Syntax

A Eukleides source file can contain:

• Comments, i.e. all characters after a `%' to end of line.
• Simple assignments, i.e. a variable name followed by `=' and an expression.
• Multiple assignments, i.e. a space delimited sequence of variable names, followed (without `=') by a multiple assignment command (triangle assignment, polygon assignment, intersection assignment ...).
• Interactive assignments, i.e. a variable name followed by the keyword interactive with some parameters.
• Graphical commands, i.e. parameter setting commands, drawing commands or trace commands.

Variable names are case sensitive, the first character has to be a letter or an underscore character, further ones can be letters, digits, underscores or single quote characters. Variables can store various objects: number, vector, line, segment, circle, conic curve. A line of the source file can contain more than one assignment or command. (In this case they must be separated by semicolons. A semicolon at the end of the line is allowed but not necessary.)

We'll use the following notations to describe the parameters in a command:

• x, y, z : number.
• a, b : angular parameter.
• A, B, C, D, E, F, G : point.
• u, v : vector.
• l : line.
• s : segment.
• c : circle.
• cc : conic curve.
• str : string.
• f : flag.

An angular parameter is a number valued expression followed by `:' (degrees) or `<' (radians). A string is any single line text enclosed in double quotes or dollar symbols (which should be used for `"$' and `$"'). With xeukleides, in order to improve displaying of texts, dollar symbols are skipped in strings.

We'll use square brackets to indicate optional parameters.