Inverse Parser

Generate/compose text following a given grammar.

How to use

First, check/modify the Grammatical and Lexical Definition in folder grammar.

Then, launch a command line shell and run the following:

dotnet run

After that, each time you type enter, a new example will be generated:

Alice and Alice love cake.

Alice and Alice love banana. Bob loves banana. Bob loves cake. Bob and Bob love apple. Bob loves apple.

Alice and Alice love banana. Alice loves banana.

Bob and Alice love apple. Bob loves cake. Bob loves apple. Alice and Bob love cake. Alice loves apple. Bob loves apple. Alice and Bob love cake.

Grammar Definition

Two kind of files to define a grammar, namely grammatical definition file with extension gg and lexical definition file with extension gl.

Those files could be placed anywhere as long as the path is inside the folder GrammarDefinitionReader.RootDirectory. Besides, gg files or gl files could be many.

GrammarDefinitionReader.RootDirectory is currently defined as "./grammar" in Program.cs

A more complicated example could be found in folder grammar.

Rule

• Any text following # and before the nearest newline (i.e. \n) will be commented out
• A line started with # will be considered as a line with no char.
• Any "\n" in lexical token will be replaced with a newline

Grammatical Definition

The definition is written is BNF(Backus–Naur form)-like form.

Rule

• Allow arbitrary new blank lines.
• Tokens should be divided by space.
• The first token of a line is the left-hand side of the derivation.
  • the remaining tokens is the right-hand side of the derivation.
• Allow self referring.
• Allow same left-hand-side tokens in many lines. It represents all possible choice of derivations.
• If the token is not defined in the lexical definition file, it is considered as a literal token/terminal.

Example

# grammatical.gg

S A S
A B C
A B

...The derivation process start from S. the third line indicates that S will derivate A S. And the next line indicates that A will derivate B C. While the next line also indicates that A might also derivate B.

Lexical Definition

Rule

• blank lines to partition different non-terminals.
• A line started with # is also considered as a blank line.

Example

# lexical.gl

B
bbb
BBB

C
CCC
ccc

...It indicates that the non-terminal B could be derivated into terminals bbb or BBB. It is the same to C.

Result

With the example above, the results might be:

BBBbbbccc