Add --only-parse option to the parse command

When this option is enabled, the parser performs only parse and doesn't semantic actions.

2 files changed, 32 insertions, 17 deletions

diff --git a/cmd/vartan/parse.go b/cmd/vartan/parse.go
index 1311ce6..d5e3d36 100644
--- a/cmd/vartan/parse.go
+++ b/cmd/vartan/parse.go
@@ -12,8 +12,9 @@ import (
 )
 
 var parseFlags = struct {
-	source *string
-	cst    *bool
+	source    *string
+	onlyParse *bool
+	cst       *bool
 }{}
 
 func init() {
@@ -25,6 +26,7 @@ func init() {
 		RunE:    runParse,
 	}
 	parseFlags.source = cmd.Flags().StringP("source", "s", "", "source file path (default stdin)")
+	parseFlags.onlyParse = cmd.Flags().Bool("only-parse", false, "when this option is enabled, the parser performs only parse and doesn't semantic actions")
 	parseFlags.cst = cmd.Flags().Bool("cst", false, "when this option is enabled, the parser generates a CST")
 	rootCmd.AddCommand(cmd)
 }
@@ -48,6 +50,10 @@ func runParse(cmd *cobra.Command, args []string) (retErr error) {
 		}
 	}()
 
+	if *parseFlags.onlyParse && *parseFlags.cst {
+		return fmt.Errorf("You cannot enable --only-parse and --cst at the same time")
+	}
+
 	cgram, err := readCompiledGrammar(args[0])
 	if err != nil {
 		return fmt.Errorf("Cannot read a compiled grammar: %w", err)
@@ -66,9 +72,10 @@ func runParse(cmd *cobra.Command, args []string) (retErr error) {
 		}
 
 		var opts []driver.ParserOption
-		if *parseFlags.cst {
+		switch {
+		case *parseFlags.cst:
 			opts = append(opts, driver.MakeCST())
-		} else {
+		case !*parseFlags.onlyParse:
 			opts = append(opts, driver.MakeAST())
 		}
 		p, err = driver.NewParser(cgram, src, opts...)
@@ -82,14 +89,17 @@ func runParse(cmd *cobra.Command, args []string) (retErr error) {
 		return err
 	}
 
-	var tree *driver.Node
-	if *parseFlags.cst {
-		tree = p.CST()
-	} else {
-		tree = p.AST()
-	}
 	fmt.Printf("Accepted\n")
-	driver.PrintTree(os.Stdout, tree)
+
+	if !*parseFlags.onlyParse {
+		var tree *driver.Node
+		if *parseFlags.cst {
+			tree = p.CST()
+		} else {
+			tree = p.AST()
+		}
+		driver.PrintTree(os.Stdout, tree)
+	}
 
 	return nil
 }
diff --git a/driver/parser.go b/driver/parser.go
index cdcaf14..a96f89a 100644
--- a/driver/parser.go
+++ b/driver/parser.go
@@ -81,6 +81,7 @@ type Parser struct {
 	ast        *Node
 	makeAST    bool
 	makeCST    bool
+	needSemAct bool
 }
 
 func NewParser(gram *spec.CompiledGrammar, src io.Reader, opts ...ParserOption) (*Parser, error) {
@@ -93,7 +94,6 @@ func NewParser(gram *spec.CompiledGrammar, src io.Reader, opts ...ParserOption)
 		gram:       gram,
 		lex:        lex,
 		stateStack: []int{},
-		semStack:   []*semanticFrame{},
 	}
 
 	for _, opt := range opts {
@@ -103,6 +103,8 @@ func NewParser(gram *spec.CompiledGrammar, src io.Reader, opts ...ParserOption)
 		}
 	}
 
+	p.needSemAct = p.makeAST || p.makeCST
+
 	return p, nil
 }
 
@@ -130,7 +132,7 @@ func (p *Parser) Parse() error {
 			}
 
 			// semantic action
-			{
+			if p.needSemAct {
 				var ast *Node
 				var cst *Node
 				if p.makeAST {
@@ -154,14 +156,17 @@ func (p *Parser) Parse() error {
 		case act > 0: // Reduce
 			accepted := p.reduce(act)
 			if accepted {
-				top := p.semStack[len(p.semStack)-1]
-				p.cst = top.cst
-				p.ast = top.ast
+				if p.needSemAct {
+					top := p.semStack[len(p.semStack)-1]
+					p.cst = top.cst
+					p.ast = top.ast
+				}
+
 				return nil
 			}
 
 			// semantic action
-			{
+			if p.needSemAct {
 				prodNum := act
 				lhs := p.gram.ParsingTable.LHSSymbols[prodNum]