- read_con data_con -- note: "b" is the string being "read"
- = let
- data_con_RDR = qual_orig_name data_con
- data_con_str= occNameString (getOccName data_con)
- con_arity = dataConNumFields data_con
- as_needed = take con_arity as_RDRs
- bs_needed = take con_arity bs_RDRs
- con_expr = mk_easy_App data_con_RDR as_needed
- nullary_con = isNullaryDataCon data_con
-
- con_qual
- = GeneratorQual
- (TuplePatIn [LitPatIn (HsString data_con_str), d_Pat])
- (HsApp (HsVar lex_RDR) c_Expr)
-
- field_quals = snd (mapAccumL mk_qual d_Expr (zipEqual "as_needed" as_needed bs_needed))
-
- read_paren_arg
- = if nullary_con then -- must be False (parens are surely optional)
- false_Expr
- else -- parens depend on precedence...
- HsPar (OpApp a_Expr (HsVar gt_RDR) (HsLit (HsInt 9)))
- in
- HsApp (
- readParen_Expr read_paren_arg $ HsPar $
- HsLam (mk_easy_Match tycon_loc [c_Pat] [] (
- ListComp (ExplicitTuple [con_expr,
- if null bs_needed then d_Expr else HsVar (last bs_needed)])
- (con_qual : field_quals)))
- ) (HsVar b_RDR)
- where
- mk_qual draw_from (con_field, str_left)
- = (HsVar str_left, -- what to draw from down the line...
- GeneratorQual
- (TuplePatIn [VarPatIn con_field, VarPatIn str_left])
- (HsApp (HsApp (HsVar readsPrec_RDR) (HsLit (HsInt 10))) draw_from))
+ stmts | is_infix = infix_stmts
+ | length labels > 0 = lbl_stmts
+ | otherwise = prefix_stmts
+
+ prefix_stmts -- T a b c
+ = [bindLex (ident_pat (data_con_str data_con))]
+ ++ map read_arg as_needed
+ ++ [result_stmt data_con as_needed]
+
+ infix_stmts -- a %% b
+ = [read_arg a1,
+ bindLex (symbol_pat (data_con_str data_con)),
+ read_arg a2,
+ result_stmt data_con [a1,a2]]
+
+ lbl_stmts -- T { f1 = a, f2 = b }
+ = [bindLex (ident_pat (data_con_str data_con)),
+ read_punc "{"]
+ ++ concat (intersperse [read_punc ","] field_stmts)
+ ++ [read_punc "}", result_stmt data_con as_needed]
+
+ field_stmts = zipWithEqual "lbl_stmts" read_field labels as_needed
+
+ con_arity = dataConSourceArity data_con
+ nullary_con = con_arity == 0
+ labels = dataConFieldLabels data_con
+ lab_fields = length labels
+ dc_nm = getName data_con
+ is_infix = isDataSymOcc (getOccName dc_nm)
+ as_needed = take con_arity as_RDRs
+ (a1:a2:_) = as_needed
+ prec = getPrec is_infix get_fixity dc_nm
+
+ ------------------------------------------------------------------------
+ -- Helpers
+ ------------------------------------------------------------------------
+ mk_alt e1 e2 = genOpApp e1 alt_RDR e2
+ bindLex pat = BindStmt pat (HsVar lexP_RDR) loc
+ result_stmt c as = ResultStmt (HsApp (HsVar returnM_RDR) (con_app c as)) loc
+ con_app c as = mkHsVarApps (getRdrName c) as
+
+ punc_pat s = ConPatIn punc_RDR (PrefixCon [LitPat (mkHsString s)]) -- Punc 'c'
+ ident_pat s = ConPatIn ident_RDR (PrefixCon [LitPat s]) -- Ident "foo"
+ symbol_pat s = ConPatIn symbol_RDR (PrefixCon [LitPat s]) -- Symbol ">>"
+
+ data_con_str con = mkHsString (occNameUserString (getOccName con))
+
+ read_punc c = bindLex (punc_pat c)
+ read_arg a = BindStmt (VarPat a) (mkHsVarApps step_RDR [readPrec_RDR]) loc
+
+ read_field lbl a = read_lbl lbl ++
+ [read_punc "=",
+ BindStmt (VarPat a) (mkHsVarApps reset_RDR [readPrec_RDR]) loc]
+
+ -- When reading field labels we might encounter
+ -- a = 3
+ -- _a = 3
+ -- or (#) = 4
+ -- Note the parens!
+ read_lbl lbl | is_id_start (head lbl_str)
+ = [bindLex (ident_pat lbl_lit)]
+ | otherwise
+ = [read_punc "(",
+ bindLex (symbol_pat lbl_lit),
+ read_punc ")"]
+ where
+ lbl_str = occNameUserString (getOccName (fieldLabelName lbl))
+ lbl_lit = mkHsString lbl_str
+ is_id_start c = isAlpha c || c == '_'