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edwinb / TypeDD-Samples

Sample code from "Type Driven Development with Idris"

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How does the inferring work on this line?

coodoo opened this issue · comments

commented

TypeDD-Samples/Chapter6/Printf.idr

Line 27 in a5c08a1

printf fmt = printfFmt _ "" 

Use an underscore (_) for the format, because Idris can infer from the type that it must be toFormat (unpack fmt).

This's the explanation from the book for above line but I'm still a bit puzzled by how does the inferring work here? Since fmt comes in as a String type, how does it become a Format type when passed to printfFmt?