2.7 Parser tracing

parser/parser_tracing.go

@@ -0,0 +1,101 @@
+package parser
+
+import (
+	"fmt"
+	"strings"
+)
+
+// Parser tracing helps putting tracing statements in the methods of Parser to
+// see what was happening when parsing certain expressions.
+//
+// The file includes two function definitions that are really helpful when
+// trying to understand what the parser does: `trace` and `untrace`. Use them
+// like this:
+
+/*
+parser/parser.go
+
+func (p *Parser) parseExpressionStatement() *ast.ExpressionStatement {
+    defer untrace(trace("parseExpressionStatement"))
+	   // [...]
+}
+
+func (p *Parser) parseExpression(precedence int) ast.Expression {
+    defer untrace(trace("parseExpression"))
+	   // [...]
+}
+
+func (p *Parser) parseIntegerLiteral() ast.Expression {
+    defer untrace(trace("parseIntegerLiteral"))
+    // [...]
+}
+
+func (p *Parser) parsePrefixExpression() ast.Expression {
+    defer untrace(trace("parsePrefixExpression"))
+    // [...]
+}
+
+func (p *Parser) parseInfixExpression(left ast.Expression) ast.Expression {
+    defer untrace(trace("parseInfixExpression"))
+    // [...]
+}
+*/
+
+// With these tracing statements included we can now use our parser and see what
+// it does. Here is the output when parsing the expression statement
+// `-1 * 2 + 3` in the test suite:
+
+/*
+$ go test -v -run TestOperatorPrecedenceParsing ./parser
+=== RUN		TestOperatorPrecedenceParsing
+BEGIN parseExpressionStatement
+	BEGIN parseExpression
+		BEGIN parsePrefixExpression
+			BEGIN parseExpression
+				BEGIN parseIntegerLiteral
+				END parseIntegerLiteral
+			END parseExpression
+		END parsePrefixExpression
+		BEGIN parseInfixExpression
+			BEGIN parseExpression
+				BEGIN parseIntegerLiteral
+				END parseIntegerLiteral
+			END parseExpression
+		END parseInfixExpression
+		BEGIN parseInfixExpression
+			BEGIN parseExpression
+				BEGIN parseIntegerLiteral
+				END parseIntegerLiteral
+			END parseExpression
+		END parseInfixExpression
+	END parseExpression
+END parseExpressionStatement
+--- PASS: TestOperatorPrecedenceParsing (0.00s)
+PASS
+*/
+
+var traceLevel int = 0
+
+const traceIdentPlaceholder string = "\t"
+
+func identLevel() string {
+	return strings.Repeat(traceIdentPlaceholder, traceLevel-1)
+}
+
+func tracePrint(fs string) {
+	fmt.Printf("%s%s\n", identLevel(), fs)
+}
+
+func incIdent() { traceLevel = traceLevel + 1 }
+func decIdent() { traceLevel = traceLevel - 1 }
+
+func trace(msg string) string {
+	incIdent()
+	tracePrint("BEGIN " + msg)
+	return msg
+}
+
+func untrace(msg string) {
+	tracePrint("END " + msg)
+	decIdent()
+}