Rudiments of a recursive descent parser.
Cat's Eye Technologies
12 years ago
| 0 | 0 | #!/usr/bin/env python |
| 1 | 1 | |
| 2 | """An attempt to implement Xoomonk in Python. Embryonic, as of this writing; | |
| 3 | only includes some runtime support, no parser. | |
| 2 | """An attempt to implement Xoomonk in Python. | |
| 4 | 3 | |
| 5 | 4 | """ |
| 5 | ||
| 6 | class Scanner(object): | |
| 7 | def __init__(self, text): | |
| 8 | self.text = text | |
| 9 | self.scan() | |
| 10 | ||
| 11 | def scan(self): | |
| 12 | pass | |
| 13 | ||
| 14 | def expect(self, token): | |
| 15 | if self.token == token: | |
| 16 | self.scan() | |
| 17 | else: | |
| 18 | raise SyntaxError("expected %s" % token) | |
| 19 | ||
| 20 | def on(self, token): | |
| 21 | return self.token == token | |
| 22 | ||
| 23 | def consume(self, token): | |
| 24 | if self.token == token: | |
| 25 | self.scan() | |
| 26 | return True | |
| 27 | else: | |
| 28 | return False | |
| 29 | ||
| 30 | ||
| 31 | # Parser | |
| 32 | ||
| 33 | class Parser(object): | |
| 34 | def program(self): | |
| 35 | while not self.scanner.at_end(): | |
| 36 | self.stmt() | |
| 37 | ||
| 38 | def stmt(self): | |
| 39 | if self.scanner.on("print"): | |
| 40 | self.print_stmt() | |
| 41 | else: | |
| 42 | self.assign() | |
| 43 | ||
| 44 | def assign(self): | |
| 45 | self.ref() | |
| 46 | self.scanner.expect(":=") | |
| 47 | self.expr() | |
| 48 | ||
| 49 | def print_stmt(self): | |
| 50 | self.scanner.expect("print") | |
| 51 | if self.scanner.consume("string"): | |
| 52 | st = self.scanner.token | |
| 53 | self.scanner.scan() | |
| 54 | elif self.scanner.consume("char"): | |
| 55 | self.expr() | |
| 56 | else: | |
| 57 | self.expr() | |
| 58 | if self.scanner.consume(";"): | |
| 59 | # mark as no nl | |
| 60 | pass | |
| 61 | ||
| 62 | def expr(self): | |
| 63 | v = None | |
| 64 | if self.scanner.on("{"): | |
| 65 | v = self.block() | |
| 66 | elif self.scanner.on_pattern(r'\d+'): | |
| 67 | v = int(self.token) | |
| 68 | else: | |
| 69 | v = self.ref() | |
| 70 | if self.scanner.consume("*"): | |
| 71 | # v = copy(v) | |
| 72 | pass | |
| 73 | return v | |
| 74 | ||
| 75 | def block(self): | |
| 76 | self.scanner.expect("{") | |
| 77 | while not self.scanner.on("}"): | |
| 78 | self.stmt() | |
| 79 | self.scanner.expect("}") | |
| 80 | ||
| 81 | def ref(self): | |
| 82 | self.name() | |
| 83 | while self.scanner.consume("."): | |
| 84 | self.name() | |
| 85 | ||
| 86 | def name(self): | |
| 87 | if self.scanner.consume("^"): | |
| 88 | return "^" | |
| 89 | elif self.scanner.consume("$"): | |
| 90 | return self.scanner.token | |
| 91 | else: | |
| 92 | return self.scanner.token | |
| 93 | ||
| 6 | 94 | |
| 7 | 95 | # Runtime support for Xoomonk. |
| 8 | 96 |