spaces ( ), carriage returns ( \r ), and tabs ( \t ).

Comments

A comment begins with two forward slashes ( // ). It can be placed on its own line, at the beginning of a line, or at the end of a line. The Whistle mapping engine ignores the text after the beginning of the comment.

There's no specific convention for multiline comments, but you can create multiline comments using multiple single line comments. Whistle doesn't support inline comments.

Delimiters

The following table describes the delimiters for Whistle scripts.

;	Semicolon	An optional statement terminator. Semicolons are optional and can be placed at the end of a line, statement, or logical grouping of data.	Each example pair with and without semicolons behaves identically.

Identifiers

An identifier is a sequence of alphanumeric characters used as the name of a function, variable, field, or any other Whistle data type.

The underscore ( _ ) character can be used inside any identifier and as the first or last character in the identifier.

Basic identifiers

Basic identifiers are case-sensitive and must follow these requirements:

• They must begin with a letter, underscore ( _ ), or dollar sign ( $ ). Subsequent characters can be alphanumeric characters, dollar signs, and underscores.
• They must match the following regular expression: [$a-zA-Z_][$a-zA-Z_0-9]* .

Quoted identifiers

Quoted identifiers have the following properties:

• They can contain any UTF-8 character if the UTF-8 character is surrounded by single quotes ( '' ).
• Single quotes and backslashes ( \ ) inside strings must be escaped with a preceding backslash.
• They must match the following regular expression: '\'' ('\\\'' | ~['])+ '\'' .

Hybrid identifiers

Hybrid identifiers have the following properties:

• They can contain and begin with alphanumeric characters, dollar signs ( $ ), and underscores ( _ ).
• They can't begin with a number.
• They can contain any non-alphanumeric character, including spaces, but not including newlines. Non-alphanumeric characters can be in any position if the characters are escaped with a preceding backslash ( \ ).

Constants and literals

Numbers

The number constant consists of the following components, in order. A number doesn't need to use all the components.

1. An optional minus sign ( - ) to indicate a negative number.
2. One or more integers.
3. An optional decimal point ( . ) followed by a decimal value.

Numbers must meet the following requirements:

• They must match the following regular expression: -? [0-9]+ (. [0-9]+)? .
• They must fit into a 64-bit floating point value.

If a number containing a decimal is converted into a string, the decimal is removed if the decimal is considered negligible . A decimal is negligible if it's less than the united in last place (ULP) of the integer value.

Strings

Whistle has two types of strings: basic strings and interpolated strings .

Basic strings

Basic strings have the following properties:

• They can be zero or more UTF-8 characters enclosed in double quotes ( "" ).
• The double quote, backslash ( \ ), and brace ( { and } ) characters in a basic string must be escaped using a preceding backslash.

Interpolated strings

Interpolated strings have the following properties:

• They have the same requirements and limitations as a basic string, but allow expressions in the string that are evaluated and inserted. The resulting string is a combination of the original string and the string representation of the evaluated expression.
• They must be enclosed in brace {} characters.

Booleans

The boolean literal is expressed using the true and false constants.

Keywords

The following table shows the keywords in Whistle. A keyword is a word that's reserved by the language and has a special meaning. Keywords are case-sensitive.

Keywords marked with the ^* superscript can be used as identifiers . All other keywords are reserved and can't be used as identifiers.

and append * as def

else extend * false global

if import merge * option

or package replace * required

root side then true

var