Added some number formatting capability

README.md

@@ -7,6 +7,16 @@ When `format` is invoked on a string, placeholders within the string are
 replaced with values determined by the arguments provided. A placeholder
 is a sequence of characters beginning with `{` and ending with `}`.
 
+## About this Fork
+dchamber's original version implemented nested variable interpolation, and
+included support for _transformations_ that would provide functionality
+similar to the _conversions_ in python's str.format()
+
+It did not implement **printf()**-style number formatting, so here I'm attempting to do that.
+At the moment, only signs, integer precision, and field padding are implemented.
+
+## Usage
+
 ### string.format(value1, value2, ..., valueN)
 
 Placeholders may contain numbers which refer to positional arguments:

src/string-format.coffee

@@ -1,3 +1,13 @@
+# vim: ts=2:sw=2:expandtab
+###
+Source code and build tools for this file are available at:
+https://github.com/deleted/string-format
+
+This project attempts to implement python-style string formatting, as documented here:
+http://docs.python.org/2/library/string.html#format-string-syntax
+
+The format spec part is not complete, but it can handle field padding, float precision, and such
+###
 format = String::format = (args...) ->
 
   if args.length is 0
@@ -8,8 +18,8 @@ format = String::format = (args...) ->
   message = 'cannot switch from {} to {} numbering'.format()
 
   @replace \
-  /([{}])\1|[{](.*?)(?:!(.+?))?[}]/g,
-  (match, literal, key, transformer) ->
+  /([{}])\1|[{](.*?)(?:!([^:]+?)?)?(?::(.+?))?[}]/g,
+  (match, literal, key, transformer, formatSpec) ->
     return literal if literal
 
     if key.length
@@ -21,7 +31,10 @@ format = String::format = (args...) ->
       throw new Error message 'explicit', 'implicit' if explicit
       value = args[idx++] ? ''
 
-    value = value.toString()
+    if formatSpec
+        value = applyFormat(value,  formatSpec)
+    else
+      value = value.toString()
     if fn = format.transformers[transformer] then fn.call(value) ? ''
     else value
 
@@ -37,6 +50,70 @@ resolve = (object, key) ->
   value = object[key]
   if typeof value is 'function' then value.call object else value
 
-format.transformers = {}
+# An implementation of http://docs.python.org/2/library/string.html#format-specification-mini-language
+applyFormat = (value, formatSpec) ->
+  pattern = ///
+    ([^{}](?=[<>=^]))?([<>]^)? # fill & align
+    ([\+\-\x20])? # sign
+    (\#)? # integer base specifier
+    (0)? # zero-padding
+    (\d+)? # width
+    (,)? # use a comma thousands-seperator
+    (?:\.(\d+))? # precision
+    ([bcdeEfFgGnosxX%])? # type
+  ///
+  [fill, align, sign, hash, zeropad, width, comma, precision, type] = formatSpec.match(pattern)[1..]
+  if zeropad
+    fill = "0"
+    align = "="
+  if ! align
+    align = '>'
+
+  switch type
+    when 'b', 'c', 'd', 'o', 'x', 'X', 'n' # integer
+      isNumeric = true
+      value = '' + parseInt(value)
+    when 'e','E','f','F','g','G','n','%' # float
+      isNumeric = true
+      value = parseFloat(value)
+      if precision
+        value = value.toFixed(parseInt(precision))
+      else
+        value = ''+value
+    when 's' #string
+      isNumeric = false
+      value = '' + value
+
+  if isNumeric && sign
+    if sign in ["+"," "]
+        if value[0] != '-'
+          value = sign + value
+
+  if isNumeric && value[0] in "+-"
+    memoSign = value[0]
+    value = value[1..]
+
+  if fill
+    value = ''+value
+    while value.split('.')[0].length < parseInt(width)
+      switch align
+        when '='
+          if value[0] in "+- "
+            value = value[0] + fill + value[1..]
+          else
+            value = fill + value
+        when '<'
+          value = value + fill
+        when '>'
+          value = fill + value
+        when '^'
+          throw new Error("Not implemented")
+
+  if memoSign
+    value = memoSign + value
+
+  return value
+
+format.transformers = format.transformers || {}
 
 format.version = '0.2.1'

test/string-format.coffee

@@ -101,3 +101,9 @@ describe 'String::format', ->
     '{{{{0}}}}'.format(null).should.equal '{{0}}'
     '}}{{'.format(null).should.equal '}{'
     '}}x{{'.format(null).should.equal '}x{'
+
+  it "correctly formats floats", ->
+    '{:0}'.format(1.2345).should.equal '1.2345'
+    '{:03.2f}'.format(1.2345).should.equal '001.23'
+    '{:03.2f}'.format(-1.2345).should.equal '-001.23'
+    '{:+02.3f}'.format(1.2345).should.equal '+01.234'