用数据结构在haskell中进行漂亮的打印

Question

I am the beginner of Haskell, and I want to make a pretty printing with data structures in Haskell.

I have the following data structure:

https://codeshare.io/5zl9WD

I want to print the following value:

int a(int b, int* c){
   return b + *c;
}

by using the following function types:

pFunc :: f -> document

putStrLn $ pretty 40 $ pFunc fun

fun =("a", TInt, [(TInt, "b"),(TPtr TInt, "c")]
      , [SReturn (EBinOp "+" (EIdent "b") (EUnOpPre "*" (EIdent "c")))])

document data structure is as the following:

https://codeshare.io/G64gyg

But honestly I don't have any idea. I have many similar simple printings. If I can have an idea about this printing, the remaining one won't be a problem.

But might be the shortest way to print the value above by using document data type?

Answer 1

Write a pretty-printer function for each of the types in the abstract-syntax-tree. Each function will have type:

pretty<Foo> :: <Foo> -> Document

where you replace <Foo> with the type name. Work bottom up, so you can test each function as you write it. ie implement the pretty-printer for Type first, since it is needed by the pretty-printer for Stmt and f (which should be called Func or something).

For instance:

prettyType :: Type -> Document
prettyType TVoid     = text "void"
prettyType TInt      = text "int"
prettyType TFloat    = text "float"
prettyType TChar     = text "char"
prettyType TPtr t    = prettyType t <> text "*"
prettyType TStruct s = text "struct" <+> text s

Follow the same pattern for each of Exp , Stmt , Case , and Func .