Make -d, -da, and -dt print to stdout and exit (#155)

Move debug arguments to separate section in -h/--help output.

Remove unused fields from parser struct.

Make -d, -da, and -dt args print to stdout and stderr, and make goawk
exit if any of them are specified.

goawk.go

@@ -52,11 +52,7 @@ const (
   -f progfile       load AWK source from progfile (multiple allowed)
   -v var=value      variable assignment (multiple allowed)
 
-Additional GoAWK arguments:
-  -cpuprofile file  write CPU profile to file
-  -d                print parsed syntax tree to stderr (debug mode)
-  -da               print virtual machine assembly instructions to stderr
-  -dt               print variable type information to stderr
+Additional GoAWK features:
   -E progfile       load program, treat as last option, disable var=value args
   -H                parse header row and enable @"field" in CSV input mode
   -h, --help        show this help message
@@ -65,6 +61,13 @@ Additional GoAWK arguments:
   -o mode           use CSV output for print with args (ignore OFS and ORS)
                     'csv|tsv [separator=<char>]'
   -version          show GoAWK version and exit
+
+GoAWK debugging arguments:
+  -cpuprofile file  write CPU profile to file
+  -d                print parsed syntax tree to stdout and exit
+  -da               print VM assembly instructions to stdout and exit
+  -dt               print variable type information to stdout and exit
+  -memprofile file  write memory profile to file
 `
 )
 
@@ -231,7 +234,7 @@ argsLoop:
 	// Parse source code and setup interpreter
 	parserConfig := &parser.ParserConfig{
 		DebugTypes:  debugTypes,
-		DebugWriter: os.Stderr,
+		DebugWriter: os.Stdout,
 	}
 	prog, err := parser.ParseProgram(fileReader.Source(), parserConfig)
 	if err != nil {
@@ -246,16 +249,20 @@ argsLoop:
 	}
 
 	if debug {
-		fmt.Fprintln(os.Stderr, prog)
+		fmt.Fprintln(os.Stdout, prog)
 	}
 
 	if debugAsm {
-		err := prog.Disassemble(os.Stderr)
+		err := prog.Disassemble(os.Stdout)
 		if err != nil {
 			errorExitf("could not disassemble program: %v", err)
 		}
 	}
 
+	if debug || debugAsm || debugTypes {
+		os.Exit(0)
+	}
+
 	if header {
 		if inputMode == "" {
 			errorExitf("-H only allowed together with -i")

parser/parser.go

@@ -76,10 +76,6 @@ func ParseProgram(src []byte, config *ParserConfig) (prog *Program, err error) {
 	}()
 	lexer := NewLexer(src)
 	p := parser{lexer: lexer}
-	if config != nil {
-		p.debugTypes = config.DebugTypes
-		p.debugWriter = config.DebugWriter
-	}
 	p.multiExprs = make(map[*ast.MultiExpr]Position, 3)
 
 	p.next() // initialize p.tok
@@ -136,10 +132,6 @@ type parser struct {
 
 	// Variable tracking and resolving
 	multiExprs map[*ast.MultiExpr]Position // tracks comma-separated expressions
-
-	// Configuration and debugging
-	debugTypes  bool      // show variable types for debugging
-	debugWriter io.Writer // where the debug output goes
 }
 
 // Parse an entire AWK program.