Difference between revisions of "Expressions"

Revision as of 11:18, 22 June 2007

FTM expressions are used in the following contexts

• the FTM message box ... the ftm.mess external
• FTM definitions ... the ftm.object external
• the expr class/object ... a class just like fmat or dict representing an expression

The syntax of FTM expressions allows for a maximum compatibility with messages and list as known from the Max message box.

The syntax is basically always the same appart from minor context dependent details that will be explained further below.

Single Values

The values in FTM expressions can be int, float, symbol or references to FTM object. Single values can be represended by the following items:

• a primitive value (int, float, symbol) such as '1', '2.3' and 'four'
• a named value such as '$myobj'
• an element of an object such as '$myobj[7]'
• a numbered argument such as '$1', '$2', etc.
• a tuple such as '{1 2.3 three $four}'
• an expression within parentheses such as '(1 + 2.3 / $4)'

Examples of primitive values are:

• 1 ... an int
• -2 ... an int
• 2.3 ... a float
• -4. ... a float
• 5.67e-4 ... a float
• .89 ... a float
• ten ... a symbol
• 11-12 ... a symbol (because no space!)
• -thirteen ... a symbol

Named values are defined by FTM definitions using ftm.object. The names, always representing a single value, are used in expressions with a leading dollar ('$'), as for example:

• $x
• $myobject

An element of an object can be accessed with FTM expressions using brackets ('[ ]'), as for example:

• $myvec[0]
• $mymat[0 0]
• $mydict[x]
• {0 1 2.3 $four}[$1]

Numbered arguments ('$1', '$2', '$3' etc) are especially useful in the FTM message box and can be used in the expr object. In expressions of FTM definitions with ftm.object they don't make sense and generate an error.

A tuple is an FTM object pretty much like an fmat or a dict and can show up in expressions with braces ('{ }'). The elements of a tuple are single values separated by blancs. The single value is a reference to a tuple. Since tuples are immutable objects (they don't have any methods that allow changing their size or thier values) they can be used in a similar way as lists, giving the possibilty to create tuples that contain tuples). Example of tuples are:

• {1 2.3 three $four}
• {1 2 3 {4 5 6} 7}
• {1 + 2 + 3 + 4} (7 elements!)

Lists

Single values can be concatenated to argument lists (in the message box lists or messages) with spaces like:

• 1 2.3 three
• 4 + 5.5 / six (this is a list of 5 elements)
• $myobj set 7 9.8 ten

Argument lists within parentheses will be evaluated (see below).

Parentheses

Parentheses in FTM expressions – '(' and ')' – always will (try to) evaluate the contained elements to a single value.

Inside parentheses the following sub-expressions are allowed:

• a value such as '(1)' or '($x)' or '($mydict[x])' (in which case the parentheses are useless)
• an infix expression such as '(4 + 5.5 / $six)'
• a prefix expression such '(random -90 0)' or '($myobj set 7 9.8 ten)'

Operators such as +, -, *, / are in fact only evaluated within infix expressions (and in parentheses).

... to be contiuned!