feat: initial and partial support of composite expressions (#9)

A new `Composite` token is created. Literal composite expressions
are recognized and partially handled by the parser but not yet
by the code generator.

Other cosmetic changes are present.

lang/token.go

@@ -111,6 +111,7 @@ const (
 	// Internal virtual machine tokens (no corresponding keyword).
 	Call
 	CallX
+	Composite
 	EqualSet
 	Grow
 	Index

parser/compiler.go

@@ -134,6 +134,9 @@ func (c *Compiler) Codegen(tokens Tokens) (err error) {
 			}
 			emit(int64(t.Pos), vm.CallX, int64(t.Beg))
 
+		case lang.Composite:
+			log.Println("COMPOSITE")
+
 		case lang.Grow:
 			emit(int64(t.Pos), vm.Grow, int64(t.Beg))
 

parser/decl.go

@@ -280,10 +280,11 @@ func (p *Parser) parseTypeLine(in Tokens) (out Tokens, err error) {
 	if isAlias {
 		toks = toks[1:]
 	}
-	typ, err := p.ParseTypeExpr(toks)
+	typ, err := p.parseTypeExpr(toks)
 	if err != nil {
 		return out, err
 	}
+	typ.Name = in[0].Str
 	p.addSym(unsetAddr, in[0].Str, vm.NewValue(typ), symType, typ, p.funcScope != "")
 	return out, err
 }

parser/expr.go

@@ -7,10 +7,11 @@ import (
 
 	"github.com/mvertes/parscan/lang"
 	"github.com/mvertes/parscan/scanner"
+	"github.com/mvertes/parscan/vm"
 )
 
 func (p *Parser) parseExpr(in Tokens) (out Tokens, err error) {
-	log.Println("ParseExpr in:", in)
+	log.Println("parseExpr in:", in)
 	var ops, selectors Tokens
 	var vl int
 	var selectorIndex string
@@ -84,6 +85,24 @@ func (p *Parser) parseExpr(in Tokens) (out Tokens, err error) {
 			out = append(out, t)
 			vl++
 			ops = append(ops, scanner.Token{Tok: lang.Call, Pos: t.Pos, Beg: p.numItems(t.Block(), lang.Comma)})
+		case lang.BraceBlock:
+			// the block can be a func body or a composite type content.
+			// In both cases it is preceded by a type definition. We must determine the starting token of type def,
+			// parse the type def, and substitute the type def by a single ident.
+			// TODO: handle implicit type in composite expression.
+			ti := p.typeStartIndex(in[:len(in)-1])
+			if ti == -1 {
+				return out, ErrInvalidType
+			}
+			typ, err := p.parseTypeExpr(in[ti : len(in)-1])
+			if err != nil {
+				return out, ErrInvalidType
+			}
+			p.addSym(unsetAddr, typ.String(), vm.NewValue(typ), symType, typ, p.funcScope != "")
+			out = append(out, t, scanner.Token{Tok: lang.Ident, Pos: t.Pos, Str: typ.String()})
+			i = ti
+			vl += 2
+			ops = append(ops, scanner.Token{Tok: lang.Composite, Pos: t.Pos})
 		case lang.BracketBlock:
 			out = append(out, t)
 			vl++
@@ -113,7 +132,7 @@ func (p *Parser) parseExpr(in Tokens) (out Tokens, err error) {
 	}
 	out = append(out, ops...)
 
-	log.Println("ParseExpr out:", out, "vl:", vl, "ops:", ops)
+	log.Println("parseExpr out:", out, "vl:", vl, "ops:", ops)
 	// A logical operator (&&, ||) involves additional control flow operations.
 	if out, err = p.parseLogical(out); err != nil {
 		return out, err
@@ -133,7 +152,7 @@ func (p *Parser) parseExpr(in Tokens) (out Tokens, err error) {
 		t := out[i]
 		var toks Tokens
 		switch t.Tok {
-		case lang.ParenBlock, lang.BracketBlock:
+		case lang.ParenBlock, lang.BracketBlock, lang.BraceBlock:
 			if toks, err = p.parseExprStr(t.Block()); err != nil {
 				return out, err
 			}

parser/interpreter_test.go

@@ -255,3 +255,11 @@ func TestImport(t *testing.T) {
 		{src: `import . "fmt"; Println(4)`, res: "<nil>"},
 	})
 }
+
+func TestComposite(t *testing.T) {
+	run(t, []etest{
+		{src: "type T struct{}; t := T{}; t", res: "{}"},
+		{src: "t := struct{}{}; t", res: "{}"},
+		//		{src: "type T struct{N int}; t := T{2}; t", res: "{2}"},
+	})
+}

parser/parse.go

@@ -74,7 +74,7 @@ func (p *Parser) parseStmt(in Tokens) (out Tokens, err error) {
 	if len(in) == 0 {
 		return nil, nil
 	}
-	log.Println("ParseStmt in:", in)
+	log.Println("parseStmt in:", in)
 	switch t := in[0]; t.Tok {
 	case lang.Break:
 		return p.parseBreak(in)
@@ -249,7 +249,7 @@ func (p *Parser) parseFunc(in Tokens) (out Tokens, err error) {
 	if bi < 0 {
 		return out, fmt.Errorf("no function body")
 	}
-	typ, err := p.ParseTypeExpr(in[:bi])
+	typ, err := p.parseTypeExpr(in[:bi])
 	if err != nil {
 		return out, err
 	}

parser/type.go

@@ -26,12 +26,10 @@ var (
 	ErrTypeNotImplemented = errors.New("not implemented")
 )
 
-// ParseTypeExpr parses a list of tokens defining a type expresssion and returns
-// the corresponding runtime type or an error.
-func (p *Parser) ParseTypeExpr(in Tokens) (typ *vm.Type, err error) {
+func (p *Parser) parseTypeExpr(in Tokens) (typ *vm.Type, err error) {
 	switch in[0].Tok {
 	case lang.BracketBlock:
-		typ, err := p.ParseTypeExpr(in[1:])
+		typ, err := p.parseTypeExpr(in[1:])
 		if err != nil {
 			return nil, err
 		}
@@ -53,7 +51,7 @@ func (p *Parser) ParseTypeExpr(in Tokens) (typ *vm.Type, err error) {
 		return vm.SliceOf(typ), nil
 
 	case lang.Mul:
-		typ, err := p.ParseTypeExpr(in[1:])
+		typ, err := p.parseTypeExpr(in[1:])
 		if err != nil {
 			return nil, err
 		}
@@ -157,7 +155,7 @@ func (p *Parser) parseParamTypes(in Tokens, flag typeFlag) (types []*vm.Type, va
 				continue
 			}
 		}
-		typ, err := p.ParseTypeExpr(t)
+		typ, err := p.parseTypeExpr(t)
 		if err != nil {
 			return nil, nil, err
 		}
@@ -196,3 +194,17 @@ func (p *Parser) hasFirstParam(in Tokens) bool {
 	s, _, ok := p.getSym(in[0].Str, p.scope)
 	return !ok || s.kind != symType
 }
+
+// typeStartIndex returns the index of the start of type expression in tokens, or -1.
+func (p *Parser) typeStartIndex(in Tokens) int {
+	index := len(in) - 1
+	for i := index; i >= 0; i-- {
+		switch in[i].Tok {
+		case lang.Ident, lang.Struct, lang.Map, lang.Func, lang.Interface, lang.Mul, lang.BraceBlock, lang.BracketBlock, lang.ParenBlock:
+			index = i
+		default:
+			return index
+		}
+	}
+	return -1
+}

vm/type.go

@@ -10,10 +10,19 @@ type Type struct {
 	Rtype reflect.Type
 }
 
+func (t *Type) String() string {
+	if t.Name != "" {
+		return t.Name
+	}
+	return t.Rtype.String()
+}
+
+// Elem returns a type's element type.
 func (t *Type) Elem() *Type {
 	return &Type{Rtype: t.Rtype.Elem()}
 }
 
+// Out returns the type's i'th output parameter.
 func (t *Type) Out(i int) *Type {
 	return &Type{Rtype: t.Rtype.Out(i)}
 }
@@ -43,18 +52,22 @@ func ValueOf(v any) Value {
 	return Value{Data: reflect.ValueOf(v)}
 }
 
+// PointerTo returns the pointer type with element t.
 func PointerTo(t *Type) *Type {
 	return &Type{Rtype: reflect.PointerTo(t.Rtype)}
 }
 
-func ArrayOf(size int, t *Type) *Type {
-	return &Type{Rtype: reflect.ArrayOf(size, t.Rtype)}
+// ArrayOf returns the array type with the given length and element type.
+func ArrayOf(length int, t *Type) *Type {
+	return &Type{Rtype: reflect.ArrayOf(length, t.Rtype)}
 }
 
+// SliceOf returns the slice type with the given element type.
 func SliceOf(t *Type) *Type {
 	return &Type{Rtype: reflect.SliceOf(t.Rtype)}
 }
 
+// FuncOf returns the function type with the given argument and result types.
 func FuncOf(arg, ret []*Type, variadic bool) *Type {
 	a := make([]reflect.Type, len(arg))
 	for i, e := range arg {
@@ -67,6 +80,7 @@ func FuncOf(arg, ret []*Type, variadic bool) *Type {
 	return &Type{Rtype: reflect.FuncOf(a, r, variadic)}
 }
 
+// StructOf returns the struct type with the given field types.
 func StructOf(fields []*Type) *Type {
 	rf := make([]reflect.StructField, len(fields))
 	for i, f := range fields {

vm/vm.go

@@ -1,3 +1,4 @@
+// Package vm implement a stack based virtual machine.
 package vm
 
 import (
@@ -85,6 +86,7 @@ var strop = [...]string{ // for VM tracing.
 	Vassign:      "Vassign",
 }
 
+// Code represents the virtual machine byte code.
 type Code [][]int64
 
 // Machine represents a virtual machine.
@@ -256,39 +258,47 @@ func (m *Machine) Run() (err error) {
 	}
 }
 
+// PushCode adds instructions to the machine code.
 func (m *Machine) PushCode(code ...[]int64) (p int) {
 	p = len(m.code)
 	m.code = append(m.code, code...)
 	return p
 }
 
+// SetIP sets the value of machine instruction pointer to given index.
 func (m *Machine) SetIP(ip int) { m.ip = ip }
+
+// Push pushes data values on top of machine memory stack.
 func (m *Machine) Push(v ...Value) (l int) {
 	l = len(m.mem)
 	m.mem = append(m.mem, v...)
 	return l
 }
 
+// Pop removes and returns the value on the top of machine stack.
 func (m *Machine) Pop() (v Value) {
 	l := len(m.mem) - 1
 	v = m.mem[l]
 	m.mem = m.mem[:l]
 	return v
 }
 
+// Top returns (but not remove)  the value on the top of machine stack.
 func (m *Machine) Top() (v Value) {
 	if l := len(m.mem); l > 0 {
 		v = m.mem[l-1]
 	}
 	return v
 }
 
+// PopExit removes the last machine code instruction if is Exit.
 func (m *Machine) PopExit() {
 	if l := len(m.code); l > 0 && m.code[l-1][1] == Exit {
 		m.code = m.code[:l-1]
 	}
 }
 
+// CodeString returns the string representation of a machine code instruction.
 func CodeString(op []int64) string {
 	switch len(op) {
 	case 2:
@@ -317,6 +327,7 @@ func slint(a []int64) []int {
 	return r
 }
 
+// Vstring returns the string repreentation of a list of values.
 func Vstring(lv []Value) string {
 	s := "["
 	for _, v := range lv {