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Results tagged with context-free
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user 988
Context-free languages and grammars.
29
votes
3
answers
3k
views
Does there exist an extension of regular expressions that captures the context free languages?
In many papers involving context-free grammars (CFGs), the examples of such grammars presented there often admit easy characterizations of the language they generate. For example:
$S \to a a S b$
…
- 4,730
8
votes
0
answers
1k
views
Is there an ambiguity test for CFGs faster than trying all strings?
It is well known that testing whether a grammar is ambiguous is undecidable. It is however trivially decidable for any $G$ whether $L_n(G) := \{ w | w \in L(G) \wedge |w| \leq n \}$ for any $n \in \ma …
- 4,730
23
votes
1
answer
2k
views
Can all unambiguous grammars be parsed in linear time?
When tinkering with noncanonical LR parsing, I thought up a parsing method (with infinitely sized tables, which makes it somewhat unpractical) capable of parsing exactly the unambiguous grammars in $O …
- 4,730
16
votes
2
answers
2k
views
Permutation phrases with LR parsing
A permutation phrase is an extension to the standard (E)BNF context free grammar definitions: a permutation phrase $\{ A_1, \dots, A_n \}$ contains $n$ productions (or equivalently, nonterminals) $A_1 …
- 4,730
19
votes
3
answers
756
views
CFG parsing using $o(n^2)$ space
There are a multitude of algorithms that can parse a context-free grammar in $O(n^3)$ time. Using matrix multiplication, one can even go asymptotically faster than that.
However, all algorithms for p …
- 4,730