5.2 Conditional Statements

Syntax for conditional statement is:

     if assertion block { { elseif  assertion block } ... else block } end

Example:

     if x < 0
       print "x is negative."
     elseif x > 0
       print "x is positive."
     else
       print "x is null."
     end

Using the stop command within a conditional statement allows to abort the execution of a script when some condition is met.

Boolean operators

not a

Negation of assertion a.

a and b

Disjunction of assertions a and b.

a or b

Conjunction of assertions a and b.

Boolean constants

true

false

Comparison operators

a == b

Checks whether objects a and b are equal, i.e. have the same internal representation. Objects may be numbers, strings, points, vectors, sets, lines, circles or conics.

a != b

Negation of the former.

x < y

x <= y

x > y

x >= y

Comparison of numbers x and y.

Set assertions

A in s

Checks whether point A belongs to set s.

empty(s)

Checks for emptiness of set s.

Geometric assertions

A on s

Checks whether point A is on object s, where s may be a set (considered as an open path), a line, a circle or a conic.

collinear(A, B, C)

Checks whether points A, B and C are collinear.

collinear(u, v)

Checks whether vectors u and v are collinear, i.e. have same or opposite directions.

parallel(l, l')

perpendicular(l, l')

Direction comparison of lines l and l'.

ellipse(c)

hyperbola(c)

parabola(c)

Type checking of conic c.

isosceles(A, B, C)

equilateral(A, B, C)

right(A, B, C)

Type checking of triangle ABC.

parallelogram(A, B, C, D)

rectangle(A, B, C, D)

square(A, B, C, D)

Type checking of quadrilateral ABCD.

Output format flags

eps

True with eukleides.

pstricks

True with euktopst.

display

True within GUI.

Ternary operator

assertion ? x | y

Number x if assertion is true, number y otherwise.