[Swift-devel] type-checking mappers

[Ben Clifford]

In the context of bug 152, I have thought a little about type checking 
mappers. Some mappers are amenable to compile-time type checking - for 
example, the single-file mapper can only map a simple unstructured type; 
the filesys-mapper can only map a single dimensional array of unstructured 
types. Not all mappers seem to work with this - for example the external 
mapper can map any shape structure.

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