Allow custom & union productions (#233)

Implements #229

_examples/expr3/main.go

@@ -0,0 +1,134 @@
+package main
+
+import (
+	"strings"
+
+	"github.com/alecthomas/kong"
+	"github.com/alecthomas/participle/v2"
+	"github.com/alecthomas/repr"
+)
+
+type (
+	ExprString struct {
+		Value string `@String`
+	}
+
+	ExprNumber struct {
+		Value float64 `@Int | @Float`
+	}
+
+	ExprIdent struct {
+		Name string `@Ident`
+	}
+
+	ExprParens struct {
+		Inner ExprPrecAll `"(" @@ ")"`
+	}
+
+	ExprUnary struct {
+		Op   string      `@("-" | "!")`
+		Expr ExprOperand `@@`
+	}
+
+	ExprAddSub struct {
+		Head ExprPrec2       `@@`
+		Tail []ExprAddSubExt `@@+`
+	}
+
+	ExprAddSubExt struct {
+		Op   string    `@("+" | "-")`
+		Expr ExprPrec2 `@@`
+	}
+
+	ExprMulDiv struct {
+		Head ExprPrec3       `@@`
+		Tail []ExprMulDivExt `@@+`
+	}
+
+	ExprMulDivExt struct {
+		Op   string    `@("*" | "/")`
+		Expr ExprPrec3 `@@`
+	}
+
+	ExprRem struct {
+		Head ExprOperand  `@@`
+		Tail []ExprRemExt `@@+`
+	}
+
+	ExprRemExt struct {
+		Op   string      `@"%"`
+		Expr ExprOperand `@@`
+	}
+
+	ExprPrecAll interface{ exprPrecAll() }
+	ExprPrec2   interface{ exprPrec2() }
+	ExprPrec3   interface{ exprPrec3() }
+	ExprOperand interface{ exprOperand() }
+)
+
+// These expression types can be matches as individual operands
+func (ExprIdent) exprOperand()  {}
+func (ExprNumber) exprOperand() {}
+func (ExprString) exprOperand() {}
+func (ExprParens) exprOperand() {}
+func (ExprUnary) exprOperand()  {}
+
+// These expression types can be matched at precedence level 3
+func (ExprIdent) exprPrec3()  {}
+func (ExprNumber) exprPrec3() {}
+func (ExprString) exprPrec3() {}
+func (ExprParens) exprPrec3() {}
+func (ExprUnary) exprPrec3()  {}
+func (ExprRem) exprPrec3()    {}
+
+// These expression types can be matched at precedence level 2
+func (ExprIdent) exprPrec2()  {}
+func (ExprNumber) exprPrec2() {}
+func (ExprString) exprPrec2() {}
+func (ExprParens) exprPrec2() {}
+func (ExprUnary) exprPrec2()  {}
+func (ExprRem) exprPrec2()    {}
+func (ExprMulDiv) exprPrec2() {}
+
+// These expression types can be matched at the minimum precedence level
+func (ExprIdent) exprPrecAll()  {}
+func (ExprNumber) exprPrecAll() {}
+func (ExprString) exprPrecAll() {}
+func (ExprParens) exprPrecAll() {}
+func (ExprUnary) exprPrecAll()  {}
+func (ExprRem) exprPrecAll()    {}
+func (ExprMulDiv) exprPrecAll() {}
+func (ExprAddSub) exprPrecAll() {}
+
+type Expression struct {
+	X ExprPrecAll `@@`
+}
+
+var parser = participle.MustBuild(&Expression{},
+	// This grammar requires enough lookahead to see the entire expression before
+	// it can select the proper binary expression type - in other words, we only
+	// know that `1 * 2 * 3 * 4` isn't the left-hand side of an addition or subtraction
+	// expression until we know for sure that no `+` or `-` operator follows it
+	participle.UseLookahead(99999),
+	// Register the ExprOperand union so we can parse individual operands
+	participle.ParseUnion[ExprOperand](ExprUnary{}, ExprIdent{}, ExprNumber{}, ExprString{}, ExprParens{}),
+	// Register the ExprPrec3 union so we can parse expressions at precedence level 3
+	participle.ParseUnion[ExprPrec3](ExprRem{}, ExprUnary{}, ExprIdent{}, ExprNumber{}, ExprString{}, ExprParens{}),
+	// Register the ExprPrec2 union so we can parse expressions at precedence level 2
+	participle.ParseUnion[ExprPrec2](ExprMulDiv{}, ExprRem{}, ExprUnary{}, ExprIdent{}, ExprNumber{}, ExprString{}, ExprParens{}),
+	// Register the ExprPrecAll union so we can parse expressions at the minimum precedence level
+	participle.ParseUnion[ExprPrecAll](ExprAddSub{}, ExprMulDiv{}, ExprRem{}, ExprUnary{}, ExprIdent{}, ExprNumber{}, ExprString{}, ExprParens{}),
+)
+
+func main() {
+	var cli struct {
+		Expr []string `arg required help:"Expression to parse."`
+	}
+	ctx := kong.Parse(&cli)
+
+	expr := &Expression{}
+	err := parser.ParseString("", strings.Join(cli.Expr, " "), expr)
+	ctx.FatalIfErrorf(err)
+
+	repr.Println(expr)
+}

_examples/expr3/main_test.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"testing"
+
+	require "github.com/alecthomas/assert/v2"
+)
+
+func TestExpressionParser(t *testing.T) {
+	type testCase struct {
+		src      string
+		expected ExprPrecAll
+	}
+
+	for _, c := range []testCase{
+		{`1`, ExprNumber{1}},
+		{`1.5`, ExprNumber{1.5}},
+		{`"a"`, ExprString{`"a"`}},
+		{`(1)`, ExprParens{ExprNumber{1}}},
+		{`1 + 1`, ExprAddSub{ExprNumber{1}, []ExprAddSubExt{{"+", ExprNumber{1}}}}},
+		{`1 - 1`, ExprAddSub{ExprNumber{1}, []ExprAddSubExt{{"-", ExprNumber{1}}}}},
+		{`1 * 1`, ExprMulDiv{ExprNumber{1}, []ExprMulDivExt{{"*", ExprNumber{1}}}}},
+		{`1 / 1`, ExprMulDiv{ExprNumber{1}, []ExprMulDivExt{{"/", ExprNumber{1}}}}},
+		{`1 % 1`, ExprRem{ExprNumber{1}, []ExprRemExt{{"%", ExprNumber{1}}}}},
+		{
+			`a + b - c * d / e % f`,
+			ExprAddSub{
+				ExprIdent{"a"},
+				[]ExprAddSubExt{
+					{"+", ExprIdent{"b"}},
+					{"-", ExprMulDiv{
+						ExprIdent{"c"},
+						[]ExprMulDivExt{
+							{"*", ExprIdent{Name: "d"}},
+							{"/", ExprRem{
+								ExprIdent{"e"},
+								[]ExprRemExt{{"%", ExprIdent{"f"}}},
+							}},
+						},
+					}},
+				},
+			},
+		},
+	} {
+		var actual Expression
+		require.NoError(t, parser.ParseString("<test>", c.src, &actual))
+		require.Equal(t, c.expected, actual.X)
+	}
+}

_examples/expr4/main.go

@@ -0,0 +1,136 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+	"text/scanner"
+
+	"github.com/alecthomas/kong"
+	"github.com/alecthomas/participle/v2"
+	"github.com/alecthomas/participle/v2/lexer"
+	"github.com/alecthomas/repr"
+)
+
+type operatorPrec struct{ Left, Right int }
+
+var operatorPrecs = map[string]operatorPrec{
+	"+": {1, 1},
+	"-": {1, 1},
+	"*": {3, 2},
+	"/": {5, 4},
+	"%": {7, 6},
+}
+
+type (
+	Expr interface{ expr() }
+
+	ExprIdent  struct{ Name string }
+	ExprString struct{ Value string }
+	ExprNumber struct{ Value float64 }
+	ExprParens struct{ Sub Expr }
+
+	ExprUnary struct {
+		Op  string
+		Sub Expr
+	}
+
+	ExprBinary struct {
+		Lhs Expr
+		Op  string
+		Rhs Expr
+	}
+)
+
+func (ExprIdent) expr()  {}
+func (ExprString) expr() {}
+func (ExprNumber) expr() {}
+func (ExprParens) expr() {}
+func (ExprUnary) expr()  {}
+func (ExprBinary) expr() {}
+
+func parseExprAny(lex *lexer.PeekingLexer) (Expr, error) { return parseExprPrec(lex, 0) }
+
+func parseExprAtom(lex *lexer.PeekingLexer) (Expr, error) {
+	switch peek := lex.Peek(); {
+	case peek.Type == scanner.Ident:
+		return ExprIdent{lex.Next().Value}, nil
+	case peek.Type == scanner.String:
+		val, err := strconv.Unquote(lex.Next().Value)
+		if err != nil {
+			return nil, err
+		}
+		return ExprString{val}, nil
+	case peek.Type == scanner.Int || peek.Type == scanner.Float:
+		val, err := strconv.ParseFloat(lex.Next().Value, 64)
+		if err != nil {
+			return nil, err
+		}
+		return ExprNumber{val}, nil
+	case peek.Value == "(":
+		_ = lex.Next()
+		inner, err := parseExprAny(lex)
+		if err != nil {
+			return nil, err
+		}
+		if lex.Peek().Value != ")" {
+			return nil, fmt.Errorf("expected closing ')'")
+		}
+		_ = lex.Next()
+		return ExprParens{inner}, nil
+	default:
+		return nil, participle.NextMatch
+	}
+}
+
+func parseExprPrec(lex *lexer.PeekingLexer, minPrec int) (Expr, error) {
+	var lhs Expr
+	if peeked := lex.Peek(); peeked.Value == "-" || peeked.Value == "!" {
+		op := lex.Next().Value
+		atom, err := parseExprAtom(lex)
+		if err != nil {
+			return nil, err
+		}
+		lhs = ExprUnary{op, atom}
+	} else {
+		atom, err := parseExprAtom(lex)
+		if err != nil {
+			return nil, err
+		}
+		lhs = atom
+	}
+
+	for {
+		peek := lex.Peek()
+		prec, isOp := operatorPrecs[peek.Value]
+		if !isOp || prec.Left < minPrec {
+			break
+		}
+		op := lex.Next().Value
+		rhs, err := parseExprPrec(lex, prec.Right)
+		if err != nil {
+			return nil, err
+		}
+		lhs = ExprBinary{lhs, op, rhs}
+	}
+	return lhs, nil
+}
+
+type Expression struct {
+	X Expr `@@`
+}
+
+var parser = participle.MustBuild(&Expression{}, participle.ParseTypeWith(parseExprAny))
+
+func main() {
+	var cli struct {
+		Expr []string `arg required help:"Expression to parse."`
+	}
+	ctx := kong.Parse(&cli)
+
+	expr := &Expression{}
+	err := parser.ParseString("", strings.Join(cli.Expr, " "), expr)
+	ctx.FatalIfErrorf(err)
+
+	repr.Println(expr)
+}

_examples/expr4/main_test.go

@@ -0,0 +1,61 @@
+package main
+
+import (
+	"testing"
+
+	require "github.com/alecthomas/assert/v2"
+)
+
+func TestCustomExprParser(t *testing.T) {
+	type testCase struct {
+		src      string
+		expected Expr
+	}
+
+	for _, c := range []testCase{
+		{`1`, ExprNumber{1}},
+		{`1.5`, ExprNumber{1.5}},
+		{`"a"`, ExprString{"a"}},
+		{`(1)`, ExprParens{ExprNumber{1}}},
+		{`1+1`, ExprBinary{ExprNumber{1}, "+", ExprNumber{1}}},
+		{`1-1`, ExprBinary{ExprNumber{1}, "-", ExprNumber{1}}},
+		{`1*1`, ExprBinary{ExprNumber{1}, "*", ExprNumber{1}}},
+		{`1/1`, ExprBinary{ExprNumber{1}, "/", ExprNumber{1}}},
+		{`1%1`, ExprBinary{ExprNumber{1}, "%", ExprNumber{1}}},
+		{`a - -b`, ExprBinary{ExprIdent{"a"}, "-", ExprUnary{"-", ExprIdent{"b"}}}},
+		{
+			`a + b - c * d / e % f`,
+			ExprBinary{
+				ExprIdent{"a"}, "+", ExprBinary{
+					ExprIdent{"b"}, "-", ExprBinary{
+						ExprIdent{"c"}, "*", ExprBinary{
+							ExprIdent{"d"}, "/", ExprBinary{
+								ExprIdent{"e"}, "%", ExprIdent{"f"},
+							},
+						},
+					},
+				},
+			},
+		},
+		{
+			`a * b + c * d`,
+			ExprBinary{
+				ExprBinary{ExprIdent{"a"}, "*", ExprIdent{"b"}},
+				"+",
+				ExprBinary{ExprIdent{"c"}, "*", ExprIdent{"d"}},
+			},
+		},
+		{
+			`(a + b) * (c + d)`,
+			ExprBinary{
+				ExprParens{ExprBinary{ExprIdent{"a"}, "+", ExprIdent{"b"}}},
+				"*",
+				ExprParens{ExprBinary{ExprIdent{"c"}, "+", ExprIdent{"d"}}},
+			},
+		},
+	} {
+		var actual Expression
+		require.NoError(t, parser.ParseString("", c.src, &actual))
+		require.Equal(t, c.expected, actual.X)
+	}
+}