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MONETARY LIBRARY

Monetary string formatting library in Teal (and Lua).

Overview

Monetary is a pure-Teal library for string formatting numbers as currency. It is very similar (but not identical to) strfmon as defined by GNU[1].

This library does not use the system locale. Instead we give a rough approximation by allowing the user to define the symbols used for the thousands separator, the decimal point, and currency symbol; which the default is ,, ., and $ respectively.

The library provides two functions, as shown by the record definition:

local type M = record
  localize: function(thou: string, dec: string, cur: string)
  strfmon:  function(fmt: string, val: number): string
end

Example Use

Say we want to format numbers for printing like:

$    10,499.50
$ 1,234,567.00

Or without cents, rounding the values:

$    10,500
$ 1,234,567

Localized:

€    10.499,50
€ 1.234.567,00

€    10.500
€ 1.234.567

We can use code as shown in doc_monetary.tl.

doc_monetary.tl

local m = require "monetary"
local strfmon = m.strfmon
local localize = m.localize

local val1 = 10499.50
local val2 = 1234567

local fmt1 = "%#8.2n"    -- 8 digits to left of decimal; 2 to right
local fmt2 = "%#8.0n"    --               "            ; 0 to right

print( strfmon(fmt1, val1) )   -- $    10,499.50
print( strfmon(fmt1, val2) )   -- $ 1,234,567.00
print()
print( strfmon(fmt2, val1) )   -- $    10,500
print( strfmon(fmt2, val2) )   -- $ 1,234,567

print()
print("localized...")
localize(".",",","€")

print( strfmon(fmt1, val1) )   -- €    10.499,50
print( strfmon(fmt1, val2) )   -- € 1.234.567,00
print()
print( strfmon(fmt2, val1) )   -- €    10.500
print( strfmon(fmt2, val2) )   -- € 1.234.567

Functions

localize(thou: string, dec: string, cur: string)

localize is used to set the separators used in the formatted string and the currency symbol. The library defaults to , for thousands, . for decimal point and $ for currency. To override these defaults call localize with the desired separators.

For example, to set . as thousands, , as decimal point and € for currency:

localize(".", ",", "€")

strfmon(fmt: string, val: number): string

strfmon is used to format a number as currency. It returns a string.

The fmt argument has a number of optional flags between the required opening '%' and closing 'n'. They are, in order:

'^'      Turn off use of thousands grouping. By default grouping is enabled.

'+','('  At most one of these is allowed. '+' is the default, which formats
         negative numbers using '-'. (note: '+' is the flag, and not '-',
         since '-' is used to indicate "left-justification".) To indicate
         negative numbers by enclosing them in parenthesis use the '(' flag.

'!'      Turn off use of currency symbol. Currency symbol is on by default.

'-'      The output is left-justified. By default output is right-justified.
         Justificaiton is only relevant when the entire field isn't filled.

<w>      Minimum width of return string. If it is missing then default of 0
         is used, which means any width is ok, and no padding is relevant, nor
         is any justification relevant. If a width is given, and the output is
         less than the width, the output is padded with spaces (on the left,
         by default, on the right when '-' (left-justification) is enabled) in
         order to make the output be <w> characters wide.

'#'      Activates the context for (left-of) or (left-of and right-of) spacing
         relevant to the decimal point (as opposed to spacing for the overall
         field, which is driven by <w> above). By default this context is not
         active.

         If the context is enabled then at least the <l> field is
         required. If the '.' symbol is included then the <r> field is
         required.

         <l>   Left-of decimal point minimum width, as measured in *digits*.
               Ensures that space for at least <l> number of digits is
               provided. If thousands grouping is enabled, then space for
               those is also included (this space is not counted as a
               'digit'). For example, #6 for a value of 1000 will create a
               string "$  1,000", having ensured space for 6 digits.

        '.'    Seperates "left-of" from "right-of" decimal fields.

        <r>    Right-of decimal point minimum width, as measured in *digits*.
               If <r> is 0, then no decimal point appears in the output, and
               the value is rounded to be an integer. For other values of <r>
               0's are padded to fill out the minimum width, or, if the
               decimal portion exceeds <r> then the floating portion is
               rounded to <r> places.

References

[1] https://www.gnu.org/software/libc/manual/html_node/Formatting-Numbers.html