Validation defines the rules that must hold in your language. These are not syntax rules but additional checks on the model or Abstract Syntax Tree (AST).

The validator definition provides the constraints or rules that should be true in the models built by your users. Any part of the validator definition must be included in a file with the extension .valid. All files with this extension in the defs folder (i.e. the folder containing your definition files) are combined into one validator definition.

Freon supports four types of validation rules.

A simple value rule defines constraints on the value of a single property. Given a simple property, its value can be restricted to a specified range or set of values.

// Insurance/src/defs/validator-extras.valid#L3-L6

EntityAttribute {
    self.numVal >= 12;       // in .ast file: "numVal: number;"
    self.numVal <= 30;
}

Given a list property, a not-empty rule can be stated. The rule is satisfied when the list contains at least one element.

An is-unique rule is another rule that can be stated for a list property. The rule is satisfied when the given property is unique within the list.

// Insurance/src/defs/validator-docu.valid#L3-L7

InsuranceProduct {
    notEmpty self.parts;
    in self.parts isunique name;
    in self.helpers isunique name;
}

Given a simple property of type identifier, a valid-identifier-rule can be given. The property complies with the rule if it is a valid identifier according to the TypeScript definition.

For a valid-identifier-rule the validIdentifier keyword is used followed by an optional simple property. When the property is present, this property is checked. If the property is omitted, Freon assumes and checks a default simple property named name of type identifier.

// Insurance/src/defs/validator-docu.valid#L27-L32

}
CalcFunction {
    // typecheck conformsTo (self.body, self.declaredType);
    in self.parameters isunique name;
    validIdentifier
    {

Based on the typing rules defined in the typer, rules can be stated to ensure type compliance. To indicate a type checking rule the keyword typecheck is used, followed by either equalsType or conformsTo. equalsType requires both properties to have identical types, while conformsTo allows the first to conform to the second.

In type checking rules it is possible to use predefined instances of a limited concept.

// Insurance/src/defs/validator-docu.valid#L10-L12

MinusExpression  {
    typecheck equalsType( self.left, self.right );
}

Generated error messages can be customized. Similar to the editor definition, properties can be used in the error message using the syntax ${propName}. Optionally, a severity level can be specified. The possible values are “error”, “warning”, “hint”, “improvement”, “todo”, and “info”. If omitted, the severity defaults to “todo”.

// Insurance/src/defs/validator-docu.valid#L28-L36

CalcFunction {
    // typecheck conformsTo (self.body, self.declaredType);
    in self.parameters isunique name;
    validIdentifier
    {
        message: "El nombre '${self.name}' no es un identificador correcto.",
        severity: error
    };
}

Freon automatically applies the following default validation rules:

• Non-optional properties must be set.
• Non-optional lists must contain at least one element.
• Any reference must resolve to an existing element.