ifc-expressions

IFC Expressions

This project defines an expression language for IFC models. An expression is evaluated in the context of an element of the IFC model and a specific property of that element.

Interface

Two ways to interact with 'ifc-expression':

• evaluate an expression string directly - receive ExprEvalSuccessResult | ExprEvalError

or

• parse an expression - receive a IfcExpressionParseResult
• evaluate a IfcExpressionParseResult - receive ExprEvalSuccessResult | ExprEvalError

Usage

To connect ifc-expressions with your IFC model, you have to provide an implementation of src/context/IfcExpressionContext. Without such a context, the expressions that contain references to the model cannot be evaluated.

import {IfcExpression} from "ifc-expression";
import {IfcExpressionContext} from "./IfcExpressionContext";

const result = IfcExpression.evaluate("1 + 1"); // evaluation without context
console.log(JSON.stringify(result));
// ExprEvalSuccessObj {
//   status: 1000,
//   result: NumericValue {
//     value: 2
//   }
//}
const ctx: IfcExpressionContext = ... ; // set to your context here
const result2 = IfcExpression.evaluate("$element.property('width').value() * 2 ", ctx);

Quick Reference

Get the current property value:

$property.value()

Get the name of the property set the property is in:

$property.propertySet.name()

Get the name of the current element:

$element.name()

Get the name of the type of the current element:

$element.type().name()

Get value of property myProp from property set myPset in the current element:

$element.propertySet('myPset').property('myProp').value()

The last expression can also be written as

VALUE(PROPERTY(PROPERTY_SET($element, 'myPset'),'myProp'))

Check if property myProp exists in property set myPset in the current element:

$element.propertySet('myPset').property('myProp').exists()

Hints:

• Function/Method names are case-insensitive
• you have + - * / ^ for numerics
• you have && || >< ! for booleans (><is xor)
• you have == != >= <= > < for strings, booleans and numerics
• you have a .toString() method on anything (or, equivalently, a function toString(x) for any x ).
• you have REPLACE, which only knows the wildcard character *. (same for MATCHES, CONTAINS)
• you have REGEXREPLACE with full js Regular Expressions (same for REGEXMATCHES, REGEXCONTAINS)

IFC Expression Language Syntax

The project uses ANTLR4 for parsing. The grammar is in src/grammar/ifcExpression.g4.

The result of expression evaluation is a value of type string, numeric, boolean, ifcObjectRef, where ifcObjectRef is a reference to some object in the IFC model.

The language allows for specifying a single expression. There are no control statements and there is no way to define custom functions or custom types.

An expression can be

• a literal, such as 'hello world', or 17
• a variable reference, such as $property or $element,(for accessing the IFC model).

... or a combination of multiple expressions:

• a function call, such as REPLACE("hello world", "world", "friends")
• a function call in 'method-call style', such as "hello world".replace("world", "friends")
• a combination using operators, such as +, &&, ==

Types

• string, e.g. 'abc' or "abc": text enclosed in single or double quotes
• boolean, e.g. TRUE or false: true or false, either spelled all-uppercase or all-lowercase
• numeric, e.g. 1 or 3.141: a decimal number optionally containing one period to separate integer part from fractional part
• array, e.g. `[1,2,"hi there"]: an ordered list of expressions

Operators

• numeric operators
  • '+', '-', '*', '/': plus, minus, multiplication, division - with the ususal precedence rules and associativity
  • '^': raise to the power or, e.g. 2^3 (= 8)
• boolean operators
  • &&', ||, ><`: boolean and, or, xor
  • !: boolean not
• string operators
  • '+': string concatenation

Functions

comparison functions

equals(a,b), greaterThan(a,b), greaterThanOrEquals(a,b), lessThan(a,b), lessThanOrEqual(a,b)",

boolean operator functions

not(a), and(a,b), or(a,b), xor(a,b), implies(a,b)

string matching

contains(string, pattern), e.g. contains('hello world', 'he*o') returns true if the string contains the pattern. * matches any number of characters.

regexContains(string, regex), e.g. regexContains('hello, world', 'h[aeiou]ll[aeiou]+\\\s') returns true if the string contains the regular expression.

matches(string, pattern), e.g. matches('hello world', 'he*o') returns true if the whole string matches the pattern. * matches any number of characters.

regexMatches(string, regex), e.g. regexMatches('hello, world', 'h[aeiou]ll[aeiou]+\\\s') returns true if the whole string matches the regular expression.

string replacement

replace(string, pattern, replacement), e.g. replace('hello world', 'he*o', 'bye') returns the string, with all occurrences of the pattern replaced with replacement. * matches any number of characters.

regexReplace(string, regex, replacement), e.g. regexReplace('hello, world', 'h([aeiou]ll[aeiou]+) ', 'm$1w ') returns the string, with all occurrences of the regex replaced with replacement.

ifc object accessor functions

property(object: ifcPropertySetRef|ifcTypeObjectRef|ifcElementRef, name: string): returns an ifcPropertyRef or an error or an error if object has no property with that name

propertySet(object: ifcProperty): returns an ifcPropertySetRef

propertySet(object: ifcTypeObjectRef|ifcElementRef, name: string): returns an ifcPropertySetRef or an error if the element or type has no property set with that name.

type(object: ifcElementRef): returns an ifcTypeObjectRef or an error.

exists(object: ifcObjectRef): boolean check whether an object reference obtained by the above methods actually exists (suppresses the error they generate)

Translation and condition functions

map(input, mapping: [[in, out], [in, out], ... ], default): finds the first [in,out] pair in the specified mapping where in == input and returns that pair's out value. If none is found, default is returned.

if(condition, thenValue, elseValue): returns thenValue if condition is true, elseValue otherwise.

choose([[condition, out], [condition, out], ... ], default): finds the first [condition, out] pair where condition == true and returns its out value. In none is found, default is returned.