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Saturday, September 10, 2005
Domain Specific Languages
I still see old world flat file specifications like the following:
I thought I would do something different implement the parser as if I was a Lisper. So, here's what I came up with:
And what does the code look like to parse it? It's even simpler than I thought:
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.
| 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.
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