Nelly

GitHub

Installation

$ pip install nelly

Simple Example

<%pre
    import sys
%>

::NT(start)
    : 'A' # comment
    | 'B' <% print $$ %>
    ;

<%post
    print $$
%>

Constants

Constants in productions can consist of double-quoted strings, single-quoted strings, decimal, hexadecimal, or octal numbers.

A: "A" | 'A' | 65 | 0x41 | 0101;

Concatenation

Productions are concatenated when they are seperated by white-space.

CONCAT: "CONC" 0x41 "TEN" 65 "TION";

The generated output is CONCATENATION

Selection

When multiple productions are present one is chosen at random.

NUMBER: '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9';

Grouping

GRP: ('A'|'B') ('C'|'D');

Possible values are AC, AD, BC, or BD.

Ranges

NUM1: ('0'|'1'|'2'|'3'|'4'|'5'|'6'|'7'|'8'|'9'){3};
NUM2: ('0'|'1'|'2'|'3'|'4'|'5'|'6'|'7'|'8'|'9'){1,5};

NUM1 will generate a 3-digit number while NUM2 will generate a number of random length between 1 and 5 digits.

Slicing

A sub-string of a production can be referenced using indices.

SLICE1: "0123456789" [:];    // 0123456789
SLICE2: "0123456789" [4];    // 4
SLICE3: "0123456789" [:4];   // 0123
SLICE4: "0123456789" [4:];   // 456789
SLICE5: "0123456789" [2:8];  // 234567
SLICE6: "0123456789" [-4];   // 6
SLICE7: "0123456789" [-4:];  // 6789
SLICE8: "0123456789" [:-4];  // 012345
SLICE9: "0123456789" [2:-2]; // 234567

The output of each production is documented in the comment proceeding it.

Inline Python

<%pre
    import base64
%>

NT: %base64.b64encode('string');

Non-Terminals

NT1: "The value of NT2 is " NT2;
NT2: "substitution";

Semantic Actions

$$

PSA1: PSA2 <% var = $$ %>;
PSA2: "one" | "two";

In this example PSA1 and the Python variable var will contain either 'one' or 'two' for future use.

Variable Non-Terminals

$*

NT1: $NT2;

$NT2:
  "I WILL BE SUBSTITUTED INTO NT1 IN LOWERCASE"
  <%
    $* = $$.lower()
  %>
  ;

Back Reference

BR: "A" | "B";
NT: BR \BR;

$BR: ("a"|"b") <% $* = $$.upper() %>;
NT: $BR \$BR;

NT will generate the string AA or BB but not AB or BA.