JarCastingExpreTau
ExpreTau is a simple expression engine written in Java, of which the runtime codes are split from parsing and compiling codes. The classes in runtime are serializable so that they are suitable for runtime of distributed computing system, like Apache Flink.
ExpreTau is just "Expression" and "TAU". The idea of "TAU" is coming from The Tau Manifesto.
Getting Started
public class MyClass {
public Object calc() {
// The original expression string.
String exprString = "(1 + 2) * (5 - (3 + 4))";
// parse it into an Expr object.
Expr expr = ExpretauCompiler.INS.parse(exprString);
// Compile in a CompileContext (can be null without variables in the expression) and get an RtExpr object.
RtExpr rtExpr = expr.compileIn(null);
// Evaluate it in an EvalContext (can be null without variables in the expression).
return rtExpr.eval(null);
}
}
The RtExpr object can do eval multiple times in different EvalContext after generated by compileIn.
Module expretau_console can be simply used as a command line calculator, which is based on ExpreTau.
Dependencies
<?xml version="1.0" encoding="UTF-8"?>
<dependencies>
<!-- Required if you want to do parsing and compiling -->
<dependency>
<groupId>io.github.datacanvasio.expretau</groupId>
<artifactId>expretau-parser</artifactId>
<version>1.0.0</version>
</dependency>
<!-- Required if you want to do evaluating -->
<dependency>
<groupId>io.github.datacanvasio.expretau</groupId>
<artifactId>expretau-runtime</artifactId>
<version>1.0.0</version>
</dependency>
</dependencies>
Variables and Context
Variables can be used in expressions, but a CompileContext must be provided to define the types of variables.
A JSON Schema definition can be used as a source of CompileContext. For example (in YAML format for simplicity, but you can surely use JSON format)
type: object
properties:
a:
type: integer
b:
type: number
c:
type: boolean
d:
type: string
additionalProperties: false
where variables a, b, c, d are defined with specified types. The a RtExpr can be compiled as following,
public class MyClass {
public RtExpr compile(String jsonSchemaInYamlFormat) {
// jsonSchemaInYamlFormat can be a String/InputStream contains the JSON Schema definition.
RtSchemaRoot schemaRoot = SchemaParser.YAML.parse(jsonSchemaInYamlFormat);
Expr expr = ExpretauCompiler.INS.parse("a + b");
return expr.compileIn(schemaRoot.getSchema());
}
}
You can also create a parser with the RtSchemaRoot object to parse a JSON/YAML source into a EvalContext object.
public class MyClass {
public Object calc(RtSchemaRoot schemaRoot, RtExpr rtExpr) {
DataParser parser = DataParser.yaml().schema(schemaRoot);
// RtData implements EvalContext
RtData data = parser.parse("{a: 2, b: 3.0, c: true, d: foo}");
// The result should be a Double 5.0
return rtExpr.eval(data);
}
}
Nested Context
In a JSON Schema definition, objects and arrays can be nested into each other, for example,
type: object
properties:
a:
type: object
properties:
b:
type: number
c:
type: boolean
additionalProperties: false
d:
type: array
items:
- type: integer
- type: string
additionalItems: false
additionalProperties: false
In this context, you can use a.b and a.c to access the number and the boolean variables. The syntax looks the same as map index, but they are really separate variables. On the contrary, a is not an existing variable. Also, you can use d[0] and d[1] to access the integer and the string variables and d is not an existing variable.
The additionalProperties and additionalItems are crucial. If they are set to true (which is default in JSON Schema Specification), a becomes a variable of Map type and d of List type, which can be accessed by the same syntax, but the operating is a runtime indexing, not a var identifying in compiling time.
The special variable $ can be used to access the whole context, so $.a is the same as a. $ is useful for a context with an array as root. The parser also looks on a.b as a['b'], so the syntax to access variables is much like JSONPath.
Operators
| Category | Operator | Associativity |
|---|---|---|
| Parenthesis | ( ) |
|
| Function Call | ( ) |
Left to right |
| Name Index | . |
Left to right |
| Array Index | [ ] |
Left to right |
| Unary | + - |
Right to left |
| Multiplicative | * / |
Left to right |
| Additive | + - |
Left to right |
| Relational | < <= > >= == = != <> |
Left to right |
| String | startsWith endsWith contains matches |
Left to right |
| Logical NOT | ! not |
Left to right |
| Logical AND | && and |
Left to right |
| Logical OR | || or |
Left to right |
Data Types
| Type Name | JSON Schema Type | Hosting Java Type | Literal in Expression |
|---|---|---|---|
| Integer | java.lang.Integer | ||
| Long | integer | java.lang.Long | 0 20 -375 |
| Double | number | java.lang.Double | 2.0 -6.28 3e-4 |
| Boolean | boolean | java.lang.Boolean | true false |
| String | string | java.lang.String | "hello" 'world' |
| Decimal | java.math.BigDecimal | ||
| Time | java.util.Date | ||
| IntegerArray | java.lang.Integer[] | ||
| LongArray | array | java.lang.Long[] | |
| DoubleArray | array | java.lang.Double[] | |
| BooleanArray | array | java.lang.Boolean[] | |
| StringArray | array | java.lang.String[] | |
| DecimalArray | java.math.BigDecimal[] | ||
| ObjectArray | array | java.lang.Object[] | |
| List | array | java.util.List | |
| Map | object | java.util.Map | |
| Object | object | java.lang.Object |
For JSON Schema of type array, the final type is determined as in the following table.
Value of additionalItems |
Value of items.type |
Type Name |
|---|---|---|
false |
split into variables | |
true |
integer | LongArray |
true |
number | DoubleArray |
true |
boolean | BooleanArray |
true |
string | StringArray |
true |
object | ObjectArray |
true |
List |
For JSON Schema of type object, the final type is determined as in the following table.
Value of additionalProperties |
Value of properties |
Type Name |
|---|---|---|
false |
split into variables | |
true |
not null | Map |
true |
null | Object |
NOTE: Some types cannot be written literally in expressions, but they do exist in the engine. They can be got by pre-defined constants, variables or intermediate results.
Constants
| Name | Value |
|---|---|
| TAU | 6.283185307179586476925 |
| E | 2.7182818284590452354 |
There is not "3.14159265" but "TAU".
Functions
Mathematical
See Math (Java Platform SE 8).
| Function | Java function based on | Description |
|---|---|---|
abs(x) |
java.lang.Math.abs |
|
sin(x) |
java.lang.Math.sin |
|
cos(x) |
java.lang.Math.cos |
|
tan(x) |
java.lang.Math.tan |
|
asin(x) |
java.lang.Math.asin |
|
acos(x) |
java.lang.Math.acos |
|
atan(x) |
java.lang.Math.atan |
|
cosh(x) |
java.lang.Math.cosh |
|
sinh(x) |
java.lang.Math.sinh |
|
tanh(x) |
java.lang.Math.tanh |
|
log(x) |
java.lang.Math.log |
|
exp(x) |
java.lang.Math.exp |
Type conversion
| Function | Java function based on | Description |
|---|---|---|
int(x) |
Convert x to Integer |
|
long(x) |
Convert x to Long |
|
double(x) |
Convert x to Double |
|
decimal(x) |
Convert x to Decimal |
|
string(x) |
Convert x to String |
|
string(x, fmt) |
Convert x to String, x is a Time |
|
time(x) |
Convert x to Time |
|
time(x, fmt) |
Convert x to Time, x is a String |
String
See String (Java Platform SE 8).
| Function | Java function based on | Description |
|---|---|---|
toLowerCase(x) |
String::toLowerCase |
|
toUpperCase(x) |
String::toUpperCase |
|
trim(x) |
String::trim |
|
replace(x, a, b) |
String::replace |
|
substring(x, s) |
String::substring |
|
substring(x, s, e) |
String::substring |
User defined functions
It is simple to add an user defined function to ExpreTau.
First, define a class like
public class HelloOp extends RtFun {
private static final long serialVersionUID = -8060697833705004059L;
protected HelloOp(@Nonnull RtExpr[] paras) {
super(paras);
}
@Override
protected Object fun(@Nonnull Object[] values) {
return "Hello " + values[0];
}
@Override
public int typeCode() {
return TypeCode.STRING;
}
}
Then register it to the FunFactory
public class TestUdf() {
@Test
public void test() {
FunFactory.INS.registerUdf("hello", HelloOp::new);
// Now you can use the `hello` function
Expr expr = ExpretauCompiler.INS.parse("hello('world')");
RtExpr rtExpr = expr.compileIn(null);
System.out.println(rtExpr.eval(null));
}
}
Modules
| Module | Description | Documentation |
|---|---|---|
expretau_annotations |
An annotation processor to help generating some runtime code. This module is not required to using ExpreTau library. |  |
expretau_console |
An command line application to parse and evaluate expressions inputted from console. |  |
expretau_parser |
The ExpreTau parser, required to parse expression string. |  |
expretau_runtime |
The ExpreTau runtime, required to evaluate the compiled runtime object. |  |
