SWI-Prolog -- function (.)/2

Documentation
- Reference manual
  - Built-in Predicates
    - Arithmetic
      - General purpose arithmetic
        
        Arithmetic Functions
        
        -/1
        
        +/1
        
        +/2
        
        -/2
        
        */2
        
        f-//2
        
        mod/2
        
        rem/2
        
        f-///2
        
        div/2
        
        rdiv/2
        
        gcd/2
        
        abs/1
        
        sign/1
        
        copysign/2
        
        max/2
        
        min/2
        
        ./2
        
        random/1
        
        random_float/0
        
        round/1
        
        integer/1
        
        float/1
        
        rational/1
        
        rationalize/1
        
        float_fractional_part/1
        
        float_integer_part/1
        
        truncate/1
        
        floor/1
        
        ceiling/1
        
        ceil/1
        
        >>/2
        
        <</2
        
        f-\//2
        
        /\/2
        
        xor/2
        
        \/1
        
        sqrt/1
        
        sin/1
        
        cos/1
        
        tan/1
        
        asin/1
        
        acos/1
        
        atan/1
        
        atan2/2
        
        atan/2
        
        sinh/1
        
        cosh/1
        
        tanh/1
        
        asinh/1
        
        acosh/1
        
        atanh/1
        
        log/1
        
        log10/1
        
        exp/1
        
        **/2
        
        ^/2
        
        powm/3
        
        lgamma/1
        
        erf/1
        
        erfc/1
        
        pi/0
        
        e/0
        
        epsilon/0
        
        inf/0
        
        nan/0
        
        cputime/0
        
        eval/1
        
        msb/1
        
        lsb/1
        
        popcount/1
        
        getbit/2
- Packages

Availability:Arithmetic function (see is/2)

A list of one element evaluates to the element. This implies "a" evaluates to the character code of the letter `a' (97) using the traditional mapping of double quoted string to a list of character codes. Arithmetic evaluation also translates a string object (see section 5.2) of one character length into the character code for that character. This implies that expression "a" also works of the Prolog flag double_quotes is set to string. The recommended way to specify the character code of the letter `a' is 0'a.