ifc-expressions
v2.1.1
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Parsing and evaluation of IFC expressions
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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
- receiveExprEvalSuccessResult | 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 functiontoString(x)
for anyx
). - you have
REPLACE
, which only knows the wildcard character*
. (same forMATCHES, CONTAINS
) - you have
REGEXREPLACE
with full js Regular Expressions (same forREGEXMATCHES, 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'
, or17
- 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 quotesboolean
, e.g.TRUE
orfalse
: true or false, either spelled all-uppercase or all-lowercasenumeric
, e.g.1
or3.141
: a decimal number optionally containing one period to separate integer part from fractional partarray
, 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.