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comparison docs/tutorial/LangImpl1.rst @ 95:afa8332a0e37 LLVM3.8

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LLVM 3.8
author Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date Tue, 13 Oct 2015 17:48:58 +0900
parents 60c9769439b8
children 7d135dc70f03
comparison
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84:f3e34b893a5f 95:afa8332a0e37
23 23
24 It is useful to point out ahead of time that this tutorial is really 24 It is useful to point out ahead of time that this tutorial is really
25 about teaching compiler techniques and LLVM specifically, *not* about 25 about teaching compiler techniques and LLVM specifically, *not* about
26 teaching modern and sane software engineering principles. In practice, 26 teaching modern and sane software engineering principles. In practice,
27 this means that we'll take a number of shortcuts to simplify the 27 this means that we'll take a number of shortcuts to simplify the
28 exposition. For example, the code leaks memory, uses global variables 28 exposition. For example, the code uses global variables
29 all over the place, doesn't use nice design patterns like 29 all over the place, doesn't use nice design patterns like
30 `visitors <http://en.wikipedia.org/wiki/Visitor_pattern>`_, etc... but 30 `visitors <http://en.wikipedia.org/wiki/Visitor_pattern>`_, etc... but
31 it is very simple. If you dig in and use the code as a basis for future 31 it is very simple. If you dig in and use the code as a basis for future
32 projects, fixing these deficiencies shouldn't be hard. 32 projects, fixing these deficiencies shouldn't be hard.
33 33
167 // of these for known things. 167 // of these for known things.
168 enum Token { 168 enum Token {
169 tok_eof = -1, 169 tok_eof = -1,
170 170
171 // commands 171 // commands
172 tok_def = -2, tok_extern = -3, 172 tok_def = -2,
173 tok_extern = -3,
173 174
174 // primary 175 // primary
175 tok_identifier = -4, tok_number = -5, 176 tok_identifier = -4,
177 tok_number = -5,
176 }; 178 };
177 179
178 static std::string IdentifierStr; // Filled in if tok_identifier 180 static std::string IdentifierStr; // Filled in if tok_identifier
179 static double NumVal; // Filled in if tok_number 181 static double NumVal; // Filled in if tok_number
180 182
181 Each token returned by our lexer will either be one of the Token enum 183 Each token returned by our lexer will either be one of the Token enum
182 values or it will be an 'unknown' character like '+', which is returned 184 values or it will be an 'unknown' character like '+', which is returned
183 as its ASCII value. If the current token is an identifier, the 185 as its ASCII value. If the current token is an identifier, the
184 ``IdentifierStr`` global variable holds the name of the identifier. If 186 ``IdentifierStr`` global variable holds the name of the identifier. If
215 if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]* 217 if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
216 IdentifierStr = LastChar; 218 IdentifierStr = LastChar;
217 while (isalnum((LastChar = getchar()))) 219 while (isalnum((LastChar = getchar())))
218 IdentifierStr += LastChar; 220 IdentifierStr += LastChar;
219 221
220 if (IdentifierStr == "def") return tok_def; 222 if (IdentifierStr == "def")
221 if (IdentifierStr == "extern") return tok_extern; 223 return tok_def;
224 if (IdentifierStr == "extern")
225 return tok_extern;
222 return tok_identifier; 226 return tok_identifier;
223 } 227 }
224 228
225 Note that this code sets the '``IdentifierStr``' global whenever it 229 Note that this code sets the '``IdentifierStr``' global whenever it
226 lexes an identifier. Also, since language keywords are matched by the 230 lexes an identifier. Also, since language keywords are matched by the
248 252
249 .. code-block:: c++ 253 .. code-block:: c++
250 254
251 if (LastChar == '#') { 255 if (LastChar == '#') {
252 // Comment until end of line. 256 // Comment until end of line.
253 do LastChar = getchar(); 257 do
258 LastChar = getchar();
254 while (LastChar != EOF && LastChar != '\n' && LastChar != '\r'); 259 while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
255 260
256 if (LastChar != EOF) 261 if (LastChar != EOF)
257 return gettok(); 262 return gettok();
258 } 263 }