Enabling & Disabling Features¶
The parser can be configured via its settings instance to either allow or disallow certain features that are available within the MathExpr grammar. The features fall into one of the following six categories:
- Base Functions
- Control Flow Structures
- Logical Operators
- Arithmetic Operators
- Inequality Operators
- Assignment Operators
Base Functions¶
The list of available base functions is as follows:
abs, acos, acosh, asin, asinh, atan, atanh, atan2, avg, ceil, clamp, cos, cosh, cot, csc, equal, erf, erfc, exp, expm1, floor, frac, hypot, iclamp, like, log, log10, log2, logn, log1p, mand, max, min, mod, mor, mul, ncdf, pow, root, round, roundn, sec, sgn, sin, sinc, sinh, sqrt, sum, swap, tan, tanh, trunc, not_equal, inrange, deg2grad, deg2rad, rad2deg, grad2deg
The above mentioned base functions can be either enabled or disabled 'all' at once, as is demonstrated below:
parser_t parser;
expression_t expression;
parser.settings().disable_all_base_functions();
parser
.compile("2 * abs(2 - 3)",expression); // compilation failure
parser.settings().enable_all_base_functions();
parser
.compile("2 * abs(2 - 3)",expression); // compilation success
One can also enable or disable specific base functions. The following example demonstrates the disabling of the trigonometric functions 'sin' and 'cos':
parser_t parser;
expression_t expression;
parser.settings()
.disable_base_function(settings_t::e_bf_sin)
.disable_base_function(settings_t::e_bf_cos);
parser
.compile("(sin(x) / cos(x)) == tan(x)",expression); // failure
parser.settings()
.enable_base_function(settings_t::e_bf_sin)
.enable_base_function(settings_t::e_bf_cos);
parser
.compile("(sin(x) / cos(x)) == tan(x)",expression); // success
Control Flow Structures¶
The list of available control flow structures is as follows:
- If or If-Else
- Switch statement
- For Loop
- While Loop
- Repeat Loop
The above mentioned control flow structures can be either enabled or disabled 'all' at once, as is demonstrated below:
parser_t parser;
expression_t expression;
const std::string program =
" var x := 0; "
" for (var i := 0; i < 10; i += 1) "
" { "
" x += i; "
" } ";
parser.settings().disable_all_control_structures();
parser
.compile(program,expression); // compilation failure
parser.settings().enable_all_control_structures();
parser
.compile(program,expression); // compilation success
One can also enable or disable specific control flow structures. The following example demonstrates the disabling of the for-loop control flow structure:
parser_t parser;
expression_t expression;
const std::string program =
" var x := 0; "
" for (var i := 0; i < 10; i += 1) "
" { "
" x += i; "
" } ";
parser.settings()
.disable_control_structure(settings_t::e_ctrl_for_loop);
parser
.compile(program,expression); // failure
parser.settings()
.enable_control_structure(settings_t::e_ctrl_for_loop);
parser
.compile(program,expression); // success
Logical Operators¶
The list of available logical operators is as follows:
and, nand, nor, not, or, xnor, xor, &, |
The above mentioned logical operators can be either enabled or disabled 'all' at once, as is demonstrated below:
parser_t parser;
expression_t expression;
parser.settings().disable_all_logic_ops();
parser
.compile("1 or not(0 and 1)",expression); // compilation failure
parser.settings().enable_all_logic_ops();
parser
.compile("1 or not(0 and 1)",expression); // compilation success
One can also enable or disable specific logical operators. The following example demonstrates the disabling of the 'and' logical operator:
parser_t parser;
expression_t expression;
parser.settings()
.disable_logic_operation(settings_t::e_logic_and);
parser
.compile("1 or not(0 and 1)",expression); // failure
parser.settings()
.enable_logic_operation(settings_t::e_logic_and);
parser
.compile("1 or not(0 and 1)",expression); // success
Arithmetic Operators¶
The list of available arithmetic operators is as follows:
The above mentioned arithmetic operators can be either enabled or disabled 'all' at once, as is demonstrated below:
parser_t parser;
expression_t expression;
parser.settings().disable_all_arithmetic_ops();
parser
.compile("1 + 2 / 3",expression); // compilation failure
parser.settings().enable_all_arithmetic_ops();
parser
.compile("1 + 2 / 3",expression); // compilation success
One can also enable or disable specific arithmetic operators. The following example demonstrates the disabling of the addition '+' arithmetic operator:
parser_t parser;
expression_t expression;
parser.settings()
.disable_arithmetic_operation(settings_t::e_arith_add);
parser
.compile("1 + 2 / 3",expression); // failure
parser.settings()
.enable_arithmetic_operation(settings_t::e_arith_add);
parser
.compile("1 + 2 / 3",expression); // success
Inequality Operators¶
The list of available inequality operators is as follows:
<, <=, >, >=, ==, =, != <>
The above mentioned inequality operators can be either enabled or disabled 'all' at once, as is demonstrated below:
parser_t parser;
expression_t expression;
parser.settings().disable_all_inequality_ops();
parser
.compile("1 < 3",expression); // compilation failure
parser.settings().enable_all_inequality_ops();
parser
.compile("1 < 3",expression); // compilation success
One can also enable or disable specific inequality operators. The following example demonstrates the disabling of the less-than '<' inequality operator:
parser_t parser;
expression_t expression;
parser.settings()
.disable_inequality_operation(settings_t::e_ineq_lt);
parser
.compile("1 < 3",expression); // failure
parser.settings()
.enable_inequality_operation(settings_t::e_ineq_lt);
parser
.compile("1 < 3",expression); // success
Assignment Operators¶
The list of available assignment operators is as follows:
:=, +=, -=, *=, /=, %=
The above mentioned assignment operators can be either enabled or disabled 'all' at once, as is demonstrated below:
T x = T(0);
parser_t parser;
expression_t expression;
symbol_table_t symbol_table;
symbol_table.add_variable("x",x);
expression.register_symbol_table(symbol_table);
parser.settings().disable_all_assignment_ops();
parser
.compile("x := 3",expression); // compilation failure
parser.settings().enable_all_assignment_ops();
parser
.compile("x := 3",expression); // compilation success
One can also enable or disable specific assignment operators. The following example demonstrates the disabling of the '+=' addition assignment operator:
T x = T(0);
parser_t parser;
expression_t expression;
symbol_table_t symbol_table;
symbol_table.add_variable("x",x);
expression.register_symbol_table(symbol_table);
parser.settings()
.disable_assignment_operation(settings_t::e_assign_addass);
parser
.compile("x += 3",expression); // failure
parser.settings()
.enable_assignment_operation(settings_t::e_assign_addass);
parser
.compile("x += 3",expression); // success
Note 30. In the event of a base function being disabled, one can redefine the base function using the standard custom function definition process. In the following example the 'sin' function is disabled then redefined as a function taking degree input.
template <typename T>
struct sine_deg final : public math_expr::ifunction<T>
{
sine_deg() : math_expr::ifunction<T>(1) {}
inline T operator()(const T& v) override
{
const T pi = math_expr::details::numeric::constant::pi;
return std::sin((v * T(pi)) / T(180));
}
};
...
typedef math_expr::symbol_table<T> symbol_table_t;
typedef math_expr::expression<T> expression_t;
typedef math_expr::parser<T> parser_t;
typedef typename parser_t::settings_store settings_t;
sine_deg<T> sine;
symbol_table.add_reserved_function("sin",sine);
expression_t expression;
expression.register_symbol_table(symbol_table);
parser_t parser;
parser.settings()
.disable_base_function(settings_t::e_bf_sin);
parser.compile("1 + sin(30)",expression);
In the example above, the custom 'sin' function is registered with the symbol_table using the method 'add_reserved_function'. This is done so as to bypass the checks for reserved words that are carried out on the provided symbol names when calling the standard 'add_function' method. Normally if a user specified symbol name conflicts with any of the MathExpr reserved words, the add_function call will fail.