From bac5cdde01c4f25315daa74ea234b8780f66a2c9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=89tienne=20Reuh=20Fildadut?= <fildadut@reuh.eu>
Date: Fri, 9 Sep 2022 14:54:45 +0900
Subject: [PATCH] Change equality test to reference comparison for mutable
 values

---
 LANGUAGE.md                       |  37 +++++++-
 interpreter/common.lua            |  63 ++++++++----
 stdlib/types.lua                  |  16 +++-
 test/tests/equality operator.ans  |  28 ++++--
 test/tests/equality operator.lua  | 153 +++++++++++++++++++-----------
 test/tests/object comparaison.ans |  23 +++++
 test/tests/object comparaison.lua |  78 +++++++++++++++
 test/tests/object constructor.lua |   4 +-
 8 files changed, 315 insertions(+), 87 deletions(-)
 create mode 100644 test/tests/object comparaison.ans
 create mode 100644 test/tests/object comparaison.lua

diff --git a/LANGUAGE.md b/LANGUAGE.md
index 48bfe75..2c52a26 100644
--- a/LANGUAGE.md
+++ b/LANGUAGE.md
@@ -682,6 +682,39 @@ These can be used to represent some caracters in string and other text elements
 
 Only `0` and `nil` are false. Everything else is considered true.
 
+#### Equality
+
+Anselme consider two objects to be equal if they can *always* be used interchangeably.
+
+In practice, this results in two main cases for equality tests:
+
+* immutable values (strings, numbers, constants, ...). They are compared by recursively making sure all of their values and structure are equal.
+
+```
+(All of the following if true)
+~ 5 == 5
+~ "foo" == "foo"
+~ constant([1,2,3]) == constant([1,2,3])
+```
+
+* mutable values (list, map, objects that are not constant). They are compared by reference, i.e. they are only considered equal if they are not distinct objects, even if they contain the same values and structure.
+
+```
+:a = [1,2,3]
+:b = a
+:c = [1,2,3]
+
+(True:)
+~ a == b
+
+(False:)
+~ a == c
+
+(a and c are not interchangeable as they are two distinct lists; if we do:)
+~ a(1) = 42
+(This will change the first value of both a and b, but not c.)
+```
+
 #### Refering to an identifier
 
 Any defined identifier can be accessed from an expression by using its name; the identifier will be first searched in the current namespace, then go up until it finds it as described in [identifiers](#identifiers).
@@ -930,9 +963,9 @@ Built-in operators:
 
 ##### Comparaison
 
-`a == b`: returns `1` if a and b have the same value (will recursively compare list and pairs), `0` otherwise
+`a == b`: returns `1` if a and b are considered equal, `0` otherwise
 
-`a != b`: returns `1` if a and b do not have the same value, `0` otherwise
+`a != b`: returns `1` if a and b are not equal, `0` otherwise
 
 These only work on numbers:
 
diff --git a/interpreter/common.lua b/interpreter/common.lua
index 64806e0..1c683c5 100644
--- a/interpreter/common.lua
+++ b/interpreter/common.lua
@@ -150,10 +150,17 @@ common = {
 	get_variable = function(state, fqm)
 		local var = state.variables[fqm]
 		if var.type == "pending definition" then
+			-- evaluate
 			local v, e = eval(state, var.value.expression)
 			if not v then
 				return nil, ("%s; while evaluating default value for variable %q defined at %s"):format(e, fqm, var.value.source)
 			end
+			-- make constant if variable is constant
+			if state.variable_constants[fqm] then
+				v = copy(v)
+				common.mark_constant(v)
+			end
+			-- set variable
 			local s, err = common.set_variable(state, fqm, v, state.variable_constants[fqm])
 			if not s then return nil, err end
 			return v
@@ -164,13 +171,10 @@ common = {
 	--- set the value of a variable
 	-- returns true
 	-- returns nil, err
-	set_variable = function(state, name, val, defining_a_constant)
+	set_variable = function(state, name, val, bypass_constant_check)
 		if val.type ~= "pending definition" then
 			-- check constant
-			if defining_a_constant then
-				val = copy(val)
-				common.mark_constant(val)
-			else
+			if not bypass_constant_check then
 				local s, e = common.check_mutable(state, name)
 				if not s then
 					return nil, ("%s; while assigning value to variable %q"):format(e, name)
@@ -270,23 +274,15 @@ common = {
 			return true
 		end
 	end,
-	--- compare two anselme value for equality
+	--- compare two anselme values for equality.
+	-- for immutable values or constants: compare by value
+	-- for mutable values: compare by reference
 	compare = function(a, b)
-		if a.type ~= b.type then
+		if a.type ~= b.type or a.constant ~= b.constant then
 			return false
 		end
 		if a.type == "pair" or a.type == "annotated" then
 			return common.compare(a.value[1], b.value[1]) and common.compare(a.value[2], b.value[2])
-		elseif a.type == "list" then
-			if #a.value ~= #b.value then
-				return false
-			end
-			for i, v in ipairs(a.value) do
-				if not common.compare(v, b.value[i]) then
-					return false
-				end
-			end
-			return true
 		elseif a.type == "function reference" then
 			if #a.value ~= #b.value then
 				return false
@@ -304,6 +300,39 @@ common = {
 				end
 			end
 			return true
+		-- mutable types: need to be constant
+		elseif a.constant and a.type == "list" then
+			if #a.value ~= #b.value then
+				return false
+			end
+			for i, v in ipairs(a.value) do
+				if not common.compare(v, b.value[i]) then
+					return false
+				end
+			end
+			return true
+		elseif a.constant and a.type == "object" then
+			if a.value.class ~= b.value.class then
+				return false
+			end
+			-- check every attribute redefined in a and b
+			-- NOTE: comparaison will fail if an attribute has been redefined in only one of the object, even if it was set to the same value as the original class attribute
+			local compared = {}
+			for name, v in pairs(a.value.attributes) do
+				compared[name] = true
+				if not b.value.attributes[name] or not common.compare(v, b.value.attributes[name]) then
+					return false
+				end
+			end
+			for name, v in pairs(b.value.attributes) do
+				if not compared[name] then
+					if not a.value.attributes[name] or not common.compare(v, a.value.attributes[name]) then
+						return false
+					end
+				end
+			end
+			return true
+		-- the rest
 		else
 			return a.value == b.value
 		end
diff --git a/stdlib/types.lua b/stdlib/types.lua
index 944d6f8..f4cc466 100644
--- a/stdlib/types.lua
+++ b/stdlib/types.lua
@@ -1,4 +1,4 @@
-local format, to_lua, from_lua, events, anselme
+local format, to_lua, from_lua, events, anselme, escape
 
 local types = {}
 types.lua = {
@@ -99,8 +99,7 @@ types.anselme = {
 		end,
 		to_lua = function(val)
 			local l = {}
-			-- handle non-pair before pairs as LuaJIT's table.insert
-			-- will always insert after the last element even if there are some nil before unlike PUC
+			-- handle non-pair before pairs as LuaJIT's table.insert will always insert after the last element even if there are some nil before unlike PUC
 			for _, v in ipairs(val) do
 				if v.type ~= "pair" then
 					local s, e = to_lua(v)
@@ -168,7 +167,15 @@ types.anselme = {
 	},
 	object = {
 		format = function(val)
-			return ("%%%s"):format(val.class)
+			local attributes = {}
+			for name, v in pairs(val.attributes) do
+				table.insert(attributes, ("%s=%s"):format(name:gsub("^"..escape(val.class)..".", ""), format(v)))
+			end
+			if #attributes > 0 then
+				return ("%%%s(%s)"):format(val.class, table.concat(attributes, ", "))
+			else
+				return ("%%%s"):format(val.class)
+			end
 		end,
 		to_lua = nil
 	},
@@ -186,5 +193,6 @@ package.loaded[...] = types
 local common = require((...):gsub("stdlib%.types$", "interpreter.common"))
 format, to_lua, from_lua, events = common.format, common.to_lua, common.from_lua, common.events
 anselme = require((...):gsub("stdlib%.types$", "anselme"))
+escape = require((...):gsub("stdlib%.types$", "parser.common")).escape
 
 return types
diff --git a/test/tests/equality operator.ans b/test/tests/equality operator.ans
index 4cc418f..30f746a 100644
--- a/test/tests/equality operator.ans	
+++ b/test/tests/equality operator.ans	
@@ -1,19 +1,29 @@
-:a = [1=2]
+::a = [1=2]
 
-0 = {a == [5=2]}
+0 = {a == [5=2]!constant}
 
-0 = {a == [1=3]}
+0 = {a == [1=3]!constant}
 
-1 = {a == [1=2]}
+1 = {a == [1=2]!constant}
 
-:b = [1,2,3]
+::b = [1,2,3]
 
 0 = {b == a}
 
-0 = {b == []}
+0 = {b == []!constant}
 
-0 = {b == [3,1,2]}
+0 = {b == [3,1,2]!constant}
 
-0 = {b == [1,2,3,4]}
+0 = {b == [1,2,3,4]!constant}
 
-1 = {b == [1,2,3]}
+1 = {b == [1,2,3]!constant}
+
+:c = [1,2,3]
+
+0 = {c == b}
+
+1 = {c!constant == b}
+
+::d = [1,2,3]
+
+1 = {d == b}
diff --git a/test/tests/equality operator.lua b/test/tests/equality operator.lua
index de9c43d..17f5f10 100644
--- a/test/tests/equality operator.lua	
+++ b/test/tests/equality operator.lua	
@@ -1,101 +1,148 @@
 local _={}
-_[41]={}
-_[40]={}
-_[39]={}
-_[38]={}
-_[37]={}
-_[36]={}
-_[35]={}
-_[34]={}
-_[33]={tags=_[41],text="1"}
-_[32]={tags=_[41],text="1 = "}
-_[31]={tags=_[40],text="0"}
-_[30]={tags=_[40],text="0 = "}
-_[29]={tags=_[39],text="0"}
-_[28]={tags=_[39],text="0 = "}
-_[27]={tags=_[38],text="0"}
-_[26]={tags=_[38],text="0 = "}
-_[25]={tags=_[37],text="0"}
-_[24]={tags=_[37],text="0 = "}
-_[23]={tags=_[36],text="1"}
-_[22]={tags=_[36],text="1 = "}
-_[21]={tags=_[35],text="0"}
-_[20]={tags=_[35],text="0 = "}
-_[19]={tags=_[34],text="0"}
-_[18]={tags=_[34],text="0 = "}
+_[67]={}
+_[66]={}
+_[65]={}
+_[64]={}
+_[63]={}
+_[62]={}
+_[61]={}
+_[60]={}
+_[59]={}
+_[58]={}
+_[57]={}
+_[56]={}
+_[55]={}
+_[54]={}
+_[53]={}
+_[52]={}
+_[51]={}
+_[50]={}
+_[49]={}
+_[48]={}
+_[47]={}
+_[46]={}
+_[45]={tags=_[67],text="1"}
+_[44]={tags=_[66],text="1 = "}
+_[43]={tags=_[65],text="1"}
+_[42]={tags=_[64],text="1 = "}
+_[41]={tags=_[63],text="0"}
+_[40]={tags=_[62],text="0 = "}
+_[39]={tags=_[61],text="1"}
+_[38]={tags=_[60],text="1 = "}
+_[37]={tags=_[59],text="0"}
+_[36]={tags=_[58],text="0 = "}
+_[35]={tags=_[57],text="0"}
+_[34]={tags=_[56],text="0 = "}
+_[33]={tags=_[55],text="0"}
+_[32]={tags=_[54],text="0 = "}
+_[31]={tags=_[53],text="0"}
+_[30]={tags=_[52],text="0 = "}
+_[29]={tags=_[51],text="1"}
+_[28]={tags=_[50],text="1 = "}
+_[27]={tags=_[49],text="0"}
+_[26]={tags=_[48],text="0 = "}
+_[25]={tags=_[47],text="0"}
+_[24]={tags=_[46],text="0 = "}
+_[23]={_[44],_[45]}
+_[22]={_[42],_[43]}
+_[21]={_[40],_[41]}
+_[20]={_[38],_[39]}
+_[19]={_[36],_[37]}
+_[18]={_[34],_[35]}
 _[17]={_[32],_[33]}
 _[16]={_[30],_[31]}
 _[15]={_[28],_[29]}
 _[14]={_[26],_[27]}
 _[13]={_[24],_[25]}
-_[12]={_[22],_[23]}
-_[11]={_[20],_[21]}
-_[10]={_[18],_[19]}
-_[9]={"return"}
-_[8]={"text",_[17]}
-_[7]={"text",_[16]}
-_[6]={"text",_[15]}
-_[5]={"text",_[14]}
-_[4]={"text",_[13]}
-_[3]={"text",_[12]}
-_[2]={"text",_[11]}
-_[1]={"text",_[10]}
-return {_[1],_[2],_[3],_[4],_[5],_[6],_[7],_[8],_[9]}
+_[12]={"return"}
+_[11]={"text",_[23]}
+_[10]={"text",_[22]}
+_[9]={"text",_[21]}
+_[8]={"text",_[20]}
+_[7]={"text",_[19]}
+_[6]={"text",_[18]}
+_[5]={"text",_[17]}
+_[4]={"text",_[16]}
+_[3]={"text",_[15]}
+_[2]={"text",_[14]}
+_[1]={"text",_[13]}
+return {_[1],_[2],_[3],_[4],_[5],_[6],_[7],_[8],_[9],_[10],_[11],_[12]}
 --[[
 { "text", { {
-      tags = <1>{},
+      tags = {},
       text = "0 = "
     }, {
-      tags = <table 1>,
+      tags = {},
       text = "0"
     } } }
 { "text", { {
-      tags = <1>{},
+      tags = {},
       text = "0 = "
     }, {
-      tags = <table 1>,
+      tags = {},
       text = "0"
     } } }
 { "text", { {
-      tags = <1>{},
+      tags = {},
       text = "1 = "
     }, {
-      tags = <table 1>,
+      tags = {},
       text = "1"
     } } }
 { "text", { {
-      tags = <1>{},
+      tags = {},
       text = "0 = "
     }, {
-      tags = <table 1>,
+      tags = {},
       text = "0"
     } } }
 { "text", { {
-      tags = <1>{},
+      tags = {},
       text = "0 = "
     }, {
-      tags = <table 1>,
+      tags = {},
       text = "0"
     } } }
 { "text", { {
-      tags = <1>{},
+      tags = {},
       text = "0 = "
     }, {
-      tags = <table 1>,
+      tags = {},
       text = "0"
     } } }
 { "text", { {
-      tags = <1>{},
+      tags = {},
       text = "0 = "
     }, {
-      tags = <table 1>,
+      tags = {},
       text = "0"
     } } }
 { "text", { {
-      tags = <1>{},
+      tags = {},
       text = "1 = "
     }, {
-      tags = <table 1>,
+      tags = {},
+      text = "1"
+    } } }
+{ "text", { {
+      tags = {},
+      text = "0 = "
+    }, {
+      tags = {},
+      text = "0"
+    } } }
+{ "text", { {
+      tags = {},
+      text = "1 = "
+    }, {
+      tags = {},
+      text = "1"
+    } } }
+{ "text", { {
+      tags = {},
+      text = "1 = "
+    }, {
+      tags = {},
       text = "1"
     } } }
 { "return" }
diff --git a/test/tests/object comparaison.ans b/test/tests/object comparaison.ans
new file mode 100644
index 0000000..af40f6e
--- /dev/null
+++ b/test/tests/object comparaison.ans	
@@ -0,0 +1,23 @@
+% class
+	:a:b = "foo"
+	:c = "bar"
+
+:o = class
+:a = class
+::b = class
+
+0 = {o == a}
+0 = {o == b}
+1 = {o!constant == b}
+
+~ o.b := "haha"
+
+0 = {o!constant == b}
+
+~ a.b := "haha"
+
+1 = {o!constant == a!constant}
+
+~ o.b := "foo"
+
+0 = {o!constant == b}
diff --git a/test/tests/object comparaison.lua b/test/tests/object comparaison.lua
new file mode 100644
index 0000000..94b32f7
--- /dev/null
+++ b/test/tests/object comparaison.lua	
@@ -0,0 +1,78 @@
+local _={}
+_[33]={}
+_[32]={}
+_[31]={}
+_[30]={}
+_[29]={}
+_[28]={}
+_[27]={}
+_[26]={}
+_[25]={}
+_[24]={}
+_[23]={}
+_[22]={}
+_[21]={tags=_[33],text="0"}
+_[20]={tags=_[32],text="0 = "}
+_[19]={tags=_[31],text="1"}
+_[18]={tags=_[30],text="1 = "}
+_[17]={tags=_[29],text="0"}
+_[16]={tags=_[28],text="0 = "}
+_[15]={tags=_[27],text="1"}
+_[14]={tags=_[26],text="1 = "}
+_[13]={tags=_[25],text="0"}
+_[12]={tags=_[24],text="0 = "}
+_[11]={tags=_[23],text="0"}
+_[10]={tags=_[22],text="0 = "}
+_[9]={_[20],_[21]}
+_[8]={_[18],_[19]}
+_[7]={_[16],_[17]}
+_[6]={_[10],_[11],_[12],_[13],_[14],_[15]}
+_[5]={"return"}
+_[4]={"text",_[9]}
+_[3]={"text",_[8]}
+_[2]={"text",_[7]}
+_[1]={"text",_[6]}
+return {_[1],_[2],_[3],_[4],_[5]}
+--[[
+{ "text", { {
+      tags = {},
+      text = "0 = "
+    }, {
+      tags = {},
+      text = "0"
+    }, {
+      tags = {},
+      text = "0 = "
+    }, {
+      tags = {},
+      text = "0"
+    }, {
+      tags = {},
+      text = "1 = "
+    }, {
+      tags = {},
+      text = "1"
+    } } }
+{ "text", { {
+      tags = {},
+      text = "0 = "
+    }, {
+      tags = {},
+      text = "0"
+    } } }
+{ "text", { {
+      tags = {},
+      text = "1 = "
+    }, {
+      tags = {},
+      text = "1"
+    } } }
+{ "text", { {
+      tags = {},
+      text = "0 = "
+    }, {
+      tags = {},
+      text = "0"
+    } } }
+{ "return" }
+]]--
\ No newline at end of file
diff --git a/test/tests/object constructor.lua b/test/tests/object constructor.lua
index 66030b1..669eb7c 100644
--- a/test/tests/object constructor.lua	
+++ b/test/tests/object constructor.lua	
@@ -14,7 +14,7 @@ _[12]={tags=_[21],text="hoho"}
 _[11]={tags=_[20],text="bar"}
 _[10]={tags=_[19],text=" == "}
 _[9]={tags=_[18],text="bar"}
-_[8]={tags=_[17],text="%object constructor.class::&object constructor.class"}
+_[8]={tags=_[17],text="%object constructor.class(c=hoho)::&object constructor.class"}
 _[7]={tags=_[16],text=", "}
 _[6]={tags=_[15],text="%object constructor.class::&object constructor.class"}
 _[5]={_[9],_[10],_[11],_[12],_[13],_[14]}
@@ -32,7 +32,7 @@ return {_[1],_[2],_[3]}
       text = ", "
     }, {
       tags = {},
-      text = "%object constructor.class::&object constructor.class"
+      text = "%object constructor.class(c=hoho)::&object constructor.class"
     } } }
 { "text", { {
       tags = {},