1
Q
Role of parser
A
- obtains a string from the lexical analyser and verifies if the given string can be constructed using the given grammar
- it should also be able to recover from common errors and must continue forward
- constructs a parse tree and passes it to the rest of the compiler for further processing
2
Q
Types of parsing
A
- top down: constructs the parse tree from the top (root node) to the bottom (leaf node)
- bottom up: constructs a syntax tree from the bottom (leaf node) to the top (root node)
3
Q
Different errors in parsing
A
- lexical: includes misspellings of identifiers
- syntactic: includes misplaced semicolon and missing braces
- semantic: includes type mismatch between operator and operands
- logical: includes any thing from incorrect reasoning on the part of the programmer
4
Q
Error recovery techniques
A
- panic mode recoverywith this method, on discovering an error, the parser discards input symbols one at a time until one of the set of tokens is found
- parse level recoveryon discovering an error, a parser performs a local correction on the remaining input. usually done by replacing the input by some string that allows the parsing to continue
- error productionin this method, common errors that might be encountered can be add those productions into the grammar to perform the required action for the same
- global correctionalgorithms that choose a minimal sequence of changes to obtain a globally least cost correction
5
Q
what is a parse tree
A
- it is a graphical representation of the derivation which shows the order in which the productions are applied to replace non-terminals
- each interior node of the syntax tree represents the application of a particular production
6
Q
what is ambiguity
A
- any grammar that produces more than one parse tree for some given input.
- in another way, an ambiguous grammar produces more than one leftmost or rightmost derived grammar for the same input
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