Expression
This component implements the functionality to parse a simple expression. The expression supports only variables, constants, and functions.
The syntax is as follows:
abc -- This is a variable
"abc" -- This is a string constant
'abc' -- This is also a string constant
1 -- Integer
1.2 -- Float
0xa -- Hexadecimal integer
0311 -- Octal integer
concat(abc, bcd) -- This is a function with two parameters, both are variables
concat(abc, "bcd") -- This is a function with two parameters, one is a variable and the other is a constant
concat(1, "bcd") -- Both parameters are constants
concat("abc", concat(bcd, "efg")) -- This example demonstrates nested function calls
concat("abc", concat(bcd, "efg")) aaa concat("bcd", concat(efg, "hij")) -- This example demonstrates running multiple expressions
-- if else
if a then
var1
else
func2()
fi
if a then
func1()
if b then
fi
else
if c then
else
fi
fi
-- loop
loop condition do
aaa
func(func2())
if a then
bbb
else
ccc
fi
end
Header file
#include "mln_expr.h"
Module
expr
Functions
mln_expr_val_new
mln_expr_val_t *mln_expr_val_new(mln_expr_typ_t type, void *data, mln_expr_udata_free free);
typedef void (*mln_expr_udata_free)(void *);
typedef enum {
mln_expr_type_null = 0,
mln_expr_type_bool,
mln_expr_type_int,
mln_expr_type_real,
mln_expr_type_string,
mln_expr_type_udata,
} mln_expr_typ_t;
typedef struct {
mln_expr_typ_t type;
union {
mln_u8_t b;
mln_s64_t i;
double r;
mln_string_t *s;
void *u;
} data;
mln_expr_udata_free free;
} mln_expr_val_t;
Description: Create an expression value object. mln_expr_typ_t is the type of the expression, and mln_expr_val_t is the structure of the value object. Depending on the first parameter, the second parameter of the function mln_expr_val_new can have the following types:
mln_u8_t *mln_s64_t *double *mln_string_t *Strings will be referenced using themln_string_refwithin the function.void *User-defined data. It can be freed by the free function indicated by the third parameter of this function.
Return values:
- On success: Pointer to
mln_expr_val_t - On failure:
NULL
mln_expr_val_free
void mln_expr_val_free(mln_expr_val_t *ev);
Description: Free an expression value object. If the value is of type string and the free callback is also set, then the string will be freed using free; otherwise, mln_string_free will be used for freeing.
Return value: None
mln_expr_val_copy
void mln_expr_val_copy(mln_expr_val_t *dest, mln_expr_val_t *src);
Description: duplicate an expression value object. Duplicate the content of src to dest. If the type is a string, the function mln_string_ref will be used to reference the string. If it is of type udata, simply copy the data pointer and set src's free to NULL, ensuring that the user-defined data is not freed when src is released.
Return value: None
mln_expr_val_dup
void mln_expr_val_dup(mln_expr_val_t *val);
Description: Copy an expression value object. Similar to mln_expr_val_copy, but allocates a completely new block of memory.
Return values:
- On success: Pointer to
mln_expr_val_t - On failure:
NULL
mln_expr_run
mln_expr_val_t *mln_expr_run(mln_string_t *exp, mln_expr_cb_t cb, void *data);
typedef mln_expr_val_t *(*mln_expr_cb_t)(mln_string_t *name, int is_func, mln_array_t *args, void *data);
Description: Run the expression exp. Variables and functions (along with their arguments) in the expression, as well as user-defined data data, will be passed to the callback function cb for evaluation. Developers can customize the values of these functions and variables as needed.
Return values:
- On success: Pointer to
mln_expr_val_t, containing the result of the evaluation - On failure:
NULL
mln_expr_run_file
mln_expr_val_t *mln_expr_run_file(mln_string_t *path, mln_expr_cb_t cb, void *data);
typedef mln_expr_val_t *(*mln_expr_cb_t)(mln_string_t *name, int is_func, mln_array_t *args, void *data);
Description: Run the expression specified in the file identified by path. Variables and functions (along with their arguments) in the expression, as well as user-defined data data, will be passed to the callback function cb for evaluation. Developers can customize the values of these functions and variables as needed.
Return values:
- On success: Pointer to
mln_expr_val_t, containing the result of the evaluation - On failure:
NULL
Example
#include "mln_expr.h"
#include "mln_log.h"
#include <stdio.h>
static mln_expr_val_t *var_expr_handler(mln_string_t *name, int is_func, mln_array_t *args, void *data)
{
mln_string_t *s;
mln_expr_val_t *ret;
printf("%p %p %p\n", name, args, data);
if (is_func)
mln_log(none, "%S %d %U %X\n", name, is_func, args->nelts, data);
else
mln_log(none, "%S %d %X\n", name, is_func, data);
if ((s = mln_string_dup(name)) == NULL) return NULL;
ret = mln_expr_val_new(mln_expr_type_string, s, NULL);
mln_string_free(s);
return ret;
}
static mln_expr_val_t *func_expr_handler(mln_string_t *name, int is_func, mln_array_t *args, void *data)
{
mln_expr_val_t *v, *p;
int i;
mln_string_t *s1 = NULL, *s2, *s3;
if (!is_func)
return mln_expr_val_new(mln_expr_type_string, name, NULL);
for (i = 0, v = p = mln_array_elts(args); i < mln_array_nelts(args); v = p + (++i)) {
if (s1 == NULL) {
s1 = mln_string_ref(v->data.s);
continue;
}
s2 = v->data.s;
s3 = mln_string_strcat(s1, s2);
mln_string_free(s1);
s1 = s3;
}
v = mln_expr_val_new(mln_expr_type_string, s1, NULL);
mln_string_free(s1);
return v;
}
int main(void)
{
mln_string_t var_exp = mln_string("aaa bbb");
mln_string_t func_exp = mln_string("concat('abc', concat(aaa, 'bbb')) ccc concat('eee', concat(bbb, 'fff'))");
mln_expr_val_t *v;
v = mln_expr_run(&var_exp, var_expr_handler, NULL);
if (v == NULL) {
mln_log(error, "run failed\n");
return -1;
}
mln_log(debug, "%d %S\n", v->type, v->data.s);
mln_expr_val_free(v);
v = mln_expr_run(&func_exp, func_expr_handler, NULL);
if (v == NULL) {
mln_log(error, "run failed\n");
return -1;
}
mln_log(debug, "%d %S\n", v->type, v->data.s);
mln_expr_val_free(v);
return 0;
}
Execution result:
0x4bbb720 (nil) (nil)
aaa 0 0
0x4bbb830 (nil) (nil)
bbb 0 0
03/19/2024 00:17:17 UTC DEBUG: a.c:main:59: PID:2317789 4 bbb
03/19/2024 00:17:17 UTC DEBUG: a.c:main:67: PID:2317789 4 eeebbbfff