Syntax and parser generators I
Lecture 3
Table of Contents
Review
Questions about the last class?
Quiz
What is the difference between a compiler and an interpreter? Also, give one example of each.
Quiz Discussion
Review: Phases of a compiler
- Syntax analysis
- Type checking
- Code generation
Syntax analysis
- Turn text into a parse tree
- Identifies words (tokens, lexemes) in the language
- Grammar gives a name to each language construct
- Map is not the territory
- Nothing in the text of a sentence says "this is a sentence"
- We know because of the word order
- Grammar defines all the legal word orders
- Map is not the territory
Type checking
- Verifies that symbols are used correctly
- numbers added to numbers, not function
- Will be more specific in the next phase
Code generation
- Intermediate code (for us this is C)
- Machine code (this is the C to ASM compiler, which has its own compiler phases)
Review: Grammars
Using ANTLR
- Setting up the environment
Example: calculator
- Work out the grammar in class by hand
- Order of operations
- Test it with some examples
Defining Calc.g4
- Overview of ANTLR grammars
- Lexer vs. parser
Generating the parser
# add antlr to your classpath; your path to the runtime may vary export CLASSPATH=/usr/share/java/antlr4-runtime.jar:$CLASSPATH # this generates the parser antlr4 Calc.g4 # this compiles the parser javac *.java # use -gui to display a parse tree graphically echo "1*2+3" | /usr/share/antlr4/grun Calc expr -gui # demonstrate order of operations echo "1+2*3" | /usr/share/antlr4/grun Calc expr -gui # use -tree to display a parse tree textually echo "1*2+3" | /usr/share/antlr4/grun Calc expr -tree echo "1+2*3" | /usr/share/antlr4/grun Calc expr -tree
Using the parser
Homework
(1 week)
- Hand-copy the grammar and turn in parse trees for 2 example inputs
