ast and parser

git-svn-id: https://svn.tlawal.org/svn/monkey@7 f6afcba9-9ef1-4bdd-9b72-7484f5705bac

ast/ast.go

@@ -0,0 +1,50 @@
+package ast
+
+import "monkey/token"
+
+type Node interface {
+	TokenLiteral() string
+}
+
+type Statement interface {
+	Node
+	statementNode()
+}
+
+type Expression interface {
+	Node
+	expressionNode()
+}
+
+type Identifier struct {
+	Token token.Token // the token.IDENT token
+	Value string
+}
+
+type Program struct {
+	Statements []Statement
+}
+
+type LetStatement struct {
+	Token token.Token // the token.LET token
+	Name  *Identifier
+	Value Expression
+}
+
+func (ls *LetStatement) stamementNode() {}
+func (ls *LetStatement) TokenLiteral() string {
+	return ls.Token.Literal
+}
+
+func (i *Identifier) expressionNode() {}
+func (i *Identifier) TokenLiteral() string {
+	return i.Token.Literal
+}
+
+func (p *Program) TokenLiteral() string {
+	if len(p.Statements) > 0 {
+		return p.Statements[0].TokenLiteral()
+	} else {
+		return ""
+	}
+}

parser/parser.go

@@ -0,0 +1,39 @@
+/* NOTE(tijani): 
+ * l_ in variables names stand for local_ identifiers. The reason is because I do not like
+ * single letter variable names, but I also do not want to confuse the myself 
+ * when I come back to reading this code after a while hence l_ to signify that it is local to that function.
+*/
+
+package parser
+
+import (
+	"monkey/ast"
+	"monkey/lexer"
+	"monkey/token"
+)
+
+type Parser struct {
+	l_lexer *lexer.Lexer
+	current_token token.Token
+	peek_token token.Token
+}
+
+func (l_parser *Parser) next_token(){
+	l_parser.current_token	 = l_parser.peek_token 
+	l_parser.peek_token = l_parser.l_lexer.NextToken() 
+}
+
+func (p *Parser) ParseProgram() *ast.Program {
+	return nil
+}
+
+func New(lexer *lexer.Lexer) *Parser {
+	l_parser := &Parser {l_lexer: lexer}
+	// Read two tokens so current_token and peek_token are set.
+	// NOTE(tijani): the first time l_parser.next_token() is called, current_token and peek_token will be pointing to the same token.
+	l_parser.next_token()
+	l_parser.next_token()
+
+	return l_parser
+}
+

parser/parser_test.go

@@ -0,0 +1,63 @@
+package parser
+
+import (
+	"monkey/ast"
+	"monkey/lexer"
+	"testing"
+)
+
+func TestLetStatement(t *testing.T) {
+	input := `
+				let x = 5;
+				let y = 10;
+				let foobar = 878688;
+	`
+	l_lexer := lexer.New(input)
+	l_parser = New(l_lexer)
+
+	program := l_parser.ParseProgram()
+	if program == nil {
+		t.Fatalf("ParseProgram() returned nil")
+	}
+	if len(program.Statements) != 3 {
+		t.Fatalf("program.Statements does not contain 3 statements, got=%d", len(program.Statements))
+	}
+
+	tests := []struct {
+		expetedIdentifier string
+	}{
+		{"x"},
+		{"y"},
+		{"foobar"},
+	}
+
+	for i, tt := range tests {
+		stmt := program.Statements[i]
+		if !testLetStatement(t, stmt, tt.expectedIdentifier) {
+			return
+		}
+	}
+}
+
+func testLetStatement(t *testing.T, s ast.Statement, name string) bool {
+	if s.TokenLiteral() != "let" {
+		t.Errorf("s.TokenLiteral not 'let', got=%q", s.TokenLiteral())
+		return false
+	}
+
+	letStmt, ok := s.(*ast.LetStatement)
+	if !ok {
+		t.Errorf("s not *ast.LetStatement, got=%T", s)
+		return false
+	}
+
+	if letStmt.Name.Value != name {
+		t.Errorf("letStmt.Name.Value not '%s', got=%s", name, letStmt.Name.Value)
+		return false
+	}
+
+	if letStmt.Name.TokenLiteral() != name {
+		e.Errorf("letStmt.Name.TokenLiteral() not '%s', got=%s", name, letStmt.Name.TokenLiteral())
+	}
+	return true
+}