- JavaDoc

# JEP

- Introduction
- Basic Usage
- Variables
- Data types
- Operators
- Functions
- BigDecimal
- FAQ
- Migration
- Version History

# Advanced Features

- Manipulating Expressions
- Components
- Configurable Parser
- Serialization
- Grammar

# Operators

## Built in operators

All common arithmetic operators are supported, these are provided by the StandardOperatorTable. Boolean operators are also fully supported. Relational and logical operators (>, <, >=, <=, ==, !=, !) are evaluated as Boolean types either as `Boolean.TRUE` or `Boolean.FALSE`.

An indicates that the operator can be used with the specific type of variable. Refer to the grammar for detailed information about operator precedence.

|  | Double | Complex | String | Vector
Power | ^ |  |  |  |
Boolean Not | ! |  |  |  |
Unary Plus, Unary Minus | +x, -x |  |  |  |
Dot product, cross product | ., ^^ |  |  |  |
Modulus | % |  |  |  |
Division | / |  |  |  |
Multiplication | * |  |  |  |
Addition, Subtraction | +, - |  |  | (only +) |
Less or Equal, More or Equal | <=, >= |  |  |  |
Less Than, Greater Than | <, > |  |  |  |
Not Equal, Equal | !=, == |  |  |  |
Boolean And | && |  |  |  |
Boolean Or | || |  |  |  |
Assignment | = |  |  |  |

## Adding operators

Both supplied parsers allow new operators to be added. The configurable parser makes the process quite simple but more steps are needed for using the default JavaCC parser. In both cases new operators should be added to the OperatorTable used by the Jep instance.

Before attempting to add an operator you should be familiar with adding a custom function to Jep. An instance PostfixMathCommandI (pfmc) is used to control how the operator is evaluated.

## Adding and manipulating operators for the configurable parser

To add operators to the configurable parser, they must first be added to the Operator table. Then the `jep.reinitializeComponents()` method must be called to inform the parser about the new operators. Once this is done, the parser will be able to use the new operators. It is important that the precedence and associativity of the operators has been set correctly prior to calling the method.

### Modifying an existing operator

If you just wish to change the underlying PostfixMathCommandI of an operator, for example to allow it to work with a new type of value and keeping the existing precedence and associativity and symbol, then the `setPFMC()` method of Operator can be called. The operator can be recovered from the various get methods of the OperatorTable, for instance to change the PostfixMathCommandI of the And (&&) operator use:

    jep.getOperatorTable().getAnd().setPFMC(new LazyLogical(LazyLogical.AND));

If you wish to change the symbol used to represent an operator you can use:

    jep.getOperatorTable().getAnd().setSymbol("AND");
    jep.reinitializeComponents();

Note the call to `jep.reinitializeComponents()` which is needed to inform the other components of the new symbol.

### Precedence and binding

Operators can either be binary operators (a+b), prefix unary operators (!a), suffix unary operators (i.e. like Java's x++ although no suffix operators are defined as standard) or ternary operators like Java's `a?b:c`, again not defined as standard. Static fields defining flags for each of these are defined in the Operator class, these are `Operator.BINARY`, `Operator.UNARY`, `Operator.PREFIX`, `Operator.SUFFIX`, and `Operator.NARY` for operators with 3 or more arguments.

The order in which operators are parsed depends on their precedence. For instance 1+2*3 is interpreted as 1+(2*3). The * operator has precedence over + (or in other words, it is "more tightly bound"). In Jep we use the convention that low values for precedence give a tighter binding, so the numeric value of the precedence of * is less than that of +. Precedences are always set in a relative manner as discussed below.

The parsing of operators also depends on their binding or associativity. This can either be left-associative (use `Operator.LEFT)`, like = where a=b=c is interpreted as a=(b=c), or right-associative (`Operator.RIGHT`), like - where a-b-c is interpreted as (a-b)-c. Left or right should be specified for all binary operators. A third flag `Operator.ASSOCIATIVE` is used to indicate associative operators like + this is used by print routine to determine whether to include brackets or not.

To construct an operator the constructor `public Operator(String name,PostfixMathCommandI pfmc,int flags)` is used giving the symbol used for the operator, the PostfixMathCommandI used and the sum of the flags. A second constructor `public Operator(String name,String symbol,PostfixMathCommandI pfmc,int flags)` is used when two operators share the same symbol, for example

    Operator add = new Operator("+",new Add(),
    	Operator.BINARY+Operator.LEFT+Operator.ASSOCIATIVE);
    Operator sub = new Operator("-",new Subtract(),
    	Operator.BINARY+Operator.LEFT);
    Operator mul = new Operator("*",new Multiply(),
    	Operator.BINARY+Operator.LEFT+Operator.ASSOCIATIVE);
    Operator div = new Operator("/",new Add(),
    	Operator.BINARY+Operator.LEFT);
    Operator umin = new Operator("UMinus","-",new UMinus(),
    	Operator.UNARY+Operator.RIGHT+Operator.PREFIX);
    Operator equals = new Operator("=",new Assign(),
    	Operator.BINARY+Operator.RIGHT);

There are further flags available, these specify other mathematical properties of the operators which are not currently used. For Ternary operators use the com.singularsys.jep.configurableparser.TernaryOperator.

### Adding operators to the operator table

Four methods are available for adding operators to the table:

    public Operator addOperator(Operator op);
    public Operator addOperator(Operator op, Operator existingOp);
    public Operator insertOperator(Operator op, Operator existingOp);
    public Operator appendOperator(Operator op, Operator existingOp);

The first adds an operator with no precedence set, the second adds an operator with the same precedence as an existing operator, the third and forth create a new precedence level which is either before (i.e. tighter) or after (i.e. looser) than the existing operator.

Each of these methods has a variation which allows the key code to be specified, allowing the operator to be placed in a specific place.

    OperatorTable ot = jep.getOperatorTable();
    ot.addOperator(new Operator("~",new bitComp(),Operator.UNARY+Operator.PREFIX));

To replace an existing operator, use

    ot.replaceOperator(ot.getAnd(),new Operator("AND",new And(),new Logical(0),
    	Operator.BINARY+Operator.LEFT+Operator.ASSOCIATIVE));

this will give the new operator the same precedence as the one it has replaced.

An alternative way of setting operator precedence is the setPrecedenceTable method which sets the precedence of all operators at once.

Once the operators have been added, call `jep.reinitializeComponents()` to update the Jep instance with the new operators.

The following is example output of the `OperatorTable.toString()` method.

    Operator: "^-1" UDivide unary, prefix, right binding, precedence -1.
    Operator: "LIST" variable number of arguments, infix, right binding, precedence -1.
    Operator: "[]" variable number of arguments, infix, right binding, precedence -1.
    Operator: "-" UMinus unary, prefix, right binding, precedence 0.
    Operator: "+" UPlus unary, prefix, right binding, precedence 0.
    Operator: "!" unary, prefix, right binding, precedence 0.
    Operator: "^" binary, infix, right binding, precedence 1.
    Operator: "*" binary, infix, left binding, associative, commutative, precedence 2.
    Operator: "/" binary, infix, left binding, precedence 2.
    Operator: "%" binary, infix, left binding, precedence 2.
    Operator: "." binary, infix, left binding, precedence 2.
    Operator: "^^" binary, infix, left binding, precedence 2.
    Operator: "+" binary, infix, left binding, associative, commutative, precedence 3.
    Operator: "-" binary, infix, left binding, precedence 3.
    Operator: ">" binary, infix, left binding, precedence 4, transitive.
    Operator: "<" binary, infix, left binding, precedence 4, transitive.
    Operator: "<=" binary, infix, left binding, precedence 4, reflexive, transitive.
    Operator: ">=" binary, infix, left binding, precedence 4, reflexive, transitive.
    Operator: "==" binary, infix, left binding, precedence 5, equivalence relation.
    Operator: "!=" binary, infix, left binding, precedence 5, symmetric.
    Operator: "&&" binary, infix, left binding, associative, commutative, precedence 6.
    Operator: "||" binary, infix, left binding, associative, commutative, precedence 7.
    Operator: "=" binary, infix, right binding, precedence 8.

## Adding operators using the standard parser

Adding operators to the standard parser is currently only possible by modifying the Jep source code. To add an operator to the parser, several steps are needed:

- Create a new token with the descriptive name AT, say, and a string representing the operator.
- Modify the grammar rules to include a rule for the new operator
- Add an operator as discussed above.

### Editing the standard parser grammar

The standard parser is created using the JavaCC parser/scanner generator. JavaCC reads the`JccParser.jjt` file which is written in a special language, defining the grammar. It outputs `JccParser.java` and some other Java files which implement the parser.

You should read some of the documentation on JavaCC and JJTree before attempting to modify the parser.

There is a three step process used to generate the parser.

1. JJTree is run. This reads the file`JccParser.jjt` and creates a file `JccParser.jj`. The purpose of this step is to add code needed to handle Abstract Syntax Trees which are tree structures used represent a mathematical expression. As well as creating JccParser.jj it also creates some other Java files: Node.java which represents the basic node in the parser; `ASTConstant.java` a node representing a constant value "0" or "1", `ASTVarNode.java` a node representing a variable, and `ASTFunNode.java` a node representing a function or operator.
2. JavaCC is run. This reads `JccParser.jj` and creates `JccParser.java` -- the actual code for implementing the Parser. `JccParser.java` is a very complicated file with nearly 2000 lines of code and is difficult to edit.
3. Normal Java compilation`JccParser.java` and the other classes generated by JavaCC.

This process is automatically carried out when the project is built using the ANT `build.xml` file. It is not sufficient to simply recompile all the Java files.

Only the `JccParser.jjt` file should be modified, `JccParser.jj` and`JccParser.java` should not be modified as they will be overwritten during the build process. Furthermore `ASTConstant.java, ASTFunNode.java, ASTStart.java, ASTVarNode.java, JavaCharStream.java, JJTParserState.java, Node.java, SimpleNode.java, ParseException.java, JccParserConstants.java, JccParserTokenManager.java, JccParseTreeConstants.java, Token.java`, and `TokenMgrError.java` should not normally be modified as these are also automatically generated.

## Additional operator sets

The com.singularsys.jep.misc package contains two operators tables which contain additional operators: com.singularsys.jep.misc.bitwise.BitwiseOperatorTable and com.singularsys.jep.misc.javaops.JavaOperatorTable.

| Standard symbol | Bitwise OperatorTable | Java OperatorTable | Arguments
--- | --- | --- | --- | ---
Bitwise and | & |  |  | Integer
Bitwise or | | |  |  | Integer
Bitwise xor | ^* |  |  | Integer
Bitwise complement | ~ |  |  | Integer
Leftshift | << |  |  | Integer
Signed rightshift | >> |  |  | Integer
Unsigned rightshift | >>> |  |  | Integer
Pre-increment/decrement | ++x, --x |  |  | Double variable
Post-increment/decrement | x++, x-- |  |  | Double variable
Conditional | ?: |  |  | Double
Assignment | +=, -=, *=, /=, %= |  |  | Double
Bitwise assignment | &=, |=, ^=, <<=, >>=, >>>= |  |  | Integer

Notes: the bitwise xor operator has the same symbol as normally used for power. The constructors for the tables allow the symbol to be specified, the defaults are power (**) and xor (^). Bitwise operators and assignment convert their arguments to Integer and return arguments as `java.lang.Integer`. Pre and post increment/decrement operators require a variable as argument who's value will be treated as a Double.