1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 |
------------------------------------------------------------------------------ --- Library for converting ground terms to strings and vice versa. --- --- Remark: The `Data` type class constraint is removed for KiCS2 --- since this causes a memory leak (due to the non-deterministic method --- `aValue`) but it is not used in the implementation. --- --- @author Michael Hanus --- @version October 2024 ------------------------------------------------------------------------------ {-# LANGUAGE CPP #-} module ReadShowTerm ( showTerm, readsUnqualifiedTerm, readUnqualifiedTerm ) where import Data.Char ( isSpace ) --- Transforms a ground(!) data term into a string representation --- in standard prefix notation. --- Thus, `showTerm` suspends until its argument is ground. --- This function is similar to the prelude function `show` --- but can read the string back with `readUnqualifiedTerm` --- (provided that the constructor names are unique without the module --- qualifier). showTerm :: Data a => a -> String showTerm x = prim_showTerm $## x prim_showTerm :: _ -> String prim_showTerm external --- Transform a string containing a data term in standard prefix notation --- without module qualifiers into the corresponding data term. --- The first argument is a non-empty list of module qualifiers --- that are tried to prefix the constructor in the string --- in order to get the qualified constructors --- (that must be defined in the current program!). --- In case of a successful parse, the result is a one element list --- containing a pair of the data term and the remaining unparsed string. readsUnqualifiedTerm :: Data a => [String] -> String -> [(a,String)] readsUnqualifiedTerm [] _ = error "ReadShowTerm.readsUnqualifiedTerm: list of module prefixes is empty" readsUnqualifiedTerm (prefix:prefixes) s = readsUnqualifiedTermWithPrefixes (prefix:prefixes) s readsUnqualifiedTermWithPrefixes :: Data a => [String] -> String -> [(a,String)] readsUnqualifiedTermWithPrefixes prefixes s = (prim_readsUnqualifiedTerm $## prefixes) $## s prim_readsUnqualifiedTerm :: [String] -> String -> [(_,String)] prim_readsUnqualifiedTerm external --- Transforms a string containing a data term in standard prefix notation --- without module qualifiers into the corresponding data term. --- The first argument is a non-empty list of module qualifiers --- that are tried to prefix the constructor in the string --- in order to get the qualified constructors --- (that must be defined in the current program!). --- --- Example: `readUnqualifiedTerm ["Prelude"] "Just 3"` evaluates to `(Just 3)` readUnqualifiedTerm :: Data a => [String] -> String -> a readUnqualifiedTerm prefixes s = case result of [(term,tail)] -> if all isSpace tail then term else error $ "ReadShowTerm.readUnqualifiedTerm: no parse, " ++ "unmatched string after term: " ++ tail [] -> error "ReadShowTerm.readUnqualifiedTerm: no parse" _ -> error "ReadShowTerm.readUnqualifiedTerm: ambiguous parse" where result = readsUnqualifiedTerm prefixes s |