I'm still on my quest for a really simple language and I know now that there are none. So I'm writing one myself using ANTLR3.

I found a really great example in this answer:

Exp.g:

grammar Exp;

eval returns [double value]
    :    exp=additionExp {$value = $exp.value;}
    ;

additionExp returns [double value]
    :    m1=multiplyExp       {$value =  $m1.value;} 
         ( '+' m2=multiplyExp {$value += $m2.value;} 
         | '-' m2=multiplyExp {$value -= $m2.value;}
         )* 
    ;

multiplyExp returns [double value]
    :    a1=atomExp       {$value =  $a1.value;}
         ( '*' a2=atomExp {$value *= $a2.value;} 
         | '/' a2=atomExp {$value /= $a2.value;}
         )* 
    ;

atomExp returns [double value]
    :    n=Number                {$value = Double.parseDouble($n.text);}
    |    '(' exp=additionExp ')' {$value = $exp.value;}
    ;

Number
    :    ('0'..'9')+ ('.' ('0'..'9')+)?
    ;

WS  
    :   (' ' | '\t' | '\r'| '\n') {$channel=HIDDEN;}
    ;

Java Code:

public Double evaluate(String string, Map<String, Double> input) throws RecognitionException {
    ANTLRStringStream in = new ANTLRStringStream(string);
    ExpLexer lexer = new ExpLexer(in);
    CommonTokenStream tokens = new CommonTokenStream(lexer);
    return new ExpParser(tokens).eval();
}

Using this ANTLR grammer I can evaluate expressions like

(12+14)/2

and get 13 as a result.

Now the only thing missing for my use-case is a way to inject simple double variables into this, so that I can evaluate the following by supplying {"A": 12.0, "B":14.0} as the input map:

(A+B)/2

                    
                    

                        
                        java
                        
                        antlr
                        
                        antlr3
                        
                    

                    

                        
                        
                        
                        
                        
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