The following program does not compile correctly or type check correctly using the comp compiler and type inference system. However, it is a valid Standard ML program. Modify both the comp compiler and type checker to correctly compile and infer its type. This program is included in the compiler project as test20.sml.

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let val [(x, y, z)]= [(1+s+s2 (h) ellop (,)1, true)] in printin x end Output from the type checker should appear as follows. 1 Typechecking is commencing... 2 Here is the AST I 3 letdec (bindval (listpat ([ tuplepat ( [idpat (x),idpat (y), idpat (z)])]), listcon ( [tuple ([str ("hello"), int (1), bool(true) ])])), [apply (id (println), id (x))]) 4 5 6 val [(x, y, z)] : (str * int *bool) list 7 val it unit : 8 The program passed the typechecker. let val [(x, y, z)]= [(1+s+s2 (h) ellop (,)1, true)] in printin x end Output from the type checker should appear as follows. 1 Typechecking is commencing... 2 Here is the AST I 3 letdec (bindval (listpat ([ tuplepat ( [idpat (x),idpat (y), idpat (z)])]), listcon ( [tuple ([str ("hello"), int (1), bool(true) ])])), [apply (id (println), id (x))]) 4 5 6 val [(x, y, z)] : (str * int *bool) list 7 val it unit : 8 The program passed the typechecker.