Trouble with PEG.js end of input

Question

I am trying to write a simple grammer for PEG.js that would match something like this:

some text;
arbitrary other text that can also have µnicode; different expression;
let's escape the \; semicolon, and \not recognized escapes are not a problem;
possibly last expression not ending with semicolon

So basically these are some texts separated by semicolons. My simplified grammer looks like this:

start
= flow:Flow

Flow
= instructions:Instruction*

Instruction
= Empty / Text

TextCharacter
= "\\;" /
.

Text
= text:TextCharacter+ ';' {return text.join('')}

Empty
= Semicolon

Semicolon "semicolon"
= ';'

The problem is that if I put anything other than a semicolon in the input, I get:

SyntaxError: Expected ";", "\\;" or any character but end of input found.

How to solve this? I've read that PEG.js is unable to match end of input.

Zootoxin

FWIW, you can match end of input with !. – Chancellorsville

Answer 1

You have (at least) 2 problems:

Your TextCharacter should not match any character (the .). It should match any character except a backslash and semi-colon, or it should match an escaped character:

TextCharacter
 = [^\\;]
 / "\\" .

The second problem is that your grammar mandates your input to end with a semi-colon (but your input does not end with a ;).

How about something like this instead:

start
 = instructions

instructions
 = instruction (";" instruction)* ";"?

instruction
 = chars:char+ {return chars.join("").trim();}

char
 = [^\\;]
 / "\\" c:. {return ""+c;}

which would parse your input as follows:

[
   "some text",
   [
      [
         ";",
         "arbitrary other text that can also have µnicode"
      ],
      [
         ";",
         "different expression"
      ],
      [
         ";",
         "let's escape the ; semicolon, and not recognized escapes are not a problem"
      ],
      [
         ";",
         "possibly last expression not ending with semicolon"
      ]
   ]
]

Note that the trailing semi-colon is optional now.

Laurentian