Expressions

From Context Free Art

Expressions

Context Free allows expressions to be used anywhere that the compiler accepts a number, except for rule/path weights and loop counts.

Because the cfdg syntax does not separate size or skew parameters with commas, expressions like 2 - 3 are ambiguous. Does size 2 - 3 mean size -1 or does it mean size 2 -3? To resolve this issue, expressions must be put in parentheses. The only exception to this rule is that single invocations of functions do not require parentheses. So, r (360/5) and x (sin(45) + cos(60)) require parentheses, but size sqrt(1/2) does not.

The following components are allowed in an expression:

• + - : addition and subtraction
• * / : multiplication and division
• - : negation
• ^ : exponentiation
• (expression) : parentheses
• functions

Standard rules of operator ordering and precedence are supported; i.e., 2 + 3 * 4 is equivalent to 2 + (3 * 4). The list of supported functions are:

• cos(x) - cosine of x in degrees
• sin(x) - sine of x in degrees
• tan(x) - tangent of x in degrees
• acos(x) - arc-cosine of x, returned in degrees
• asin(x) - arc-sine of x, returned in degrees
• atan(x) - arc-tangent of x, returned in degrees
• atan2(y, x) - arc-tangent of y/x, returned in degrees
• log(x) - natural logarithm of x
• log10(x) - decimal logarithm of x
• exp(x) - e^x
• sqrt(x) - square root of x
• abs(x) - absolute value of x
• mod(x, y) - x modulo y

Let us know if there is a function that you would like to see added to Context Free.

startshape foo
 
path trill {
    MOVETO {x cos(234) y sin(234)}		// no parentheses required
    5* {r -144} 
        CURVETO {y 1 x1 (cos(234) + cos(324)) y1 (sin(234) + sin(324)) x2 1 y2 1}
        // parentheses required because of addition
    CLOSEPOLY {p align}
    FILL {p evenodd}
    STROKE {p buttjoin a -0.5}
}
 
rule foo {
    trill{}
}