From 9b055554f3041bf94f47bef9747f9f291b0f7392 Mon Sep 17 00:00:00 2001
From: alandonovan <adonovan@google.com>
Date: Fri, 2 Nov 2018 14:29:51 -0400
Subject: [PATCH] compile: add missing opcodeName[EXCH] (#5)

Also,
- make Opcode.String catch future missing entries.
- document (*Function).Param.
---
 internal/compile/compile.go | 5 ++++-
 starlark/value.go           | 3 +++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/internal/compile/compile.go b/internal/compile/compile.go
index 99e9d542..8da415b8 100644
--- a/internal/compile/compile.go
+++ b/internal/compile/compile.go
@@ -152,6 +152,7 @@ var opcodeNames = [...]string{
 	DUP2:        "dup2",
 	DUP:         "dup",
 	EQL:         "eql",
+	EXCH:        "exch",
 	FALSE:       "false",
 	FREE:        "free",
 	GE:          "ge",
@@ -271,7 +272,9 @@ var stackEffect = [...]int8{
 
 func (op Opcode) String() string {
 	if op < OpcodeMax {
-		return opcodeNames[op]
+		if name := opcodeNames[op]; name != "" {
+			return name
+		}
 	}
 	return fmt.Sprintf("illegal op (%d)", op)
 }
diff --git a/starlark/value.go b/starlark/value.go
index 880329a5..9ec67c82 100644
--- a/starlark/value.go
+++ b/starlark/value.go
@@ -547,6 +547,9 @@ func (fn *Function) Globals() StringDict {
 
 func (fn *Function) Position() syntax.Position { return fn.funcode.Pos }
 func (fn *Function) NumParams() int            { return fn.funcode.NumParams }
+
+// Param returns the name and position of the ith parameter,
+// where 0 <= i < NumParams().
 func (fn *Function) Param(i int) (string, syntax.Position) {
 	id := fn.funcode.Locals[i]
 	return id.Name, id.Pos