Go Ledger parser

Short term goal: parse relatively complex Ledger files, and provide an abstract syntax tree (a full programmatic representation of the file), to be able to tweak some parts programmatically, and then write back the files to disk.

ledgerfmt, similar to gofmt, parses the input file, indents and aligns according to conventions, and outputs the file back, without any semantic changes or interpretation of the data.
ledger2json parses your Ledger file and outputs a .json file, which you can manipulate with any software.
json2ledger will read the same file, and produce a .ledger file, properly formatted (not yet implemented)

Longer term goal: do the mathematical computations of the original Ledger program.

Installation

Have Go installed (from https://golang.org/dl), then run:

go get -u github.com/abourget/ledger/cmd/ledgerfmt

Emacs bindings are pending at the original https://github.com/ledger/ledger repo (in a PR).

`ledgerfmt`

Input:

2016/01/01=2016.02/02 Tx
  Account1:Hello World     10.00$    @   12.23 USD  ; Note 7 flames
  Other                    (123 USD)  ; Note

2016/01/01 !Tx
  Account1:Hello World          $10.00 [2017/01/01]  ; Then comment
  ! Other  ; Comment here
  ; Comment there

2017/01/01 * Tx
 Account1:Hello World        - 10.00 $
 Other                   (10.00 $ * 2)

reformats to:

2016-01-01 = 2016-02-02Tx
    Account1:Hello World              10.00 $ @ 12.23 USD  ; Note 7 flames
    Other                             (123 USD)  ; Note

2016-01-01 ! Tx
    Account1:Hello World              10.00 $ [2017-01-01]  ; Then comment
    ! Other; Comment here
    ; Comment there

2017-01-01 * Tx
    Account1:Hello World              -10.00 $
    Other                             (10.00 $ * 2)

`ledger2json`

For a simple example, see the parse_test.go file. Here is an excerpt:

; Top level comment

2016/09/09 = 2016-09-10 * Kentucky Friends Beef      ; Never go back there
   ; Some more notes for the transaction
  Expenses:Restaurants    20.00 CAD
  Assets:Cash             CAD -20.00    ; That hurt


2016/09/09 ! Payee
  ; Transaction notes
  Expenses:Misc    20.00 CAD
  Assets:Cash  ; Woah, not sure
 ; Here again
  ; And yet another note for this posting.

2016/09/10 Desc
  A  - $ 23
  B  23 $ @ 2 CAD

outputs:

{
  "NodeType": 1,
  "Pos": 0,
  "Nodes": [
    {
      "NodeType": 4,
      "Pos": 0,
      "Comment": "; Top level comment"
    },
    {
      "NodeType": 5,
      "Pos": 20,
      "Space": "\n"
    },
    {
      "NodeType": 2,
      "Pos": 21,
      "Date": "2016-09-09T00:00:00Z",
      "EffectiveDate": "2016-09-10T00:00:00Z",
      "Description": "Kentucky Friends Beef      ",
      "IsPending": false,
      "IsCleared": true,
      "NotePreSpace": "",
      "Note": "; Never go back there\n; Some more notes for the transaction",
      "Postings": [
        {
          "NodeType": 3,
          "Pos": 139,
          "AccountPreSpace": "",
          "Account": "Expenses:Restaurants",
          "AccountPostSpace": "    ",
          "Amount": {
            "NodeType": 6,
            "Pos": 163,
            "Raw": "20.00 CAD",
            "Quantity": "20.00",
            "Negative": false,
            "Commodity": "CAD",
            "ValueExpr": ""
          },
          "BalanceAssertion": "",
          "BalanceAssignment": "",
          "Price": null,
          "PriceIsForWhole": false,
          "LotDate": "0001-01-01T00:00:00Z",
          "LotPrice": null,
          "NotePreSpace": "",
          "Note": ""
        },
        {
          "NodeType": 3,
          "Pos": 175,
          "AccountPreSpace": "",
          "Account": "Assets:Cash",
          "AccountPostSpace": "             ",
          "Amount": {
            "NodeType": 6,
            "Pos": 199,
            "Raw": "CAD -20.00",
            "Quantity": "20.00",
            "Negative": true,
            "Commodity": "CAD",
            "ValueExpr": ""
          },
          "BalanceAssertion": "",
          "BalanceAssignment": "",
          "Price": null,
          "PriceIsForWhole": false,
          "LotDate": "0001-01-01T00:00:00Z",
          "LotPrice": null,
          "NotePreSpace": "",
          "Note": "; That hurt"
        }
      ]
    },
    {
      "NodeType": 5,
      "Pos": 225,
      "Space": "\n\n"
    },
    {
      "NodeType": 2,
      "Pos": 227,
      "Date": "2016-09-09T00:00:00Z",
      "EffectiveDate": "0001-01-01T00:00:00Z",
      "Description": "Payee",
      "IsPending": true,
      "IsCleared": false,
      "NotePreSpace": "",
      "Note": "; Transaction notes",
      "Postings": [
        {
          "NodeType": 3,
          "Pos": 270,
          "AccountPreSpace": "",
          "Account": "Expenses:Misc",
          "AccountPostSpace": "    ",
          "Amount": {
            "NodeType": 6,
            "Pos": 287,
            "Raw": "20.00 CAD",
            "Quantity": "20.00",
            "Negative": false,
            "Commodity": "CAD",
            "ValueExpr": ""
          },
          "BalanceAssertion": "",
          "BalanceAssignment": "",
          "Price": null,
          "PriceIsForWhole": false,
          "LotDate": "0001-01-01T00:00:00Z",
          "LotPrice": null,
          "NotePreSpace": "",
          "Note": ""
        },
        {
          "NodeType": 3,
          "Pos": 299,
          "AccountPreSpace": "",
          "Account": "Assets:Cash",
          "AccountPostSpace": "  ",
          "Amount": null,
          "BalanceAssertion": "",
          "BalanceAssignment": "",
          "Price": null,
          "PriceIsForWhole": false,
          "LotDate": "0001-01-01T00:00:00Z",
          "LotPrice": null,
          "NotePreSpace": "",
          "Note": "; Woah, not sure\n; Here again\n; And yet another note for this posting."
        }
      ]
    },
    {
      "NodeType": 5,
      "Pos": 386,
      "Space": "\n"
    },
    {
      "NodeType": 2,
      "Pos": 387,
      "Date": "2016-09-10T00:00:00Z",
      "EffectiveDate": "0001-01-01T00:00:00Z",
      "Description": "Desc",
      "IsPending": false,
      "IsCleared": false,
      "NotePreSpace": "",
      "Note": "",
      "Postings": [
        {
          "NodeType": 3,
          "Pos": 405,
          "AccountPreSpace": "",
          "Account": "A",
          "AccountPostSpace": "  ",
          "Amount": {
            "NodeType": 6,
            "Pos": 408,
            "Raw": "- $ 23",
            "Quantity": "23",
            "Negative": true,
            "Commodity": "$",
            "ValueExpr": ""
          },
          "BalanceAssertion": "",
          "BalanceAssignment": "",
          "Price": null,
          "PriceIsForWhole": false,
          "LotDate": "0001-01-01T00:00:00Z",
          "LotPrice": null,
          "NotePreSpace": "",
          "Note": ""
        },
        {
          "NodeType": 3,
          "Pos": 417,
          "AccountPreSpace": "",
          "Account": "B",
          "AccountPostSpace": "  ",
          "Amount": {
            "NodeType": 6,
            "Pos": 420,
            "Raw": "23 $",
            "Quantity": "23",
            "Negative": false,
            "Commodity": "$",
            "ValueExpr": ""
          },
          "BalanceAssertion": "",
          "BalanceAssignment": "",
          "Price": {
            "NodeType": 6,
            "Pos": 426,
            "Raw": " 2 CAD",
            "Quantity": "2",
            "Negative": false,
            "Commodity": "CAD",
            "ValueExpr": ""
          },
          "PriceIsForWhole": false,
          "LotDate": "0001-01-01T00:00:00Z",
          "LotPrice": null,
          "NotePreSpace": "",
          "Note": ""
        }
      ]
    }
  ]
}

Shortcomings

This implementation has a few limitations compared to the C++ version:

It does not yet support all top-level constructs, like "account", "alias", "P", "D", "year" / "Y", etc.. Most of those should be simple to implement.
It does not yet understand tags. They are only considered comments.
It does not yet implement the value_expr language that allows you to do complex math computations directly in the postings of your transactions. It merely store the string text of the expression, PROVIDED it is enclosed in parenthesis, e.g. (123 + 2 * 3 USD).
Also note that the current implementation does not validate any balances. It merely acts on the text of the file.

References

The lexer is heavily based on Go's text/template. Also this talk by Rob Pike inspired me: https://www.youtube.com/watch?v=HxaD_trXwRE
https://github.com/howeyc/ledger for a simpler Go parser, but with some other features.
http://plaintextaccounting.org/ for more fun about Ledger files

glasser / ledger