Further simplifications to grammar

gg/decoder.go

@@ -12,13 +12,9 @@ import (
 	"golang.org/x/exp/slices"
 )
 
-func s(str string) fmt.Stringer {
-	return Stringer{S: str}
-}
-
 var (
 	notNewline = RuneFunc(
-		s("not-newline"), func(r rune) bool { return r != '\n' },
+		"not-newline", func(r rune) bool { return r != '\n' },
 	)
 
 	comment = Prefixed(
@@ -26,7 +22,7 @@ var (
 	)
 
 	whitespace = ZeroOrMore(FirstOf(
-		Discard(RuneFunc(s("whitespace"), unicode.IsSpace)),
+		Discard(RuneFunc("whitespace", unicode.IsSpace)),
 		Discard(comment),
 	))
 )
@@ -43,13 +39,12 @@ func trimmedRune(r rune) Symbol[Located[rune]] {
 
 var (
 	digit = RuneFunc(
-		s("digit"), func(r rune) bool { return '0' <= r && r <= '9' },
+		"digit", func(r rune) bool { return '0' <= r && r <= '9' },
 	)
 
 	positiveNumber = StringFromRunes(OneOrMore(digit))
 
 	negativeNumber = Reduction(
-		s("negative-number"),
 		Rune('-'),
 		positiveNumber,
 		func(neg Located[rune], posNum Located[string]) Located[string] {
@@ -57,23 +52,25 @@ var (
 		},
 	)
 
-	number = Mapping(
-		s("number"),
-		FirstOf(negativeNumber, positiveNumber),
-		func(str Located[string]) Located[Value] {
-			i, err := strconv.ParseInt(str.Value, 10, 64)
-			if err != nil {
-				panic(fmt.Errorf("parsing %q as int: %w", str, err))
-			}
+	number = Named(
+		"number",
+		Mapping(
+			FirstOf(negativeNumber, positiveNumber),
+			func(str Located[string]) Located[Value] {
+				i, err := strconv.ParseInt(str.Value, 10, 64)
+				if err != nil {
+					panic(fmt.Errorf("parsing %q as int: %w", str, err))
+				}
 
-			return Locate(str.Location, Number(i))
-		},
+				return Locate(str.Location, Number(i))
+			},
+		),
 	)
 )
 
 var (
 	letter = RuneFunc(
-		s("letter"),
+		"letter",
 		func(r rune) bool {
 			return unicode.In(r, unicode.Letter, unicode.Mark)
 		},
@@ -81,18 +78,20 @@ var (
 
 	nameTail = ZeroOrMore(FirstOf(letter, digit))
 
-	name = Reduction(
-		s("name"),
-		letter,
-		nameTail,
-		func(head Located[rune], tail []Located[rune]) Located[Value] {
-			name := make([]rune, 0, len(tail)+1)
-			name = append(name, head.Value)
-			for _, r := range tail {
-				name = append(name, r.Value)
-			}
-			return Locate(head.Location, Name(string(name)))
-		},
+	name = Named(
+		"name",
+		Reduction(
+			letter,
+			nameTail,
+			func(head Located[rune], tail []Located[rune]) Located[Value] {
+				name := make([]rune, 0, len(tail)+1)
+				name = append(name, head.Value)
+				for _, r := range tail {
+					name = append(name, r.Value)
+				}
+				return Locate(head.Location, Name(string(name)))
+			},
+		),
 	)
 )
 
@@ -122,10 +121,8 @@ var graphSym, value = func() (
 	}
 
 	var (
-		rightParen = trimmedRune(')')
-		tupleEnd   = Mapping(
-			rightParen,
-			rightParen,
+		tupleEnd = Mapping(
+			trimmedRune(')'),
 			func(Located[rune]) tupleState {
 				// if ')', then map that to an empty state. This acts as a
 				// sentinel value to indicate "end of tuple".
@@ -133,10 +130,8 @@ var graphSym, value = func() (
 			},
 		)
 
-		rightCurlyBrace = trimmedRune('}')
-		graphEnd        = Mapping(
-			rightCurlyBrace,
-			rightCurlyBrace,
+		graphEnd = Mapping(
+			trimmedRune('}'),
 			func(Located[rune]) graphState {
 				// if '}', then map that to an empty state. This acts as a
 				// sentinel value to indicate "end of graph".
@@ -163,20 +158,21 @@ var graphSym, value = func() (
 		graphOpenEdgeValueTail = new(SymbolPtr[graphState])
 	)
 
-	tuple.Symbol = Reduction[Located[rune], tupleState, *OpenEdge](
-		s("tuple"),
-		trimmedRune('('),
-		tupleTail,
-		func(_ Located[rune], ts tupleState) *OpenEdge {
-			slices.Reverse(ts.ins)
-			return graph.TupleOut(None, ts.ins...)
-		},
+	tuple.Symbol = Named(
+		"tuple",
+		Reduction[Located[rune], tupleState, *OpenEdge](
+			trimmedRune('('),
+			tupleTail,
+			func(_ Located[rune], ts tupleState) *OpenEdge {
+				slices.Reverse(ts.ins)
+				return graph.TupleOut(None, ts.ins...)
+			},
+		),
 	)
 
 	tupleTail.Symbol = FirstOf(
 		tupleEnd,
 		Mapping[tupleState, tupleState](
-			tupleOpenEdge,
 			tupleOpenEdge,
 			func(ts tupleState) tupleState {
 				ts.ins = append(ts.ins, ts.oe)
@@ -188,7 +184,6 @@ var graphSym, value = func() (
 
 	tupleOpenEdge.Symbol = FirstOf(
 		Reduction[Located[Value], tupleState, tupleState](
-			value,
 			value,
 			tupleOpenEdgeValueTail,
 			func(val Located[Value], ts tupleState) tupleState {
@@ -197,7 +192,6 @@ var graphSym, value = func() (
 			},
 		),
 		Reduction[*OpenEdge, tupleState, tupleState](
-			tuple,
 			tuple,
 			tupleOpenEdgeTail,
 			func(oe *OpenEdge, ts tupleState) tupleState {
@@ -217,23 +211,24 @@ var graphSym, value = func() (
 		Prefixed[Located[rune], tupleState](trimmedRune('<'), tupleOpenEdge),
 	)
 
-	graphSym.Symbol = Reduction[Located[rune], graphState, Located[Value]](
-		s("graph"),
-		trimmedRune('{'),
-		graphTail,
-		func(r Located[rune], gs graphState) Located[Value] {
-			if gs.g == nil {
-				gs.g = new(Graph)
-			}
+	graphSym.Symbol = Named(
+		"graph",
+		Reduction[Located[rune], graphState, Located[Value]](
+			trimmedRune('{'),
+			graphTail,
+			func(r Located[rune], gs graphState) Located[Value] {
+				if gs.g == nil {
+					gs.g = new(Graph)
+				}
 
-			return Locate(r.Location, Value{Graph: gs.g})
-		},
+				return Locate(r.Location, Value{Graph: gs.g})
+			},
+		),
 	)
 
 	graphTail.Symbol = FirstOf(
 		graphEnd,
 		Reduction(
-			name,
 			name,
 			Prefixed[Located[rune], graphState](
 				trimmedRune('='), graphOpenEdge,
@@ -253,7 +248,6 @@ var graphSym, value = func() (
 
 	graphOpenEdge.Symbol = FirstOf(
 		Reduction[Located[Value], graphState, graphState](
-			value,
 			value,
 			graphOpenEdgeValueTail,
 			func(val Located[Value], gs graphState) graphState {
@@ -262,7 +256,6 @@ var graphSym, value = func() (
 			},
 		),
 		Reduction[*OpenEdge, graphState, graphState](
-			tuple,
 			tuple,
 			graphOpenEdgeTail,
 			func(oe *OpenEdge, gs graphState) graphState {

gg/decoder_test.go

@@ -41,7 +41,7 @@ func TestDecoder(t *testing.T) {
 	}
 
 	expNum := func(row, col int, n int64) Located[Value] {
-		return Located[Value]{Location{row, col}, Number(n)}
+		return Locate(Location{Row: row, Col: col}, Number(n))
 	}
 
 	runTests(t, "number", number, []test{
@@ -53,11 +53,11 @@ func TestDecoder(t *testing.T) {
 	})
 
 	expName := func(row, col int, name string) Located[Value] {
-		return Located[Value]{Location{row, col}, Name(name)}
+		return Locate(Location{Row: row, Col: col}, Name(name))
 	}
 
 	expGraph := func(row, col int, g *Graph) Located[Value] {
-		return Located[Value]{Location{row, col}, Value{Graph: g}}
+		return Locate(Location{Row: row, Col: col}, Value{Graph: g})
 	}
 
 	runTests(t, "name", name, []test{

gg/grammar/example_test.go

@@ -21,9 +21,9 @@ package:
 <number>          ::= <negative-number> | <positive-number>
 
 <list-el-tail> ::= <element> <list-tail>
-<list-tail> ::= ")" | "," <list-el-tail>
-<list-head> ::= ")" | <list-el-tail>
-<list> ::= "(" <list-head>
+<list-tail>    ::= ")" | "," <list-el-tail>
+<list-head>    ::= ")" | <list-el-tail>
+<list>         ::= "(" <list-head>
 
 <element> ::= <number> | <list>
 ```
@@ -48,19 +48,14 @@ func (e Element) String() string {
 	return fmt.Sprint(e.Number)
 }
 
-func s(str string) fmt.Stringer {
-	return grammar.Stringer{S: str}
-}
-
 var (
 	digit = grammar.RuneFunc(
-		s("digit"), func(r rune) bool { return '0' <= r && r <= '9' },
+		"digit", func(r rune) bool { return '0' <= r && r <= '9' },
 	)
 
 	positiveNumber = grammar.StringFromRunes(grammar.OneOrMore(digit))
 
 	negativeNumber = grammar.Reduction(
-		s("negative-number"),
 		grammar.Rune('-'),
 		positiveNumber,
 		func(
@@ -70,16 +65,18 @@ var (
 		},
 	)
 
-	number = grammar.Mapping(
-		s("number"),
-		grammar.FirstOf(negativeNumber, positiveNumber),
-		func(str grammar.Located[string]) Element {
-			i, err := strconv.ParseInt(str.Value, 10, 64)
-			if err != nil {
-				panic(fmt.Errorf("parsing %q as int: %w", str, err))
-			}
-			return Element{Number: i}
-		},
+	number = grammar.Named(
+		"number",
+		grammar.Mapping(
+			grammar.FirstOf(negativeNumber, positiveNumber),
+			func(str grammar.Located[string]) Element {
+				i, err := strconv.ParseInt(str.Value, 10, 64)
+				if err != nil {
+					panic(fmt.Errorf("parsing %q as int: %w", str, err))
+				}
+				return Element{Number: i}
+			},
+		),
 	)
 
 	// Because the list/element definitions are recursive it requires using
@@ -95,19 +92,13 @@ var (
 			element  = new(grammar.SymbolPtr[Element])
 
 			// Right parenthesis indicates the end of a list, at which point we
-			// can initialize the state which gets returned down the stack. We
-			// pass rightParen as the Stringer because we want that to still be
-			// the string identifier for this branch of the symbol, for error
-			// purposes.
-			rightParen = grammar.Rune(')')
-			listTerm   = grammar.Mapping(
-				rightParen,
-				rightParen,
+			// can initialize the state which gets returned down the stack.
+			listTerm = grammar.Mapping(
+				grammar.Rune(')'),
 				func(grammar.Located[rune]) listState { return listState{} },
 			)
 
 			listElTail = grammar.Reduction[Element, listState, listState](
-				element, // Stringer
 				element,
 				listTail,
 				func(el Element, ls listState) listState {
@@ -124,16 +115,16 @@ var (
 			grammar.Prefixed(grammar.Rune(','), listElTail),
 		)
 
-		list.Symbol = grammar.Reduction[
-			grammar.Located[rune], listState, Element,
-		](
-			s("list"),
-			grammar.Rune('('),
-			listHead,
-			func(_ grammar.Located[rune], ls listState) Element {
-				slices.Reverse(ls)
-				return Element{List: []Element(ls)}
-			},
+		list.Symbol = grammar.Named(
+			"list",
+			grammar.Reduction[grammar.Located[rune], listState, Element](
+				grammar.Rune('('),
+				listHead,
+				func(_ grammar.Located[rune], ls listState) Element {
+					slices.Reverse(ls)
+					return Element{List: []Element(ls)}
+				},
+			),
 		)
 
 		element.Symbol = grammar.FirstOf[Element](number, list)

gg/grammar/symbol.go

@@ -47,11 +47,24 @@ type SymbolPtr[T any] struct {
 	Symbol[T]
 }
 
+func named[T any](stringer fmt.Stringer, sym Symbol[T]) Symbol[T] {
+	return &symbol[T]{
+		stringer,
+		sym.Decode,
+	}
+}
+
+// Named wraps the given Symbol such that its String method returns the given
+// name.
+func Named[T any](name string, sym Symbol[T]) Symbol[T] {
+	return named(Stringer{S: name}, sym)
+}
+
 // RuneFunc matches and produces any rune for which the given function returns
 // true.
-func RuneFunc(stringer fmt.Stringer, fn func(rune) bool) Symbol[Located[rune]] {
+func RuneFunc(name string, fn func(rune) bool) Symbol[Located[rune]] {
 	return &symbol[Located[rune]]{
-		stringer,
+		Stringer{S: name},
 		func(rr Reader) (Located[rune], error) {
 			var zero Located[rune]
 
@@ -75,7 +88,7 @@ func RuneFunc(stringer fmt.Stringer, fn func(rune) bool) Symbol[Located[rune]] {
 // Rune matches and produces the given rune.
 func Rune(r rune) Symbol[Located[rune]] {
 	return RuneFunc(
-		Stringer{S: fmt.Sprintf("'%c'", r)},
+		fmt.Sprintf("'%c'", r),
 		func(r2 rune) bool { return r == r2 },
 	)
 }
@@ -84,7 +97,7 @@ func Rune(r rune) Symbol[Located[rune]] {
 // given Symbol. The slice must not be empty. StringFromRunes does not match if
 // the given Symbol does not match.
 func StringFromRunes(sym Symbol[[]Located[rune]]) Symbol[Located[string]] {
-	return Mapping(sym, sym, func(runes []Located[rune]) Located[string] {
+	return Mapping(sym, func(runes []Located[rune]) Located[string] {
 		if len(runes) == 0 {
 			panic("StringFromRunes used on empty set of runes")
 		}
@@ -101,10 +114,10 @@ func StringFromRunes(sym Symbol[[]Located[rune]]) Symbol[Located[string]] {
 // Symbol and passing it through the given mapping function. If the given Symbol
 // doesn't match then neither does Map.
 func Mapping[Ta, Tb any](
-	stringer fmt.Stringer, sym Symbol[Ta], fn func(Ta) Tb,
+	sym Symbol[Ta], fn func(Ta) Tb,
 ) Symbol[Tb] {
 	return &symbol[Tb]{
-		stringer,
+		sym,
 		func(rr Reader) (Tb, error) {
 			var zero Tb
 			va, err := sym.Decode(rr)
@@ -214,13 +227,12 @@ func FirstOf[T any](syms ...Symbol[T]) Symbol[T] {
 // If symA does not match then Reduction does not match. If symA matches but
 // symB does not then also match then Reduction produces a LocatedError.
 func Reduction[Ta, Tb, Tc any](
-	stringer fmt.Stringer,
 	symA Symbol[Ta],
 	symB Symbol[Tb],
 	fn func(Ta, Tb) Tc,
 ) Symbol[Tc] {
 	return &symbol[Tc]{
-		stringer,
+		symA,
 		func(rr Reader) (Tc, error) {
 			var zero Tc
 
@@ -248,9 +260,9 @@ func Reduction[Ta, Tb, Tc any](
 // If prefixSym does not match then Prefixed does not match. If prefixSym
 // matches but sym does not also match then Prefixed produces a LocatedError.
 func Prefixed[Ta, Tb any](prefixSym Symbol[Ta], sym Symbol[Tb]) Symbol[Tb] {
-	return Reduction(prefixSym, prefixSym, sym, func(_ Ta, b Tb) Tb {
+	return named(prefixSym, Reduction(prefixSym, sym, func(_ Ta, b Tb) Tb {
 		return b
-	})
+	}))
 }
 
 // PrefixDiscarded is similar to Prefixed, except that if sym does not match
@@ -282,13 +294,13 @@ func PrefixDiscarded[Ta, Tb any](prefixSym Symbol[Ta], sym Symbol[Tb]) Symbol[Tb
 // If sym does not match then Suffixed does not match. If sym matches but
 // suffixSym does not also match then Suffixed produces a LocatedError.
 func Suffixed[Ta, Tb any](sym Symbol[Ta], suffixSym Symbol[Tb]) Symbol[Ta] {
-	return Reduction(sym, sym, suffixSym, func(a Ta, _ Tb) Ta {
+	return named(sym, Reduction(sym, suffixSym, func(a Ta, _ Tb) Ta {
 		return a
-	})
+	}))
 }
 
 // Discard matches if the given Symbol does, but discards the value it produces,
 // producing an empty value instead.
 func Discard[T any](sym Symbol[T]) Symbol[struct{}] {
-	return Mapping(sym, sym, func(T) struct{} { return struct{}{} })
+	return Mapping(sym, func(T) struct{} { return struct{}{} })
 }