# Graph Style Script reference guide

The main building blocks of Graph Style Script (GSS) are expressions and directives. GSS files are a sequence of expressions and directives.

## Expressions​

Expressions are used to combine values to create new values using functions. For example, the expression:

Add(2, 5)  -> 7

creates a new value 7 from values 2 and 5. There are a lot of functions built into Graph Style Script so there are even more ways to combine values. There is even a function to create new functions.

When expressions are evaluated, values are created. There are several types of Graph Style Script values: Boolean, Color, Number, String, Array, Dictionary, Functionand Null.

An expression can be either literal expressions, name expressions or function applications. Literal expressions exist for Colors, Numbers and Strings.

This is a literal expression for Strings.

"Hello"  -> Hello

It evaluates to the value "Hello" of the type String. The newline character and double quotes can be escaped in strings using \ (backslash).

"In the end he said: \"I am Iron Man!\""  -> In the end he said: "I am Iron Man!"

These are literal expressions for Numbers.

123  -> 1233.14159  -> 3.14159

Literal expressions for colors are hex strings starting with '#'. This is a literal expression for the color red.

#ff0000  -> #ff0000

Name expressions are names that can be evaluated if there are values bound to them in the environment (lexical scope). Names can start with any of the lower case or upper case letters of the English alphabet and apart from those can contain digits and the following characters: -, _. Names can be defined using the Define function.

Define(superhero, "Iron Man")superhero  -> Iron Man

In the previous example the value "Iron Man" was bound to the name superhero. After that name expression superhero evaluates the value "Iron Man" to type String.

There are many built-in names that are bound to useful values. Most used are boolean values which are bound to True and False and null value which is bound to Null. Also, all the CSS web colors are bound to their names.

dodgerblue  -> #1e90ffforestgreen  -> #228b22

The third type of expressions are function application expressions. A function can be applied to the list of expressions (arguments) in the following way.

Concat("Agents", " ", "of", " ", "S.H.I.E.L.D.")  -> Agents of S.H.I.E.L.D.

Here the function Concat was applied to the list of string literal expressions to produce their concatenation. Any expression can be an argument.

Not all expressions have to be evaluated. For example, when calling If function one argument will not be evaluated.

Define(mood, "happy")Define(name, "Happy Hogan")If(Equals(mood, "happy"),   Format("{} is happy today.", name),   Format("{} is not happy today.", name))  -> Happy Hogan is happy today.

In the previous example expression Format("{} is not happy today", name) will not be evaluated because its value is not needed.

Some other function will not evaluate their arguments because they are interested in their names and not values. For example, when creating a new function argument names aren't evaluated, but are remembered to be later bound to the function arguments when the function is called.

Define(square, Function(x, Mul(x, x)))square(2)  -> 4

In the previous example the name x isn't evaluated in the first line, and neither is the expression Mul(x, x). In the second line when the function square is called number 2 will be bound to the name x and only then will Mul(x, x) be evaluated.

## Directives​

Directives are the second building block of style script. Directive names start with '@'. The name is followed by the optional expression (filter) which is followed by an opening curly brace, directive body and a closing curly brace. The directive body is a list of pairs of property names and expressions. Property names and expressions are separated by a colon and after every expression, a new line must follow. The directive structure is the following.

@<DirectiveName> <expression> {  <property-name-1>: <expression-1>  ...  ...  <property-name-n>: <expression-n>}

Like in CSS, directives defined later override properties of the previous directives.

Graph Style Script currently has four directives:

• @NodeStyle - for defining the visual style of graph nodes.
• @EdgeStyle - for defining the visual style of graph relationships.
• @ViewStyle - for defining the general graph style properties.
• @ViewStyle.Map - for defining the graph style properties when map is in the background.

An example of a directive is @NodeStyle directive which can be used to specify style properties of a graph node.

@NodeStyle {  border-width: 2  color: #abcdef  label: "Hello, World!"}

### @NodeStyle​

The @NodeStyle directive is used for defining style properties of a graph node. It is possible to filter the nodes to which the directive applies by providing an optional predicate after the directive name and before the opening curly brace.

Before any expressions are evaluated (including the predicate) the name node is bound to the graph node for which the directive is being evaluated. Graph node is of type Dictionary and has all information about the node (properties, labels).

Here is an example of a @NodeStyle directive that is applied to all graph nodes with the label superhero:

@NodeStyle HasLabel(node, vehicle) {  label: Format("{}, horsepower: {}",                Property(node, "model"),                Property(node, "horsepower"))}

The predicate can be any expression that returns a value of type Boolean. It should depend on node, because if it doesn't, it will either be applied to all nodes or to no nodes.

@NodeStyle And(HasProperty(node, "name"),               Equals(Property(node, "name"), "Tony Stark")) {  color: gold  shadow-color: red  label: "You know who I am"}

Take a look at the GSS @NodeStyle directive properties page to see all node styling possibilities.

### @EdgeStyle​

The @EdgeStyle directive is used for defining the style properties of a graph relationship. Most things work like the @NodeStyle directive with one exception: the directive will bind the name edge to the relationship for which the directive is being evaluated (@NodeStyle binds the name node).

Take a look at the GSS @EdgeStyle directive properties page to see all relationship styling possibilities.

### @ViewStyle​

@ViewStyle directive is used for defining style properties of a general graph view: link distance, view, physics, repel force, etc. It is also possible to use a predicate expression which acts as a filter to apply the defined properties to the final directive output.

@ViewStyle <predicate expression> {  <property-name-1>: <value expression-1>  ...  <property-name-n>: <value expression-n>}

Similar to @NodeStyle and @EdgeStyle, @ViewStyle has a built-in variable graph which can be used for directive filter or property assignment.

An example below shows a general directive style definition and a directive where style properties will only be applied if there are more than 10 nodes in the graph.

@ViewStyle {  collision-radius: 15  physics-enabled: True}@ViewStyle Greater(NodeCount(graph), 10) {  physics-enabled: False  repel-force: -300}

If there are less than 10 nodes in the graph, the final default graph style properties will be:

{  "collision-radius": 15,  "physics-enabled": true}

Otherwise, if there are more than 10 nodes in the graph, the final default graph style properties will be:

{  "collision-radius": 15,  "physics-enabled": false,  "repel-force": -300}

Take a look at the GSS @ViewStyle directive properties page to see all styling possibilities.

### @ViewStyle.Map​

@ViewStyle.Map directive is a subset of @ViewStyle because it defines additional style properties for a graph view when there is a map background. The map view will be available only if:

• @ViewStyle contains a property view set to value "map".
• There is at least one node with defined latitude and longitude properties

It is also possible to use a predicate expression which acts as a filter to apply the defined properties to the final directive output.

@ViewStyle.Map <predicate expression> {  <property-name-1>: <value expression-1>  ...  <property-name-n>: <value expression-n>}

Similar to @ViewStyle, @ViewStyle.Map also has a built-in variable graph which can be used for directive filter or property assignment.

An example below shows a general directive style definition and a directive where style properties will be only applied if there are more than 10 nodes in the graph.

@ViewStyle {  view: "map"}@ViewStyle.Map {  tile-layer: "detailed"}@ViewStyle.Map Greater(NodeCount(graph), 10) {  tile-layer: "dark"}

If there are less than 10 nodes in the graph, the final map graph style properties will be:

{  "tile-layer": "detailed"}

Otherwise, if there are more than 10 nodes in the graph, the final map graph style properties will be:

{  "tile-layer": "dark"}

Take a look at the GSS @ViewStyle.Map directive properties page to see all styling possibilities.

## Built-in functions​

Graph Style Script has a large number of built-in functions that can help you with achieving the right style for your graph. Take a look at the list of GSS built-in functions.

## Built-in colors​

Graph Style Script comes with built-in colors that you can use the color's name. Take a look at the list of built-in colors.

## Built-in variables​

Graph Style Script has a few built-in variables that you can use: node, edge, and graph. Read more about it in the list of built-in variables.

## File Structure​

Style script files are composed of expressions and directives. All expressions outside directives are evaluated first in the global environment. This is useful for defining names using function Define. After that @NodeStyle and @EdgeStyle directives are evaluated for each node and relationship, respectively. All the names in the global environment are visible while applying the directives so they can be used for defining property values inside directives.

For example:

Define(square, Function(x, Mul(x, x)))Define(maxAllowedDebt, 10000)@NodeStyle HasLabel(node, "BankUser") {  size: square(Property(node, "debt"))  color: If(Greater(Property(node, "debt"), maxAllowedDebt),            red,            lightblue)}

Names square and maxAllowedDebt are visible inside @NodeStyle directive.