Domain Specific Languages

I still see old world flat file specifications like the following:

Type	Name	Description
9(8)	Some Date	DDMMYYYY
9(6)	Some Time	HHMMSS
x(20)	Lovely Name	A Good Name
x(36)	filler	Ignore

I thought I would do something different implement the parser as if I was a Lisper. So, here's what I came up with:

recordLayout
 ^#(
  (9(8) someDate asDDMMYYYY)
  (9(6) someTime asHHMMSS)
  (x(20) lovelyName)
  (x36) filler)
)

And what does the code look like to parse it? It's even simpler than I thought:

parse: aStream
 self recordLayout do: [:eachLayout | | typeInfo typeLength fieldName converterSelector rawData data |
  typeInfo := eachLayout first.
  typeLength := eachLayout second first.
  fieldName := eachLayout third.
  converterSelector := eachLayout at: 4 ifAbsent: [#yourself].
  rawData := aStream next: typeLength.
  (typeInfo == 9) ifTrue: [self verifyIsNumeric: rawData].
  data := rawData perform: converterSelector.
  self perform: (self setterFor: fieldName) with: data]

WOW! I now have a method that shows the record layout that could be parsed for creating test records as well. I could even show it to a non-Smalltalker and they would know what's going on. I love the flexibility of Smalltalk! I love adding new tricks to my bag.