Implement all unary and binary arithmetic operators.

R=rsc
APPROVED=rsc
DELTA=689  (497 added, 169 deleted, 23 changed)
OCL=31755
CL=31772

usr/austin/eval/decls.go

@@ -20,6 +20,8 @@ type Type interface {
 	// compatible returns true if this type is compatible with o.
 	// XXX Assignment versus comparison compatibility?
 	compatible(o Type) bool;
+	// isBoolean returns true if this is a boolean type.
+	isBoolean() bool;
 	// isInteger returns true if this is an integer type.
 	isInteger() bool;
 	// isFloat returns true if this is a floating type.

usr/austin/eval/type.go

@@ -29,6 +29,10 @@ import (
 type commonType struct {
 }
 
+func (commonType) isBoolean() bool {
+	return false;
+}
+
 func (commonType) isInteger() bool {
 	return false;
 }
@@ -55,6 +59,10 @@ func (t *boolType) compatible(o Type) bool {
 	return Type(t) == o;
 }
 
+func (t *boolType) isBoolean() bool {
+	return true;
+}
+
 func (boolType) String() string {
 	return "bool";
 }