BRE Language Features
- Fully typed language (integer, boolean, float, string).
- Supports arrays and sets.
- Grouping functions (MIN, MAX, SUM, COUNT)
- Has functions, constants and special group definitions.
- Can call external functions.
- Has the For All, For Some, Exists logical predicates
- Generates portable byte-codes.
- Local Variables, Recursion supported.
- Complex String matching capabilities.
BRE Language Samples
The BRE language consists of a series of rule & function definitions. The language is parsed using yacc and compiled into a byte-code representation. The rules are evaluated by executing the bytes codes and checking for a TRUE/FALSE return value. Here are some actual rules from our rule file:
--
-- Returns TRUE if 'str' consists of all letters.
--
function is_alpha(str) is
str: string;
for all ch in str
ch in "abcdefghijklmnopqrstuvwxyz"
or
ch in "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
-- The sum of the line items tax fields must equal
-- the header's tax field.
rule cc1 is
sum(ORDER_LINE_ITEMS.TAX-AMT) = ORDER_HEADER.TAX-AMT
rule 703 using ORDER_LINE_ITEMS is
if ENTRY-KEY in {" ", "M", "#"} and PURCH-AGREE <> null
then BT <> null
-- DLR-LINE-TOTAL
-- Changed by Peter Weck to allow for both OP-ORDER-PRICE and
-- DLR-LINE-TOTAL to be zero
rule 857 using ORDER_LINE_ITEMS is
if ENTRY-KEY in {" ","M","#"} and ORDER_HEADER.TRADE-IC = "T" then
(OP-ORDER-PRICE > 0.0 and DLR-LINE-TOTAL >= 0.0)
or (OP-ORDER-PRICE < 0.0 and DLR-LINE-TOTAL <= 0.0)
or (OP-ORDER-PRICE = 0.0 and DLR-LINE-TOTAL = 0.0)
rule cc19 is
if (for all li in ORDER_LINE_ITEMS
li.ENTRY-KEY <> " " or li.HP-GSA = " ") then
ORDER_HEADER.COMMERCE-CODE <> "4"
fail with: li.ENTRY-KEY, ORDER_HEADER.COMMERCE-CODE
Byte Code Sample
The following is a disassembly of the byte-codes that were generated for the is_alpha() function. In software a stack based machine is implemented to execute these instructions. This sample occupies only 160 bytes of storage.
00000: ENTRY S0=1 ; ----- function is_alpha ----- 00004: GETFP S0=-2 00008: PUSH_I L0=0 00016: GETSP S0=-2 00020: COUNT_S 00021: GETSP S0=-2 00024: SUB_I 00025: BRANCH_ZERO B0=1 L0=152 00032: GETSP S0=-2 00036: GETSP S0=-2 00040: FETCH_CHAR 00041: ASSIGN B0=1 S0=1 00046: INCSP S0=-1 00050: GETFP S0=1 00054: PUSH_S S0=26 STR0="abcdefghijklmnopqrstuvwxyz" 00085: IN_SS 00086: BRANCH_TRUE B0=0 L0=128 00092: POP 00093: GETFP S0=1 00096: PUSH_S S0=26 STR0="ABCDEFGHIJKLMNOPQRSTUVWXYZ" 00127: IN_SS 00128: BRANCH_TRUE B0=1 L0=16 00136: POP 00137: POP 00138: PUSH_I L0=0 00144: BRANCH L0=160 00152: POP 00153: POP 00154: PUSH_I L0=1 00160: RETURN S0=1