Extending expr

If you want to use C-like variable expressions that are entered by a user of your object, you can use the "guts" of Max’s expr object in your object. More...

Data Structures
struct	t_ex_ex
	ex_ex. More...
struct	t_expr
	Struct for an instance of expr. More...

Enumerations
enum	e_max_expr_types {   ET_INT, ET_FLT, ET_OP, ET_STR,   ET_TBL, ET_FUNC, ET_SYM, ET_VSYM,   ET_LP, ET_LB, ET_II, ET_FI,   ET_SI }
	Defines for ex_type. More...

Functions
void *	expr_new (long argc, t_atom *argv, t_atom *types)
	Create a new expr object. More...
short	expr_eval (t_expr *x, long argc, t_atom *argv, t_atom *result)
	Evaluate an expression in an expr object. More...

Detailed Description

If you want to use C-like variable expressions that are entered by a user of your object, you can use the "guts" of Max’s expr object in your object.

For example, the if object uses expr routines for evaluating a conditional expression, so it can decide whether to send the message after the words then or else. The following functions provide an interface to expr.

Enumeration Type Documentation

e_max_expr_types

enum e_max_expr_types

Defines for ex_type.

We treat parenthesis and brackets special to keep a pointer to their match in the content.

Enumerator
ET_INT	an int
ET_FLT	a float
ET_OP	operator
ET_STR	string
ET_TBL	a table, the content is a pointer
ET_FUNC	a function
ET_SYM	symbol ("string")
ET_VSYM	variable symbol ("$s?")
ET_LP	left parenthesis
ET_LB	left bracket
ET_II	and integer inlet
ET_FI	float inlet
ET_SI	string inlet

Function Documentation

expr_eval()

short expr_eval	(	t_expr *	x,
		long	argc,
		t_atom *	argv,
		t_atom *	result
	)

Evaluate an expression in an expr object.

Parameters

x	The expr object to evaluate.
argc	Count of arguments in argv.
argv	Array of nine t_atom values that will be substituted for variable arguments (such as $i1) in the expression. Unused arguments should be of type A_NOTHING.
result	A pre-existing t_atom that will hold the type and value of the result of evaluating the expression.

Returns

.

Remarks

Evaluates the expression in an expr object with arguments in argv and returns the type and value of the evaluated expression as a t_atom in result. result need only point to a single t_atom, but argv should contain at least argc t_atom values. If, as in the example shown above under expr_new(), there are “gaps” between arguments, they should be filled in with t_atom of type A_NOTHING.

expr_new()

void* expr_new	(	long	argc,
		t_atom *	argv,
		t_atom *	types
	)

Create a new expr object.

Parameters

argc	Count of arguments in argv.
argv	Arguments that are used to create the expr. See the example below for details.
types	A pre-existing array of nine t_atoms, that will hold the types of any variable arguments created in the expr. The types are returned in the a_type field of each t_atom. If an argument was not present, A_NOTHING is returned.

Returns

expr_new() creates an expr object from the arguments in argv and returns the type of any expr-style arguments contained in argv (i.e. $i1, etc.) in atoms in an array pointed to by types.

Remarks

types should already exist as an array of nine t_atom values, all of which will be filled in by expr_new(). If an argument was not present, it will set to type A_NOTHING. For example, suppose argv pointed to the following atoms:

$i1 (A_SYM) 
+ (A_SYM) 
$f3 (A_SYM) 
+ (A_SYM) 
3 (A_LONG) 

After calling expr_new, types would contain the following:

Index   Argument    Type        Value 
0   1 ($i1)     A_LONG      0 
1   2       A_NOTHING   0 
2   3 ($f3)     A_FLOAT     0.0 
3   4       A_NOTHING   0 
4   5       A_NOTHING   0 
5   6       A_NOTHING   0 
6   7       A_NOTHING   0 
7   8       A_NOTHING   0 
8   9       A_NOTHING   0