Difference between revisions of "DDC/FieldProjections"
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| − | == Data |
+ | == Data fields == |
When data types are defined using field names, we can use the projection operator <hask>(.)</hask> to select the fields. |
When data types are defined using field names, we can use the projection operator <hask>(.)</hask> to select the fields. |
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instance Out Vector where |
instance Out Vector where |
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| − | out vec = println $ parens (show x % "," % show y) |
+ | out vec = println $ parens (show vec.x % "," % show vec.y) |
main () |
main () |
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| Line 16: | Line 16: | ||
out vec.x -- prints '3.0' |
out vec.x -- prints '3.0' |
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out vec.y -- prints '4.0' |
out vec.y -- prints '4.0' |
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| − | |||
</haskell> |
</haskell> |
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| + | |||
| + | == Custom projections == |
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Revision as of 11:24, 18 March 2008
Data fields
When data types are defined using field names, we can use the projection operator (.) to select the fields.
data Vector
= Vector { x :: Float; y :: Float; }
instance Out Vector where
out vec = println $ parens (show vec.x % "," % show vec.y)
main ()
= do vec = Vector 3.0 4.0
out vec -- prints '(3.0, 4.0)'
out vec.x -- prints '3.0'
out vec.y -- prints '4.0'