From 42f0367a94d709beb23b93e3cd7104f78adb6da4 Mon Sep 17 00:00:00 2001
From: Eduard Urbach <admin@akyoto.dev>
Date: Mon, 5 Aug 2024 12:39:07 +0200
Subject: [PATCH] Implemented multiple return values

---
 README.md                                |  2 +-
 lib/log/number.q                         |  9 +++--
 src/build/arch/x64/Return.go             |  2 +-
 src/build/ast/Count.go                   |  4 +-
 src/build/ast/Return.go                  |  2 +-
 src/build/ast/parseKeyword.go            |  4 +-
 src/build/core/CompileASTNode.go         |  5 ++-
 src/build/core/CompileCall.go            |  1 +
 src/build/core/CompileDefinition.go      | 48 +++++++++++++++---------
 src/build/core/CompileReturn.go          |  4 +-
 src/build/core/Define.go                 | 31 +++++++++++++++
 src/build/core/ExpressionToRegister.go   |  5 +--
 src/build/core/ExpressionsToRegisters.go |  2 +-
 tests/programs/return-multi.q            | 28 ++++++++++++++
 tests/programs_test.go                   |  1 +
 15 files changed, 113 insertions(+), 35 deletions(-)
 create mode 100644 src/build/core/Define.go
 create mode 100644 tests/programs/return-multi.q

diff --git a/README.md b/README.md
index 8ba0c76..d48bd05 100644
--- a/README.md
+++ b/README.md
@@ -115,11 +115,11 @@ This is what generates expressions from tokens.
 - [x] Loops
 - [x] Hexadecimal, octal and binary literals
 - [x] Escape sequences
+- [x] Multiple return values
 - [ ] Data structures
 - [ ] Type system
 - [ ] Type operator: `|` (`User | Error`)
 - [ ] Error handling
-- [ ] Multiple return values
 - [ ] Threading library
 - [ ] Self-hosted compiler
 
diff --git a/lib/log/number.q b/lib/log/number.q
index 01471dc..86be427 100644
--- a/lib/log/number.q
+++ b/lib/log/number.q
@@ -4,13 +4,14 @@ import sys
 number(x) {
 	length := 20
 	buffer := mem.alloc(length)
-	tmp := itoa(x, buffer, length)
-	sys.write(1, tmp, buffer + length - tmp)
+	address, count := itoa(x, buffer, length)
+	sys.write(1, address, count)
 	mem.free(buffer, length)
 }
 
 itoa(x, buffer, length) {
-	tmp := buffer + length
+	end := buffer + length
+	tmp := end
 	digit := 0
 
 	loop {
@@ -19,7 +20,7 @@ itoa(x, buffer, length) {
 		tmp[0] = '0' + digit
 
 		if x == 0 {
-			return tmp
+			return tmp, end - tmp
 		}
 	}
 }
\ No newline at end of file
diff --git a/src/build/arch/x64/Return.go b/src/build/arch/x64/Return.go
index dc185da..a64d39f 100644
--- a/src/build/arch/x64/Return.go
+++ b/src/build/arch/x64/Return.go
@@ -3,5 +3,5 @@ package x64
 // Return transfers program control to a return address located on the top of the stack.
 // The address is usually placed on the stack by a Call instruction.
 func Return(code []byte) []byte {
-	return append(code, 0xc3)
+	return append(code, 0xC3)
 }
diff --git a/src/build/ast/Count.go b/src/build/ast/Count.go
index 192a36f..2c61203 100644
--- a/src/build/ast/Count.go
+++ b/src/build/ast/Count.go
@@ -29,8 +29,8 @@ func Count(body AST, buffer []byte, kind token.Kind, name string) uint8 {
 			count += Count(node.Body, buffer, kind, name)
 
 		case *Return:
-			if node.Value != nil {
-				count += node.Value.Count(buffer, kind, name)
+			for _, value := range node.Values {
+				count += value.Count(buffer, kind, name)
 			}
 
 		case *Switch:
diff --git a/src/build/ast/Return.go b/src/build/ast/Return.go
index 37574e2..6c8aa2d 100644
--- a/src/build/ast/Return.go
+++ b/src/build/ast/Return.go
@@ -6,5 +6,5 @@ import (
 
 // Return represents a return statement.
 type Return struct {
-	Value *expression.Expression
+	Values []*expression.Expression
 }
diff --git a/src/build/ast/parseKeyword.go b/src/build/ast/parseKeyword.go
index 0b6a423..f4a948a 100644
--- a/src/build/ast/parseKeyword.go
+++ b/src/build/ast/parseKeyword.go
@@ -48,8 +48,8 @@ func parseKeyword(tokens token.List, source []byte, nodes AST) (Node, error) {
 			return &Return{}, nil
 		}
 
-		value := expression.Parse(tokens[1:])
-		return &Return{Value: value}, nil
+		values := expression.NewList(tokens[1:])
+		return &Return{Values: values}, nil
 
 	case token.Switch:
 		blockStart := tokens.IndexKind(token.BlockStart)
diff --git a/src/build/core/CompileASTNode.go b/src/build/core/CompileASTNode.go
index e3bccaf..7277ccc 100644
--- a/src/build/core/CompileASTNode.go
+++ b/src/build/core/CompileASTNode.go
@@ -31,7 +31,10 @@ func (f *Function) CompileASTNode(node ast.Node) error {
 		return f.CompileLoop(node)
 
 	case *ast.Return:
-		f.Fold(node.Value)
+		for _, value := range node.Values {
+			f.Fold(value)
+		}
+
 		return f.CompileReturn(node)
 
 	case *ast.Switch:
diff --git a/src/build/core/CompileCall.go b/src/build/core/CompileCall.go
index 68e915a..c04f842 100644
--- a/src/build/core/CompileCall.go
+++ b/src/build/core/CompileCall.go
@@ -69,6 +69,7 @@ func (f *Function) CompileCall(root *expression.Expression) error {
 		return err
 	}
 
+	// TODO: Save all return value registers of the function
 	f.SaveRegister(f.CPU.Output[0])
 
 	// Push
diff --git a/src/build/core/CompileDefinition.go b/src/build/core/CompileDefinition.go
index 75241ba..689f020 100644
--- a/src/build/core/CompileDefinition.go
+++ b/src/build/core/CompileDefinition.go
@@ -1,36 +1,50 @@
 package core
 
 import (
+	"git.akyoto.dev/cli/q/src/build/asm"
 	"git.akyoto.dev/cli/q/src/build/ast"
 	"git.akyoto.dev/cli/q/src/build/errors"
-	"git.akyoto.dev/cli/q/src/build/scope"
-	"git.akyoto.dev/cli/q/src/build/token"
+	"git.akyoto.dev/cli/q/src/build/expression"
 )
 
 // CompileDefinition compiles a variable definition.
 func (f *Function) CompileDefinition(node *ast.Define) error {
 	left := node.Expression.Children[0]
 	right := node.Expression.Children[1]
-	name := left.Token.Text(f.File.Bytes)
 
-	if f.IdentifierExists(name) {
-		return errors.New(&errors.VariableAlreadyExists{Name: name}, f.File, left.Token.Position)
+	if left.IsLeaf() {
+		variable, err := f.Define(left)
+
+		if err != nil {
+			return err
+		}
+
+		err = f.ExpressionToRegister(right, variable.Register)
+		f.AddVariable(variable)
+		return err
 	}
 
-	uses := token.Count(f.Body, f.File.Bytes, token.Identifier, name) - 1
-
-	if uses == 0 {
-		return errors.New(&errors.UnusedVariable{Name: name}, f.File, left.Token.Position)
+	if !ast.IsFunctionCall(right) {
+		return errors.New(errors.NotImplemented, f.File, node.Expression.Token.Position)
 	}
 
-	register := f.NewRegister()
-	err := f.ExpressionToRegister(right, register)
+	count := 0
+	err := f.CompileCall(right)
 
-	f.AddVariable(&scope.Variable{
-		Name:     name,
-		Register: register,
-		Alive:    uses,
+	if err != nil {
+		return err
+	}
+
+	return left.EachLeaf(func(leaf *expression.Expression) error {
+		variable, err := f.Define(leaf)
+
+		if err != nil {
+			return err
+		}
+
+		f.RegisterRegister(asm.MOVE, variable.Register, f.CPU.Output[count])
+		f.AddVariable(variable)
+		count++
+		return nil
 	})
-
-	return err
 }
diff --git a/src/build/core/CompileReturn.go b/src/build/core/CompileReturn.go
index 26f1cab..ca59d56 100644
--- a/src/build/core/CompileReturn.go
+++ b/src/build/core/CompileReturn.go
@@ -8,9 +8,9 @@ import (
 func (f *Function) CompileReturn(node *ast.Return) error {
 	defer f.Return()
 
-	if node.Value == nil {
+	if len(node.Values) == 0 {
 		return nil
 	}
 
-	return f.ExpressionToRegister(node.Value, f.CPU.Output[0])
+	return f.ExpressionsToRegisters(node.Values, f.CPU.Output)
 }
diff --git a/src/build/core/Define.go b/src/build/core/Define.go
new file mode 100644
index 0000000..0867f1b
--- /dev/null
+++ b/src/build/core/Define.go
@@ -0,0 +1,31 @@
+package core
+
+import (
+	"git.akyoto.dev/cli/q/src/build/errors"
+	"git.akyoto.dev/cli/q/src/build/expression"
+	"git.akyoto.dev/cli/q/src/build/scope"
+	"git.akyoto.dev/cli/q/src/build/token"
+)
+
+// Define defines a new variable.
+func (f *Function) Define(leaf *expression.Expression) (*scope.Variable, error) {
+	name := leaf.Token.Text(f.File.Bytes)
+
+	if f.IdentifierExists(name) {
+		return nil, errors.New(&errors.VariableAlreadyExists{Name: name}, f.File, leaf.Token.Position)
+	}
+
+	uses := token.Count(f.Body, f.File.Bytes, token.Identifier, name) - 1
+
+	if uses == 0 {
+		return nil, errors.New(&errors.UnusedVariable{Name: name}, f.File, leaf.Token.Position)
+	}
+
+	variable := &scope.Variable{
+		Name:     name,
+		Register: f.NewRegister(),
+		Alive:    uses,
+	}
+
+	return variable, nil
+}
diff --git a/src/build/core/ExpressionToRegister.go b/src/build/core/ExpressionToRegister.go
index e115758..29a084c 100644
--- a/src/build/core/ExpressionToRegister.go
+++ b/src/build/core/ExpressionToRegister.go
@@ -11,8 +11,9 @@ import (
 
 // ExpressionToRegister puts the result of an expression into the specified register.
 func (f *Function) ExpressionToRegister(node *expression.Expression, register cpu.Register) error {
+	f.SaveRegister(register)
+
 	if node.IsFolded {
-		f.SaveRegister(register)
 		f.RegisterNumber(asm.MOVE, register, node.Value)
 		return nil
 	}
@@ -25,7 +26,6 @@ func (f *Function) ExpressionToRegister(node *expression.Expression, register cp
 		err := f.CompileCall(node)
 
 		if register != f.CPU.Output[0] {
-			f.SaveRegister(register)
 			f.RegisterRegister(asm.MOVE, register, f.CPU.Output[0])
 		}
 
@@ -70,7 +70,6 @@ func (f *Function) ExpressionToRegister(node *expression.Expression, register cp
 	err = f.Execute(node.Token, register, right)
 
 	if register != final {
-		f.SaveRegister(final)
 		f.RegisterRegister(asm.MOVE, final, register)
 		f.FreeRegister(register)
 	}
diff --git a/src/build/core/ExpressionsToRegisters.go b/src/build/core/ExpressionsToRegisters.go
index 64d6816..f3a09fe 100644
--- a/src/build/core/ExpressionsToRegisters.go
+++ b/src/build/core/ExpressionsToRegisters.go
@@ -7,7 +7,7 @@ import (
 
 // ExpressionsToRegisters moves multiple expressions into the specified registers.
 func (f *Function) ExpressionsToRegisters(expressions []*expression.Expression, registers []cpu.Register) error {
-	for i := len(registers) - 1; i >= 0; i-- {
+	for i := len(expressions) - 1; i >= 0; i-- {
 		err := f.ExpressionToRegister(expressions[i], registers[i])
 
 		if err != nil {
diff --git a/tests/programs/return-multi.q b/tests/programs/return-multi.q
new file mode 100644
index 0000000..47e72be
--- /dev/null
+++ b/tests/programs/return-multi.q
@@ -0,0 +1,28 @@
+main() {
+	a, b := reverse2(1, 2)
+	assert a == 2
+	assert b == 1
+
+	c, d, e := reverse3(1, 2, 3)
+	assert c == 3
+	assert d == 2
+	assert e == 1
+
+	f, g, h, i := mix4(1, 2, 3, 4)
+	assert f == 4 + 1
+	assert g == 3 + 2
+	assert h == 2 + 3
+	assert i == 1 + 4
+}
+
+reverse2(a, b) {
+	return b, a
+}
+
+reverse3(a, b, c) {
+	return c, b, a
+}
+
+mix4(a, b, c, d) {
+	return d + a, c + b, b + c, a + d
+}
\ No newline at end of file
diff --git a/tests/programs_test.go b/tests/programs_test.go
index c381573..39c5677 100644
--- a/tests/programs_test.go
+++ b/tests/programs_test.go
@@ -24,6 +24,7 @@ var programs = []struct {
 	{"reassign", "", "", 0},
 	{"reuse", "", "", 0},
 	{"return", "", "", 0},
+	{"return-multi", "", "", 0},
 	{"math", "", "", 0},
 	{"precedence", "", "", 0},
 	{"op-assign", "", "", 0},