104 lines
2.9 KiB
Java
104 lines
2.9 KiB
Java
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import ASTTree;
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/* *
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* descent recursive parser, convert regex to nfa-tree.
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* the BNF of the regex is from:
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* https://www2.cs.sfu.ca/~cameron/Teaching/384/99-3/regexp-plg.html
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*
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*/
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public class Parser{
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private String characterList;
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private int index;
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private int nextIndex;
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public Parser(){
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this.characterList = null;
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this.index = 0;
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this.nextIndex = 1;
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}
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private moveForward(){
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this.index += 1;
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if (this.index < this.characterList.length() - 1){
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this.nextIndex += 1;
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}
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else{
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this.nextIndex = null;
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}
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}
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private parse(String regexStr){
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return this.expr();
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}
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}
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/*
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"""expr = term,{“+",term}"""
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def expr():
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global token_list, current_token_index
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result = term() # go to lower grammar rule
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"""using loops to save the recursivily-defined grammar.
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If the next token can't be gotten, don't enter the loop"""
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while next_token_index != None and token_list[next_token_index] == "+":
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# if the result is a list, set the left term (result) as the left item(sub-tree).
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left = result
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move_forward()
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middle = token_list[current_token_index]
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move_forward()
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right = term()
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"""arrange the syntax tree (in S-exp like form)"""
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result = [middle, left, right]
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return result
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"""term = factor,{“∗",factor}"""
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def term():
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global token_list, current_token_index
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result = factor()
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while next_token_index != None and token_list[next_token_index] == "*":
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left = result
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move_forward()
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middle = token_list[current_token_index]
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move_forward()
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right = term()
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"""arrange the syntax tree (in S-exp like form)"""
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result = [middle, left, right]
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return result
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'''factor = “0"|“1"|“2"|“3"|“4"|“5"|“6"|“7"|“8"|“9"'''
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def factor():
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global token_list, current_token_index
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item = int(token_list[current_token_index])
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# if it matches the pattern, return the number in integer type, or raise a error.
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if item in range(0,10): # pattern = 0, 1, 2, ..., 9
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return item
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else:
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raise Exception("Except integer from 0 to 9, given %d" % item)
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/*
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<RE> ::= <union> | <simple-RE>
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<union> ::= <RE> "|" <simple-RE>
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<simple-RE> ::= <concatenation> | <basic-RE>
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<concatenation> ::= <simple-RE> <basic-RE>
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<basic-RE> ::= <star> | <plus> | <elementary-RE>
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<star> ::= <elementary-RE> "*"
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<plus> ::= <elementary-RE> "+"
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<elementary-RE> ::= <group> | <any> | <eos> | <char> | <set>
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<group> ::= "(" <RE> ")"
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<any> ::= "."
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<eos> ::= "$"
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<char> ::= any non metacharacter | "\" metacharacter
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<set> ::= <positive-set> | <negative-set>
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<positive-set> ::= "[" <set-items> "]"
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<negative-set> ::= "[^" <set-items> "]"
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<set-items> ::= <set-item> | <set-item> <set-items>
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<set-items> ::= <range> | <char>
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<range> ::= <char> "-" <char> */
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