ChucK : Language Specification > Operators

version: 1.3.x.x (chimera)

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Operators & Operations

Operations on data are achieved through operators. This sections defines how operators behave on various datatypes. You may have seen many of the operators in other programming languages (C/Java). Some others are native to ChucK. We start with the family of ChucK operators.

View sample code for operators & operations

=> (the ChucK operator)

The ChucK operator (=>) is a massively overloaded operator that, depending on the types involved, performs various actions. It denotes action, can be chained, and imposes and clarifies order (always goes from left to right). The ChucK operator is the means by which work is done in ChucK. Furthermore, the ChucK operator is not a single operator, but a family of operators.

=> (foundational ChucK operator)

We start with the standard, plain-vanilla ChucK operator (=>). It is left-associative (all ChucK operators are), which allows us to specify any ordered flow of data/tasks/modules (such as unit generator connection) from left-to-right, as in written (English) text. What => does depends on the context. It always depends on the type of the entity on the left (the chucker) and the one on the right (the chuckee), and it sometimes also depends on the nature of the entity (such as whether it is a variable or not).

Some examples:

    // a unit generator patch - the signal flow is apparent
    // (in this case, => connects two unit generators)
    SinOsc b => Gain g => BiQuad f => dac;
    // add 4 to foo, chuck result to new 'int' variable 'bar'
    // (in this case, => assigns a value to a variable (int)
    4 + foo => int bar;
    // chuck values to a function == function call
    // (same as Math.rand2f( 30, 1000))
    ( 30, 1000 ) => Math.rand2f;

There are many other well-defined uses of the ChucK operator, depending on the context.

@=> (explicit assignment ChucK operator)

In ChucK, there is no stardard assignment operator (=), found in many other programming languages. Assignment is carried out using ChucK operators. In the previous examples, we have used => for assignment:

    // assign 4 to variable foo
    4 => int foo;

    // assign 1.5 to variable bar
    1.5 => float bar;

    // assign duration of 100 millisecond to duh
    100::ms => dur duh;

    // assign the time "5 second from now" to later
    5::second + now => time later;

The @=> explicit assignment ChucK operator behaves exactly the same for the above types (int, float, dur, time). However, the difference is that @=> can also be used for reference assignments of objects (see objects and classes) whereas => only does assignment on primitive types (int, float, dur, time). The behavior of => on objects is completely context-dependent.

    // using @=> is same as => for primitive types
    4 @=> int foo;

    // assign 1.5 to variable bar
    1.5 @=> float bar;

    // (only @=> can perform reference assignment on objects)

    // reference assign moe to larry
    // (such that both moe and larry reference the same object)
    Object moe @=> Object @ larry;

    // array initialization
    [ 1, 2 ] @=> int ar[];

    // using new
    new Object @=> moe;

In its own screwed-up way, this is kind of nice because there is no confusion between assignment (@=> or =>) and equality (==). In fact the following is not a valid ChucK statement:

    // not a valid ChucK statement!
    int foo = 4;

+=>  -=>  *=>  /=>  etc. (arithmetic ChucK operators)

These operators are used with variables (using 'int' and 'float') to perform one operation with assignment.

    // add 4 to foo and assign result to foo
    foo + 4 => foo;

    // add 4 to foo and assign result to foo
    4 +=> foo;

    // subtract 10 from foo and assign result to foo
    // remember this is (foo-10), not (10-foo)
    10 -=> foo;

    // 2 times foo assign result to foo
    2 *=> foo;

    // divide 4 into foo and assign result to foo
    // again remember this is (foo/4), not (4/foo)
    4 /=> foo;

It is important to note the relationship between the value and variable when using -=> and /=>, since these operations are not commutative.

    // mod foo by T and assign result to foo
    T %=> foo;

    // bitwise AND 0xff and bar and assign result to bar
    0xff &=> bar;

    // bitwise OR 0xff and bar and assign result to bar
    0xff |=> bar;

That's probably enough operator abuse for now...

+  -  *  /  (arithmetic)

Can you add, subtract, multiply and divide? So can ChucK!

    // divide (and assign)
    16 / 4 => int four;

    // multiply
    2 * 2 => four;

    // add
    3 + 1 => four;

    // subtract
    93 - 89 => four;

cast

ChucK implicitly casts int values to float when float is expected, but not the other around. The latter could result in a loss of information and requires an explicit cast.

    // adding float and int produces a float
    9.1 + 2 => float result;

    // however, going from float to int requires cast
    4.8 $ int => int foo;  // foo == 4

    // this function expects two floats
    Math.rand2f( 30.0, 1000.0 );

    // this is ok because of implicit cast
    Math.rand2f( 30, 1000 );

% (modulo)

The modulo operator % computes the remainder after integer, floating point, duration, and time/duration division.

    // 7 mod 4 (should yield 3)
    7 % 4 => int result;

    // 7.3 mod 3.2 floating point mod (should yield .9)
    7.3 % 3.2 => float resultf;

    // duration mod
    5::second % 2::second => dur foo;

    // time/duration mod
    now % 5::second => dur bar;

the latter (time/duration mod) is one of many ways to dynamically synchronize timing in shreds. the examples otf_01.ck through otf_07.ck (see under examples) make use of this to on-the-fly synchronize its various parts, no matter when each shred is added to the virtual machine:

    // define period (agreed upon by several shreds)
    .5::second => dur T;

    // compute the remainder of the current period ...
    // and advance time by that amount
    T - (now % T) => now;

    // when we reach this point, we are synchronized to T period boundary
    
    // the rest of the code
    // ...

This is one of many ways to compute and reason about time in ChucK. The appropriate solution(s) in each case depends on the intended functionality. Have fun!

&&  ||  ==  !=  >  >=  <  <=  (logic)

Logical operators - each of these need two operands. The result is an integer value of 0 or 1.

  • && : and
  • || : or
  • == : equals
  • != : does not equal
  • > : greater than
  • >= : greater than or equal to
  • < : less than
  • <= : less than or equal to
    // test some universal truths
    if( 1 <= 4 && true )
        <<<"horray">>>;

>>  <<  &  |  ^  (bitwise)

These are used on int values at the bit level, often for bit masking.

  • >> : shift bits right ( 8 >> 1 = 4 )
  • << : shift bits left ( 8 << 1 = 16 )
  • & : bitwise AND
  • | : bitwise OR
  • ^ : bitwise XOR

++  --  (inc / dec)

Values may be incremented or decremented by appending the ++ or -- operators.

4 => int foo;
foo++;
foo--;

! + - new (unary)

These operators come before one operand.

    // logical invert
    if( !true == false )
        <<<"yes">>>;

    // negative
    -1 => int foo;

    // instantiate object
    new object @=> object @ bar;
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