add unit type

git-svn-id: https://svn.cs.ru.nl/repos/clean-compiler/trunk@2365 1f8540f1-abd5-4d5b-9d24-4c5ce8603e2d

6 files changed, 329 insertions, 234 deletions

diff --git a/backend/backendconvert.icl b/backend/backendconvert.icl
index 3392c9d..156358a 100644
--- a/backend/backendconvert.icl
+++ b/backend/backendconvert.icl
@@ -917,6 +917,24 @@ declareDynamicTemp :: PredefinedSymbols -> BackEnder
 declareDynamicTemp predefs
 	=	appBackEnd (BEDeclareDynamicTypeSymbol predefs.[PD_StdDynamic].pds_def predefs.[PD_Dyn_DynamicTemp].pds_def)
 
+^= v be
+	:== (v,be)
+
+@^ f f1 be
+	# (v1,be) = f1 be
+	:== f v1 be
+
+@^^ f f1 f2 be
+	# (v1,be) = f1 be
+	  (v2,be) = f2 be
+	:== f v1 v2 be
+
+@^^^ f f1 f2 f3 be
+	# (v1,be) = f1 be
+	  (v2,be) = f2 be
+	  (v3,be) = f3 be
+	:== f v1 v2 v3 be
+
 predefineSymbols :: DclModule PredefinedSymbols -> BackEnder
 predefineSymbols {dcl_common} predefs
 	=	appBackEnd (BEDeclarePredefinedModule (size dcl_common.com_type_defs) (size dcl_common.com_cons_defs))
@@ -924,6 +942,7 @@ predefineSymbols {dcl_common} predefs
 	o`	foldState predefineType types
 	o`	foldState predefine_list_constructor list_constructors
 	o`	foldState predefineConstructor constructors
+	o`	define_unit_type
 	where
 		list_types :: [(Int,Int,Int)]
 		list_types
@@ -997,6 +1016,16 @@ predefineSymbols {dcl_common} predefs
 			// ... sanity check
 			=	appBackEnd (BEPredefineConstructorSymbol arity predefs.[index].pds_def cPredefinedModuleIndex symbolKind)
 
+		define_unit_type
+			# constructor_symbol_be_f = BEConstructorSymbol predefs.[PD_UnitConsSymbol].pds_def cPredefinedModuleIndex
+			  type_be_f = @^^ BENormalTypeNode constructor_symbol_be_f BENoTypeArgs
+			  constructors_be_f = @^^ BEConstructors (@^ BEConstructor type_be_f) BENoConstructors
+			  type_symbol_be_f = BETypeSymbol predefs.[PD_UnitType].pds_def cPredefinedModuleIndex
+			  flat_type_be_f = @^^^ BEFlatType type_symbol_be_f (^= BENoUniAttr) BENoTypeVars
+			= appBackEnd
+				(  BEDeclareConstructor predefs.[PD_UnitConsSymbol].pds_def cPredefinedModuleIndex "_Unit"
+			  	o` BEDeclareType predefs.[PD_UnitType].pds_def cPredefinedModuleIndex "_Unit"
+				o` @^^ BEAlgebraicType flat_type_be_f constructors_be_f)
 
 bindSpecialIdents :: PredefinedSymbols NumberSet -> BackEnder
 bindSpecialIdents predefs usedModules
diff --git a/frontend/check.icl b/frontend/check.icl
index 232b44e..36b797f 100644
--- a/frontend/check.icl
+++ b/frontend/check.icl
@@ -3330,8 +3330,8 @@ where
 				<=< adjustPredefSymbolAndCheckIndex PD_StringType mod_index PD_StringTypeIndex STE_Type
 				<=< adjust_predef_symbols PD_ListType PD_OverloadedListType mod_index STE_Type
 				<=< adjust_predef_symbols_and_check_indices PD_Arity2TupleType PD_Arity32TupleType PD_Arity2TupleTypeIndex mod_index STE_Type
-				<=< adjust_predef_symbols PD_LazyArrayType PD_UnboxedArrayType mod_index STE_Type
-				<=< adjust_predef_symbols PD_ConsSymbol PD_Arity32TupleSymbol mod_index STE_Constructor
+				<=< adjust_predef_symbols PD_LazyArrayType PD_UnitType mod_index STE_Type
+				<=< adjust_predef_symbols PD_ConsSymbol PD_UnitConsSymbol mod_index STE_Constructor
 				<=< (if tc_class_defined (adjustPredefSymbol PD_TypeCodeClass mod_index STE_Class) (\x->x))
 				<=< (if tc_class_defined (adjustPredefSymbol PD_TypeCodeMember mod_index STE_Member) (\x->x))
 				<=< adjustPredefSymbol PD_DummyForStrictAliasFun mod_index STE_DclFunction)
@@ -3356,7 +3356,7 @@ where
 				<=< adjust_predef_symbols PD_Dyn_initial_unification_environment PD_Dyn_normalise mod_index STE_DclFunction
 				<=< adjustPredefSymbol PD_Dyn__to_TypeCodeConstructor	mod_index STE_DclFunction
 				<=< adjustPredefSymbol PD_TypeCodeConstructor mod_index STE_Type
-				<=< adjust_predef_symbols PD_TC_Int PD_TC__UnboxedArray mod_index STE_Constructor
+				<=< adjust_predef_symbols PD_TC_Int PD_TC__Unit mod_index STE_Constructor
 				)
 		# (pre_mod, cs_predef_symbols) = cs_predef_symbols![PD_StdGeneric]
 		# type_bimap = predefined_idents.[PD_TypeBimap]	
diff --git a/frontend/convertDynamics.icl b/frontend/convertDynamics.icl
index 2ce916e..bbe667d 100644
--- a/frontend/convertDynamics.icl
+++ b/frontend/convertDynamics.icl
@@ -560,6 +560,8 @@ where
 					-> type_code_constructor_expression PD_TC__StrictArray ci
 				PD_UnboxedArrayType
 					-> type_code_constructor_expression PD_TC__UnboxedArray ci
+				PD_UnitType
+					-> type_code_constructor_expression PD_TC__Unit ci
 	typeConstructor (GTT_Constructor fun_ident _) ci
 		# type_fun
 			=	App {app_symb = fun_ident, app_args = [], app_info_ptr = nilPtr}
diff --git a/frontend/parse.icl b/frontend/parse.icl
index a7147da..0b02282 100644
--- a/frontend/parse.icl
+++ b/frontend/parse.icl
@@ -2964,6 +2964,9 @@ trySimpleTypeT_after_OpenToken ArrowToken attr pState
 		= (ParseOk, {at_attribute = attr, at_type = TArrow}, pState)
 		= (ParseFailWithError,{at_attribute = attr, at_type = TE},
 			parseError "arrow type" (Yes token) ")" pState)
+trySimpleTypeT_after_OpenToken CloseToken attr pState
+	#! unit_type_ident = predefined_idents.[PD_UnitType]
+	= (ParseOk,{at_attribute=attr,at_type=TA (MakeNewTypeSymbIdent unit_type_ident 0) []},pState)
 trySimpleTypeT_after_OpenToken token attr pState
 	# (annot_with_pos,atype, pState) = wantAnnotatedATypeWithPositionT token pState
 	  (token, pState)	= nextToken TypeContext pState
@@ -3387,19 +3390,37 @@ trySimplePatternT SquareOpenToken pState
 	# (list_expr, pState) = wantListExp cIsAPattern pState
 	= (True, list_expr, pState)
 trySimplePatternT OpenToken pState
-	# (args=:[exp:exps], pState) = want_pattern_list pState
-	  pState = wantToken FunctionContext "pattern list" CloseToken pState
-	| isEmpty exps
-		= case exp of
-			PE_Ident id
-				-> (True, PE_List [exp], pState)
-			_
-				-> (True, exp, pState)
-		= (True, PE_Tuple args, pState)
+	# (token, pState) = nextToken FunctionContext pState
+	= case token of
+		CloseToken
+			#! unit_cons_ident = predefined_idents.[PD_UnitConsSymbol]
+			-> (True,PE_Ident unit_cons_ident,pState)
+		_
+			# (args=:[exp:exps], pState) = want_pattern_list_t token pState
+			  pState = wantToken FunctionContext "pattern list" CloseToken pState
+			| isEmpty exps
+				-> case exp of
+					PE_Ident id
+						-> (True, PE_List [exp], pState)
+					_
+						-> (True, exp, pState)
+				-> (True, PE_Tuple args, pState)
 where
+	want_pattern_list_t token pState
+		# (expr, pState)
+			= case token of
+				CharListToken charList // To produce a better error message
+					->	charListError charList pState
+				_
+					->	wantPatternT token pState
+		= want_pattern_list_rest expr pState
+
 	want_pattern_list pState
 		# (expr, pState) = wantPattern pState
-		  (token, pState) = nextToken FunctionContext pState
+		= want_pattern_list_rest expr pState
+
+	want_pattern_list_rest expr pState
+		# (token, pState) = nextToken FunctionContext pState
 		| token == CommaToken
 			# (exprs, pState) = want_pattern_list pState
 			= ([expr : exprs], pState)
@@ -3492,19 +3513,38 @@ trySimpleExpressionT SquareOpenToken pState
 	# (list_expr, pState) = wantListExp cIsNotAPattern pState
 	= (True, list_expr, pState)
 trySimpleExpressionT OpenToken pState
-	# (args=:[exp:exps], pState) = want_expression_list pState
-	  pState = wantToken FunctionContext "expression list" CloseToken pState
-	| isEmpty exps
-		= case exp of
-			PE_Ident id
-				-> (True, PE_List [exp], pState)
-			_
-				-> (True, exp, pState)
-		= (True, PE_Tuple args, pState)
+	# (token, pState) = nextToken FunctionContext pState
+	= case token of
+		CloseToken
+			#! unit_cons_ident = predefined_idents.[PD_UnitConsSymbol]
+			-> (True,PE_Ident unit_cons_ident,pState)
+		_
+			# (args=:[exp:exps], pState) = want_expression_list_t token pState
+			  pState = wantToken FunctionContext "expression list" CloseToken pState
+			| isEmpty exps
+				-> case exp of
+					PE_Ident id
+						-> (True, PE_List [exp], pState)
+					_
+						-> (True, exp, pState)
+				-> (True, PE_Tuple args, pState)
 where
+	want_expression_list_t token pState
+		# (expr, pState)
+			= case token of
+				CharListToken charList
+					 // To produce a better error message
+					->	charListError charList pState
+				_
+					-> wantExpressionT token pState
+		= want_expression_list_rest expr pState
+
 	want_expression_list pState
 		# (expr, pState) = wantExpression pState
-		  (token, pState) = nextToken FunctionContext pState
+		= want_expression_list_rest expr pState
+
+	want_expression_list_rest expr pState
+		# (token, pState) = nextToken FunctionContext pState
 		| token == CommaToken
 			# (exprs, pState) = want_expression_list pState
 			= ([expr : exprs], pState)
diff --git a/frontend/predef.dcl b/frontend/predef.dcl
index e649c95..620b470 100644
--- a/frontend/predef.dcl
+++ b/frontend/predef.dcl
@@ -23,7 +23,7 @@ PD_StringTypeIndex :== 0
 PD_Arity2TupleTypeIndex :== 8
 PD_Arity32TupleTypeIndex :== 38
 
-/* identifiers not present the hastable */
+/* identifiers not present the hashtable */
 
 PD_PredefinedModule			:== 0
 
@@ -46,258 +46,264 @@ PD_LazyArrayType			:== 40
 PD_StrictArrayType			:== 41
 PD_UnboxedArrayType			:== 42
 
+PD_UnitType :== 43
+
 // constructors:
 
 FirstConstructorPredefinedSymbolIndex :== PD_ConsSymbol; // to compute index in com_cons_defs
 
-PD_ConsSymbol :== 43
-PD_StrictConsSymbol :== 44
-PD_UnboxedConsSymbol :== 45
-PD_TailStrictConsSymbol :== 46
-PD_StrictTailStrictConsSymbol :== 47
-PD_UnboxedTailStrictConsSymbol :== 48
-PD_OverloadedConsSymbol :== 49
-
-PD_NilSymbol :== 50
-PD_StrictNilSymbol :== 51
-PD_UnboxedNilSymbol :== 52
-PD_TailStrictNilSymbol :== 53
-PD_StrictTailStrictNilSymbol :== 54
-PD_UnboxedTailStrictNilSymbol :== 55
-PD_OverloadedNilSymbol :== 56
-
-PD_Arity2TupleSymbol		:== 57
-PD_Arity32TupleSymbol		:== 87
+PD_ConsSymbol :== 44
+PD_StrictConsSymbol :== 45
+PD_UnboxedConsSymbol :== 46
+PD_TailStrictConsSymbol :== 47
+PD_StrictTailStrictConsSymbol :== 48
+PD_UnboxedTailStrictConsSymbol :== 49
+PD_OverloadedConsSymbol :== 50
+
+PD_NilSymbol :== 51
+PD_StrictNilSymbol :== 52
+PD_UnboxedNilSymbol :== 53
+PD_TailStrictNilSymbol :== 54
+PD_StrictTailStrictNilSymbol :== 55
+PD_UnboxedTailStrictNilSymbol :== 56
+PD_OverloadedNilSymbol :== 57
+
+PD_Arity2TupleSymbol		:== 58
+PD_Arity32TupleSymbol		:== 88
+
+PD_UnitConsSymbol :== 89
 
 // end constructors
 
-PD_TypeVar_a0				:== 88
-PD_TypeVar_a31				:== 119
+PD_TypeVar_a0				:== 90
+PD_TypeVar_a31				:== 121
 
 /* identifiers present in the hashtable */
 
-PD_StdArray					:== 120
-PD_StdEnum					:== 121
-PD_StdBool					:== 122
+PD_StdArray					:== 122
+PD_StdEnum					:== 123
+PD_StdBool					:== 124
 
-PD_AndOp					:== 123
-PD_OrOp						:== 124
+PD_AndOp					:== 125
+PD_OrOp						:== 126
 
 /* Array functions */
 
-PD_ArrayClass				:== 125
+PD_ArrayClass				:== 127
 
-PD_CreateArrayFun			:== 126
-PD__CreateArrayFun			:== 127
-PD_ArraySelectFun			:== 128
-PD_UnqArraySelectFun		:== 129
-PD_ArrayUpdateFun			:== 130
-PD_ArrayReplaceFun			:== 131
-PD_ArraySizeFun				:== 132
-PD_UnqArraySizeFun			:== 133
+PD_CreateArrayFun			:== 128
+PD__CreateArrayFun			:== 129
+PD_ArraySelectFun			:== 130
+PD_UnqArraySelectFun		:== 131
+PD_ArrayUpdateFun			:== 132
+PD_ArrayReplaceFun			:== 133
+PD_ArraySizeFun				:== 134
+PD_UnqArraySizeFun			:== 135
 
 /* Enum/Comprehension functions */
 
-PD_SmallerFun				:== 134
-PD_LessOrEqualFun			:== 135
-PD_IncFun					:== 136
-PD_SubFun					:== 137
-PD_From						:== 138
-PD_FromThen					:== 139
-PD_FromTo					:== 140
-PD_FromThenTo				:== 141
+PD_SmallerFun				:== 136
+PD_LessOrEqualFun			:== 137
+PD_IncFun					:== 138
+PD_SubFun					:== 139
+PD_From						:== 140
+PD_FromThen					:== 141
+PD_FromTo					:== 142
+PD_FromThenTo				:== 143
 
 /* StdMisc */
-PD_StdMisc					:== 142
-PD_abort					:== 143
-PD_undef					:== 144
+PD_StdMisc					:== 144
+PD_abort					:== 145
+PD_undef					:== 146
 
-PD_Start					:== 145
+PD_Start					:== 147
 
-PD_DummyForStrictAliasFun	:== 146
+PD_DummyForStrictAliasFun	:== 148
 
-PD_StdStrictLists:==147
+PD_StdStrictLists:==149
 
-PD_cons:==148
-PD_decons:==149
+PD_cons:==150
+PD_decons:==151
 
-PD_cons_u:==150
-PD_decons_u:==151
+PD_cons_u:==152
+PD_decons_u:==153
 
-PD_cons_uts:==152
-PD_decons_uts:==153
+PD_cons_uts:==154
+PD_decons_uts:==155
 
-PD_nil:==154
-PD_nil_u:==155
-PD_nil_uts:==156
+PD_nil:==156
+PD_nil_u:==157
+PD_nil_uts:==158
 
-PD_ListClass :== 157
-PD_UListClass :== 158
-PD_UTSListClass :== 159
+PD_ListClass :== 159
+PD_UListClass :== 160
+PD_UTSListClass :== 161
 
 /* Dynamics */
 
 // TC class
-PD_TypeCodeMember			:== 160
-PD_TypeCodeClass			:== 161
+PD_TypeCodeMember			:== 162
+PD_TypeCodeClass			:== 163
 // dynamic module
-PD_StdDynamic				:== 162
+PD_StdDynamic				:== 164
 // dynamic type
-PD_Dyn_DynamicTemp				:== 163
+PD_Dyn_DynamicTemp				:== 165
 // type code (type)
-PD_Dyn_TypeCode					:== 164
+PD_Dyn_TypeCode					:== 166
 // unification (type)
-PD_Dyn_UnificationEnvironment	:== 165
+PD_Dyn_UnificationEnvironment	:== 167
 // type code (expressions)
-PD_Dyn_TypeScheme			:== 166
-PD_Dyn_TypeApp				:== 167
-PD_Dyn_TypeVar				:== 168
-PD_Dyn_TypeCons				:== 169
-PD_Dyn_TypeUnique			:== 170
-PD_Dyn__TypeFixedVar		:== 171
+PD_Dyn_TypeScheme			:== 168
+PD_Dyn_TypeApp				:== 169
+PD_Dyn_TypeVar				:== 170
+PD_Dyn_TypeCons				:== 171
+PD_Dyn_TypeUnique			:== 172
+PD_Dyn__TypeFixedVar		:== 173
 // unification (expressions)
-PD_Dyn_initial_unification_environment	:== 172
-PD_Dyn_bind_global_type_pattern_var		:== 173
-PD_Dyn_unify							:== 174
-PD_Dyn_normalise						:== 175
+PD_Dyn_initial_unification_environment	:== 174
+PD_Dyn_bind_global_type_pattern_var		:== 175
+PD_Dyn_unify							:== 176
+PD_Dyn_normalise						:== 177
 
 /* Generics */
-PD_StdGeneric				:== 176
+PD_StdGeneric				:== 178
 // Generics types
-PD_TypeBimap				:== 177
-PD_TypeUNIT					:== 178
-PD_TypeEITHER				:== 179
-PD_TypePAIR					:== 180
+PD_TypeBimap				:== 179
+PD_TypeUNIT					:== 180
+PD_TypeEITHER				:== 181
+PD_TypePAIR					:== 182
 // for constructor info
-PD_TypeCONS					:== 181
-PD_TypeRECORD				:== 182
-PD_TypeFIELD				:== 183
-PD_TypeOBJECT				:== 184
-PD_TGenericConsDescriptor	:== 185
-PD_TGenericRecordDescriptor	:== 186
-PD_TGenericFieldDescriptor 	:== 187
-PD_TGenericTypeDefDescriptor :== 188
-PD_TGenConsPrio				:== 189
-PD_TGenConsAssoc			:== 190
-PD_TGenType					:== 191
-
-PD_TypeGenericDict 			:== 192
+PD_TypeCONS					:== 183
+PD_TypeRECORD				:== 184
+PD_TypeFIELD				:== 185
+PD_TypeOBJECT				:== 186
+PD_TGenericConsDescriptor	:== 187
+PD_TGenericRecordDescriptor	:== 188
+PD_TGenericFieldDescriptor 	:== 189
+PD_TGenericTypeDefDescriptor :== 190
+PD_TGenConsPrio				:== 191
+PD_TGenConsAssoc			:== 192
+PD_TGenType					:== 193
+
+PD_TypeGenericDict 			:== 194
 // Generics fields
-PD_map_to					:== 193
-PD_map_from					:== 194
+PD_map_to					:== 195
+PD_map_from					:== 196
 // Generics expression
-PD_ConsBimap				:== 195
-PD_ConsUNIT					:== 196
-PD_ConsLEFT					:== 197
-PD_ConsRIGHT				:== 198
-PD_ConsPAIR					:== 199
+PD_ConsBimap				:== 197
+PD_ConsUNIT					:== 198
+PD_ConsLEFT					:== 199
+PD_ConsRIGHT				:== 200
+PD_ConsPAIR					:== 201
 // for constructor info
-PD_ConsCONS					:== 200
-PD_ConsRECORD				:== 201
-PD_ConsFIELD				:== 202
-PD_ConsOBJECT				:== 203
-PD_CGenericConsDescriptor 	:== 204
-PD_CGenericRecordDescriptor	:== 205
-PD_CGenericFieldDescriptor 	:== 206
-PD_CGenericTypeDefDescriptor :== 207
-PD_CGenConsNoPrio			:== 208
-PD_CGenConsPrio				:== 209
-PD_CGenConsAssocNone		:== 210
-PD_CGenConsAssocLeft		:== 211
-PD_CGenConsAssocRight		:== 212
-PD_CGenTypeCons				:== 213
-PD_CGenTypeVar				:== 214
-PD_CGenTypeArrow			:== 215
-PD_CGenTypeApp				:== 216
-
-PD_bimapId					:== 217
-PD_GenericBimap				:== 218
-
-PD_FromS					:== 219
-PD_FromTS					:== 220
-PD_FromSTS					:== 221
-PD_FromU					:== 222
-PD_FromUTS					:== 223
-PD_FromO					:== 224
-
-PD_FromThenS				:== 225
-PD_FromThenTS				:== 226
-PD_FromThenSTS				:== 227
-PD_FromThenU				:== 228
-PD_FromThenUTS				:== 229
-PD_FromThenO				:== 230
-
-PD_FromToS					:== 231
-PD_FromToTS					:== 232
-PD_FromToSTS				:== 233
-PD_FromToU					:== 234
-PD_FromToUTS				:== 235
-PD_FromToO					:== 236
-
-PD_FromThenToS				:== 237
-PD_FromThenToTS				:== 238
-PD_FromThenToSTS			:== 239
-PD_FromThenToU				:== 240
-PD_FromThenToUTS			:== 241
-PD_FromThenToO				:== 242
-
-PD_Dyn__to_TypeCodeConstructor	:== 243
-PD_TypeCodeConstructor :== 244
-
-PD_TC_Int			:== 245
-PD_TC_Char			:== 246
-PD_TC_Real			:== 247
-PD_TC_Bool			:== 248
-PD_TC_Dynamic		:== 249
-PD_TC_File			:== 250
-PD_TC_World			:== 251
-
-PD_TC__Arrow		:== 252
-
-PD_TC__List			:== 253
-PD_TC__StrictList	:== 254
-PD_TC__UnboxedList	:== 255
-PD_TC__TailStrictList	:== 256
-PD_TC__StrictTailStrictList	:== 257
-PD_TC__UnboxedTailStrictList	:== 258
-
-PD_TC__Tuple2		:== 259
-PD_TC__Tuple3		:== 260
-PD_TC__Tuple4		:== 261
-PD_TC__Tuple5		:== 262
-PD_TC__Tuple6		:== 263
-PD_TC__Tuple7		:== 264
-PD_TC__Tuple8		:== 265
-PD_TC__Tuple9		:== 266
-PD_TC__Tuple10		:== 267
-PD_TC__Tuple11		:== 268
-PD_TC__Tuple12		:== 269
-PD_TC__Tuple13		:== 270
-PD_TC__Tuple14		:== 271
-PD_TC__Tuple15		:== 272
-PD_TC__Tuple16		:== 273
-PD_TC__Tuple17		:== 274
-PD_TC__Tuple18		:== 275
-PD_TC__Tuple19		:== 276
-PD_TC__Tuple20		:== 277
-PD_TC__Tuple21		:== 278
-PD_TC__Tuple22		:== 279
-PD_TC__Tuple23		:== 280
-PD_TC__Tuple24		:== 281
-PD_TC__Tuple25		:== 282
-PD_TC__Tuple26		:== 283
-PD_TC__Tuple27		:== 284
-PD_TC__Tuple28		:== 285
-PD_TC__Tuple29		:== 286
-PD_TC__Tuple30		:== 287
-PD_TC__Tuple31		:== 288
-PD_TC__Tuple32		:== 289
-
-PD_TC__LazyArray	:== 290
-PD_TC__StrictArray	:== 291
-PD_TC__UnboxedArray	:== 292
-
-PD_NrOfPredefSymbols		:== 293
+PD_ConsCONS					:== 202
+PD_ConsRECORD				:== 203
+PD_ConsFIELD				:== 204
+PD_ConsOBJECT				:== 205
+PD_CGenericConsDescriptor 	:== 206
+PD_CGenericRecordDescriptor	:== 207
+PD_CGenericFieldDescriptor 	:== 208
+PD_CGenericTypeDefDescriptor :== 209
+PD_CGenConsNoPrio			:== 210
+PD_CGenConsPrio				:== 211
+PD_CGenConsAssocNone		:== 212
+PD_CGenConsAssocLeft		:== 213
+PD_CGenConsAssocRight		:== 214
+PD_CGenTypeCons				:== 215
+PD_CGenTypeVar				:== 216
+PD_CGenTypeArrow			:== 217
+PD_CGenTypeApp				:== 218
+
+PD_bimapId					:== 219
+PD_GenericBimap				:== 220
+
+PD_FromS					:== 221
+PD_FromTS					:== 222
+PD_FromSTS					:== 223
+PD_FromU					:== 224
+PD_FromUTS					:== 225
+PD_FromO					:== 226
+
+PD_FromThenS				:== 227
+PD_FromThenTS				:== 228
+PD_FromThenSTS				:== 229
+PD_FromThenU				:== 230
+PD_FromThenUTS				:== 231
+PD_FromThenO				:== 232
+
+PD_FromToS					:== 233
+PD_FromToTS					:== 234
+PD_FromToSTS				:== 235
+PD_FromToU					:== 236
+PD_FromToUTS				:== 237
+PD_FromToO					:== 238
+
+PD_FromThenToS				:== 239
+PD_FromThenToTS				:== 240
+PD_FromThenToSTS			:== 241
+PD_FromThenToU				:== 242
+PD_FromThenToUTS			:== 243
+PD_FromThenToO				:== 244
+
+PD_Dyn__to_TypeCodeConstructor	:== 245
+PD_TypeCodeConstructor :== 246
+
+PD_TC_Int			:== 247
+PD_TC_Char			:== 248
+PD_TC_Real			:== 249
+PD_TC_Bool			:== 250
+PD_TC_Dynamic		:== 251
+PD_TC_File			:== 252
+PD_TC_World			:== 253
+
+PD_TC__Arrow		:== 254
+
+PD_TC__List			:== 255
+PD_TC__StrictList	:== 256
+PD_TC__UnboxedList	:== 257
+PD_TC__TailStrictList	:== 258
+PD_TC__StrictTailStrictList	:== 259
+PD_TC__UnboxedTailStrictList	:== 260
+
+PD_TC__Tuple2		:== 261
+PD_TC__Tuple3		:== 262
+PD_TC__Tuple4		:== 263
+PD_TC__Tuple5		:== 264
+PD_TC__Tuple6		:== 265
+PD_TC__Tuple7		:== 266
+PD_TC__Tuple8		:== 267
+PD_TC__Tuple9		:== 268
+PD_TC__Tuple10		:== 269
+PD_TC__Tuple11		:== 270
+PD_TC__Tuple12		:== 271
+PD_TC__Tuple13		:== 272
+PD_TC__Tuple14		:== 273
+PD_TC__Tuple15		:== 274
+PD_TC__Tuple16		:== 275
+PD_TC__Tuple17		:== 276
+PD_TC__Tuple18		:== 277
+PD_TC__Tuple19		:== 278
+PD_TC__Tuple20		:== 279
+PD_TC__Tuple21		:== 280
+PD_TC__Tuple22		:== 281
+PD_TC__Tuple23		:== 282
+PD_TC__Tuple24		:== 283
+PD_TC__Tuple25		:== 284
+PD_TC__Tuple26		:== 285
+PD_TC__Tuple27		:== 286
+PD_TC__Tuple28		:== 287
+PD_TC__Tuple29		:== 288
+PD_TC__Tuple30		:== 289
+PD_TC__Tuple31		:== 290
+PD_TC__Tuple32		:== 291
+
+PD_TC__LazyArray	:== 292
+PD_TC__StrictArray	:== 293
+PD_TC__UnboxedArray	:== 294
+
+PD_TC__Unit			:== 295
+
+PD_NrOfPredefSymbols		:== 296
 
 GetTupleConsIndex tup_arity :== PD_Arity2TupleSymbol + tup_arity - 2
 GetTupleTypeIndex tup_arity :== PD_Arity2TupleType + tup_arity - 2
diff --git a/frontend/predef.icl b/frontend/predef.icl
index 8157dfd..c21a608 100644
--- a/frontend/predef.icl
+++ b/frontend/predef.icl
@@ -33,7 +33,8 @@ predefined_idents
 					[PD_StrictTailStrictNilSymbol] = i "_!Nil!",
 					[PD_UnboxedTailStrictNilSymbol] = i "_#Nil!",
 					[PD_OverloadedNilSymbol] = i "_|Nil",
-			
+					[PD_UnitConsSymbol] = i "_Unit",
+
 					[PD_PredefinedModule] = i "_predefined",
 					[PD_StringType] = i "_String",
 					[PD_ListType] = i PD_ListType_String,
@@ -46,6 +47,7 @@ predefined_idents
 					[PD_LazyArrayType] = i "_Array",
 					[PD_StrictArrayType] = i "_!Array",
 					[PD_UnboxedArrayType] = i PD_UnboxedArray_String,
+					[PD_UnitType] = i "_Unit",
 					[PD_TypeCodeMember] = i "_type_code",
 					[PD_DummyForStrictAliasFun] = i "_dummyForStrictAlias"
 				}
@@ -168,6 +170,8 @@ predefined_idents
 					[PD_TC__StrictArray] = i "TC__StrictArray",
 					[PD_TC__UnboxedArray] = i "TC__UnboxedArray",
 
+					[PD_TC__Unit] = i "TC__Unit",
+
 					[PD_StdGeneric] = i "StdGeneric",
 					[PD_TypeBimap] = i "Bimap",
 					[PD_ConsBimap] = i "_Bimap",
@@ -309,6 +313,7 @@ where
 			<<= (local_predefined_idents, PD_LazyArrayType)
 			<<= (local_predefined_idents, PD_StrictArrayType)
 			<<= (local_predefined_idents, PD_UnboxedArrayType)
+			<<= (local_predefined_idents, PD_UnitType) <<= (local_predefined_idents, PD_UnitConsSymbol)
 			<<= (local_predefined_idents, PD_TypeCodeMember)
 			<<= (local_predefined_idents, PD_DummyForStrictAliasFun) // MW++
 	where
@@ -369,7 +374,7 @@ where
 					<<- (local_predefined_idents,	IC_Type, PD_TypeCodeConstructor)
 
 					<<- (local_predefined_idents,	IC_Module NoQualifiedIdents, PD_StdGeneric)
-		# hash_table = put_predefined_idents_in_hash_table PD_TC_Int PD_TC__UnboxedArray IC_Expression local_predefined_idents hash_table
+		# hash_table = put_predefined_idents_in_hash_table PD_TC_Int PD_TC__Unit IC_Expression local_predefined_idents hash_table
 
 		# hash_table = put_predefined_idents_in_hash_table PD_TypeBimap PD_TypeGenericDict IC_Type local_predefined_idents hash_table
 		# hash_table = put_predefined_idents_in_hash_table PD_ConsBimap PD_bimapId IC_Expression local_predefined_idents hash_table
@@ -421,6 +426,15 @@ make_list_definition list_type_pre_def_symbol_index cons_pre_def_symbol_index ni
 	  				pc_cons_prio =  NoPrio, pc_exi_vars = [], pc_cons_pos = PreDefPos pre_mod_id}
 	= (list_def,ParsedConstructorToConsDef cons_def,ParsedConstructorToConsDef nil_def,pre_def_symbols);
 
+make_unit_definition :: Ident *{#PredefinedSymbol} -> (!TypeDef TypeRhs,!ConsDef,!.{#PredefinedSymbol})
+make_unit_definition pre_mod_id pre_def_symbols
+	# unit_cons_ident = predefined_idents.[PD_UnitConsSymbol]
+	  unit_cons_symb = {ds_ident = unit_cons_ident, ds_arity=0 ,ds_index = PD_UnitConsSymbol-FirstConstructorPredefinedSymbolIndex}
+	  (unit_type_def, pre_def_symbols) = make_type_def PD_UnitType [] (AlgType [unit_cons_symb]) pre_def_symbols	
+	  unit_cons_def = {pc_cons_ident = unit_cons_ident, pc_cons_arity = 0, pc_arg_types = [], pc_args_strictness=NotStrict, pc_context = [],
+		  			   pc_cons_prio =  NoPrio, pc_exi_vars = [], pc_cons_pos = PreDefPos pre_mod_id}
+	= (unit_type_def,ParsedConstructorToConsDef unit_cons_def,pre_def_symbols);
+
 buildPredefinedModule :: !Bool !*PredefinedSymbols -> (!ScannedModule, !.PredefinedSymbols)
 buildPredefinedModule support_dynamics pre_def_symbols 
 	# type_var_ident = predefined_idents.[PD_TypeVar_a0]
@@ -454,7 +468,11 @@ buildPredefinedModule support_dynamics pre_def_symbols
 	  (strict_def, pre_def_symbols)		= make_type_def PD_StrictArrayType [type_var] (AbstractType cAllBitsClear) pre_def_symbols
 	  (unboxed_def, pre_def_symbols)	= make_type_def PD_UnboxedArrayType [type_var] (AbstractType cAllBitsClear) pre_def_symbols
 
-	  (type_defs, cons_defs, pre_def_symbols)	= add_tuple_defs pre_mod_ident MaxTupleArity [array_def,strict_def,unboxed_def] [] pre_def_symbols
+	  (unit_type_def,unit_cons_def,pre_def_symbols) = make_unit_definition pre_mod_ident pre_def_symbols
+
+	  array_and_unit_type_defs = [array_def,strict_def,unboxed_def,unit_type_def]
+	  (type_defs, cons_defs, pre_def_symbols)	= add_tuple_defs pre_mod_ident MaxTupleArity array_and_unit_type_defs [unit_cons_def] pre_def_symbols
+
 	  alias_dummy_type = make_identity_fun_type alias_dummy_ident type_var
 	  (def_classes, def_members) = make_predefined_classes_and_members support_dynamics 
 	= ({ mod_ident = pre_mod_ident, mod_modification_time = "", mod_type = MK_System, mod_imports = [],mod_foreign_exports=[], mod_imported_objects = [],