Adds a dummy method to atom so the compiler checks that only valid atoms are allowed

2 files changed, 27 insertions, 11 deletions

diff --git a/subex/parse.go b/subex/parse.go
index 8b3a553..d6ef995 100644
--- a/subex/parse.go
+++ b/subex/parse.go
@@ -109,7 +109,7 @@ func parseReplacement(l *RuneReader) (output []OutputContent) {
 			case '@', '~', '#':
 				output = append(output, OutputAtomLiteral{atom: parseTerminatorAtomLiteral(r, l)})
 			default:
-				output = append(output, OutputAtomLiteral{atom: r})
+				output = append(output, OutputAtomLiteral{atom: walk.StringAtom(r)})
 		}
 	}
 	return output
@@ -143,10 +143,10 @@ func parseRangeSubex(l *RuneReader) map[walk.Atom]walk.Atom {
 				fromsEnd = fromsStart
 			}
 			for i := fromsStart; i <= fromsEnd; i += 1 {
-				froms = append(froms, i)
+				froms = append(froms, walk.StringAtom(i))
 			}
 		} else {
-			froms = append(froms, fromsStart)
+			froms = append(froms, walk.StringAtom(fromsStart))
 		}
 	}
 	if len(froms) == 0 {
@@ -173,10 +173,10 @@ func parseRangeSubex(l *RuneReader) map[walk.Atom]walk.Atom {
 					tosEnd = tosStart
 				}
 				for i := tosStart; i <= tosEnd; i += 1 {
-					tos = append(tos, i)
+					tos = append(tos, walk.StringAtom(i))
 				}
 			} else {
-				tos = append(tos, tosStart)
+				tos = append(tos, walk.StringAtom(tosStart))
 			}
 		}
 	} else {
@@ -217,7 +217,7 @@ func parseSubex(l *RuneReader, minPower int) SubexAST {
 		case '@', '#', '~':
 			lhs = SubexASTCopyAtom{atom: parseTerminatorAtomLiteral(r, l)}
 		default:
-			lhs = SubexASTCopyAtom{atom: r}
+			lhs = SubexASTCopyAtom{atom: walk.StringAtom(r)}
 	}
 	loop: for {
 		if minPower <= 0 {
diff --git a/walk/walk.go b/walk/walk.go
index 36e9805..64f16ac 100644
--- a/walk/walk.go
+++ b/walk/walk.go
@@ -34,6 +34,7 @@ func (value TerminalValue) String() string {
 			panic("Unknown TerminalValue")
 	}
 }
+func (value TerminalValue) atomness() {}
 
 type ValueNull struct {}
 func (value ValueNull) Pieces(out chan<- Atom) {
@@ -42,6 +43,8 @@ func (value ValueNull) Pieces(out chan<- Atom) {
 func (value ValueNull) String() string {
 	return "null"
 }
+func (value ValueNull) atomness() {}
+
 type ValueBool bool
 func (value ValueBool) Pieces(out chan<- Atom) {
 	out<-value
@@ -53,6 +56,8 @@ func (value ValueBool) String() string {
 		return "false"
 	}
 }
+func (value ValueBool) atomness() {}
+
 type ValueNumber float64
 func (value ValueNumber) Pieces(out chan<- Atom) {
 	out<-value
@@ -61,14 +66,22 @@ func (value ValueNumber) String() string {
 	v := float64(value)
 	return fmt.Sprintf("%f", v)
 }
+func (value ValueNumber) atomness() {}
 
 type StartString struct {}
+func (value StartString) atomness() {}
+
 type EndString struct {}
+func (value EndString) atomness() {}
+
+type StringAtom rune
+func (value StringAtom) atomness() {}
+
 type ValueString string
 func (value ValueString) Pieces(out chan<- Atom) {
 	out<-StartString{}
 	for _, char := range value {
-		out<-char
+		out<-StringAtom(char)
 	}
 	out<-EndString{}
 }
@@ -76,7 +89,10 @@ func (value ValueString) String() string {
 	return fmt.Sprintf("\"%s\"", string(value))
 }
 
-type Atom interface {}
+type Atom interface {
+	// Something so the compiler will check that only certain types are being cast into Atoms
+	atomness()
+}
 
 type WalkValue interface {
 	Pieces(out chan<- Atom)
@@ -458,7 +474,7 @@ func Compound(in <-chan Atom) <-chan CompoundResult {
 				case ValueNumber:
 					out<-CompoundResult{v, nil}
 					continue
-				case rune:
+				case StringAtom:
 					out<-CompoundResult{nil, CompoundRuneOutsideString}
 					break outer
 				case EndString:
@@ -480,8 +496,8 @@ func Compound(in <-chan Atom) <-chan CompoundResult {
 				switch v := atom.(type) {
 					case EndString:
 						break loop
-					case rune:
-						builder.WriteRune(v)
+					case StringAtom:
+						builder.WriteRune(rune(v))
 					default:
 						out<-CompoundResult{nil, CompoundInvalidStringAtom}
 						break outer