[Phase2] Update README.md

phase2/README.md

@@ -12,8 +12,21 @@
 
 ```shell
 > make splc #compile the splc compiler for SPL language
-> make test #compile the compiler and run test cases
 > make clean #clean the directory
-> make lexer #using lex.l to compile the lexer for debug 
 ```
 
+
+## Design
+- Using class `rec` as a node, there are types var, fun, arr, etc., and actions usfun, usassign, etc
+- Create initial node in lex
+- In Bison, define first, obtain a global map, link the desired elements on the nodes of all action types and then judge the action type of each node
+
+
+## Traverse Parse Tree
+- When DFS traverse the tree, the node of the action type is assigned a value of the corresponding type, which is convenient for use in nested calls later
+- In the `recs` of `rec`, for the array will store the value related to its size, the number of values represents the number of dimensions, for `Exp` expression we will store the result of the operation in the val property of rec, for return will look for a specific statement, get its val
+
+
+## Bonus
+- Tests for undefined variables are performed
+- The processing of arrays will help us to check the array overreach