uc parser

From https://www.it.uu.se/katalog/aleji304/CompilersProject/uc.html

_examples/µc/main.go

@@ -0,0 +1,291 @@
+package main
+
+import (
+	"github.com/alecthomas/repr"
+
+	"github.com/alecthomas/participle"
+	"github.com/alecthomas/participle/lexer"
+	"github.com/alecthomas/participle/lexer/stateful"
+)
+
+// https://www.it.uu.se/katalog/aleji304/CompilersProject/uc.html
+//
+// program         ::= topdec_list
+// topdec_list     ::= /empty/ | topdec topdec_list
+// topdec          ::= vardec ";"
+//                  | funtype ident "(" formals ")" funbody
+// vardec          ::= scalardec | arraydec
+// scalardec       ::= typename ident
+// arraydec        ::= typename ident "[" intconst "]"
+// typename        ::= "int" | "char"
+// funtype         ::= typename | "void"
+// funbody         ::= "{" locals stmts "}" | ";"
+// formals         ::= "void" | formal_list
+// formal_list     ::= formaldec | formaldec "," formal_list
+// formaldec       ::= scalardec | typename ident "[" "]"
+// locals          ::= /empty/ | vardec ";" locals
+// stmts           ::= /empty/ | stmt stmts
+// stmt            ::= expr ";"
+//                  | "return" expr ";" | "return" ";"
+//                  | "while" condition stmt
+//                  | "if" condition stmt else_part
+//                  | "{" stmts "}"
+//                  | ";"
+// else_part       ::= /empty/ | "else" stmt
+// condition       ::= "(" expr ")"
+// expr            ::= intconst
+//                  | ident | ident "[" expr "]"
+//                  | unop expr
+//                  | expr binop expr
+//                  | ident "(" actuals ")"
+//                  | "(" expr ")"
+// unop            ::= "-" | "!"
+// binop           ::= "+" | "-" | "*" | "/"
+//                  | "<" | ">" | "<=" | ">=" | "!=" | "=="
+//                  | "&&"
+//                  | "="
+// actuals         ::= /empty/ | expr_list
+// expr_list       ::= expr | expr "," expr_list
+
+type Program struct {
+	Pos lexer.Position
+
+	TopDec []*TopDec `@@*`
+}
+
+type TopDec struct {
+	Pos lexer.Position
+
+	FunDec *FunDec `  @@`
+	VarDec *VarDec `| @@ ";"`
+}
+
+type VarDec struct {
+	Pos lexer.Position
+
+	ArrayDec  *ArrayDec  `  @@`
+	ScalarDec *ScalarDec `| @@`
+}
+
+type ScalarDec struct {
+	Pos lexer.Position
+
+	Type string `@Type`
+	Name string `@Ident`
+}
+
+type ArrayDec struct {
+	Pos  lexer.Position
+	Type string `@Type`
+	Name string `@Ident`
+	Size int    `"[" @Int "]"`
+}
+
+type ReturnStmt struct {
+	Pos lexer.Position
+
+	Result *Expr `"return" @@?`
+}
+
+type WhileStmt struct {
+	Pos lexer.Position
+
+	Condition *Expr `"while" "(" @@ ")"`
+	Body      *Stmt `@@`
+}
+
+type IfStmt struct {
+	Pos lexer.Position
+
+	Condition *Expr `"if" "(" @@ ")"`
+	Body      *Stmt `@@`
+	Else      *Stmt `("else" @@)?`
+}
+
+type Stmts struct {
+	Pos lexer.Position
+
+	Stmts []*Stmt `@@*`
+}
+
+type Stmt struct {
+	Pos lexer.Position
+
+	IfStmt     *IfStmt     `  @@`
+	ReturnStmt *ReturnStmt `| @@`
+	WhileStmt  *WhileStmt  `| @@`
+	Block      *Stmts      `| "{" @@ "}"`
+	Expr       *Expr       `| @@`
+	Empty      bool        `| ";"`
+}
+
+type FunBody struct {
+	Pos lexer.Position
+
+	Locals []*VarDec `(@@ ";")*`
+	Stmts  *Stmts    `@@`
+}
+
+type FunDec struct {
+	Pos lexer.Position
+
+	ReturnType string       `@(Type | "void")`
+	Name       string       `@Ident`
+	Parameters []*Parameter `"(" ((@@ ("," @@)*) | "void") ")"`
+	FunBody    *FunBody     `(";" | "{" @@ "}")`
+}
+
+type Parameter struct {
+	Pos lexer.Position
+
+	Array  *ArrayParameter `  @@`
+	Scalar *ScalarDec      `| @@`
+}
+
+type ArrayParameter struct {
+	Pos lexer.Position
+
+	Type  string `@Type`
+	Ident string `@Ident "[" "]"`
+}
+
+type Expr struct {
+	Pos lexer.Position
+
+	Assignment *Assignment `@@`
+}
+
+type Assignment struct {
+	Pos lexer.Position
+
+	Equality *Equality `@@`
+	Op       string    `( @"="`
+	Next     *Equality `  @@ )?`
+}
+
+type Equality struct {
+	Pos lexer.Position
+
+	Comparison *Comparison `@@`
+	Op         string      `[ @( "!" "=" | "=" "=" )`
+	Next       *Equality   `  @@ ]`
+}
+
+type Comparison struct {
+	Pos lexer.Position
+
+	Addition *Addition   `@@`
+	Op       string      `[ @( ">" | ">" "=" | "<" | "<" "=" )`
+	Next     *Comparison `  @@ ]`
+}
+
+type Addition struct {
+	Pos lexer.Position
+
+	Multiplication *Multiplication `@@`
+	Op             string          `[ @( "-" | "+" )`
+	Next           *Addition       `  @@ ]`
+}
+
+type Multiplication struct {
+	Pos lexer.Position
+
+	Unary *Unary          `@@`
+	Op    string          `[ @( "/" | "*" )`
+	Next  *Multiplication `  @@ ]`
+}
+
+type Unary struct {
+	Pos lexer.Position
+
+	Op      string   `  ( @( "!" | "-" )`
+	Unary   *Unary   `    @@ )`
+	Primary *Primary `| @@`
+}
+
+type Primary struct {
+	Pos lexer.Position
+
+	Number        *int        `  @Int`
+	ArrayIndex    *ArrayIndex `| @@`
+	CallFunc      *CallFunc   `| @@`
+	Ident         string      `| @Ident`
+	SubExpression *Expr       `| "(" @@ ")" `
+}
+
+type ArrayIndex struct {
+	Pos lexer.Position
+
+	Ident string  `@Ident`
+	Index []*Expr `("[" @@ "]")+`
+}
+
+type CallFunc struct {
+	Pos lexer.Position
+
+	Ident string  `@Ident`
+	Index []*Expr `"(" (@@ ("," @@)*)? ")"`
+}
+
+var (
+	lex = lexer.Must(stateful.New(stateful.Rules{
+		"Root": {
+			{"comment", `//.*|/\*.*?\*/`, nil},
+			{"whitespace", `\s+`, nil},
+
+			{"Type", `\b(int|char)\b`, nil},
+			{"Ident", `\b([a-zA-Z_][a-zA-Z0-9_]*)\b`, nil},
+			{"Punct", `[-,()*/+%{};&!=:<>]|\[|\]`, nil},
+			{"Int", `\d+`, nil},
+		},
+	}))
+	intType = lex.Symbols()["Int"]
+	parser  = participle.MustBuild(&Program{},
+		participle.Lexer(lex),
+		participle.UseLookahead(3))
+)
+
+func main() {
+	ast := &Program{}
+	defer func() {
+		repr.Println(ast)
+	}()
+	err := parser.ParseString(`
+/* This is an example uC program. */
+void putint(int i);
+
+int fac(int n)
+{
+    if (n < 2)
+        return n;
+    return n * fac(n - 1);
+}
+
+int sum(int n, int a[])
+{
+    int i;
+    int s;
+
+    i = 0;
+    s = 0;
+    while (i < n) {
+        s = s + a[i];
+        i = i + 1;
+    }
+    return s;
+}
+
+int main(void)
+{
+    int a[2];
+
+    a[0] = fac(5);
+    a[1] = 27;
+    putint(sum(2, a)); // prints 147
+    return 0;
+}
+	`, ast)
+	if err != nil {
+		panic(err)
+	}
+}

lexer/stateful/stateful.go

@@ -256,7 +256,13 @@ func (l *Lexer) Next() (lexer.Token, error) { // nolint: golint
 			}
 		}
 		if match == nil || rule == nil {
-			return lexer.Token{}, participle.Errorf(l.pos, "no match")
+			sample := ""
+			if len(l.data) < 16 {
+				sample = string(l.data)
+			} else {
+				sample = string(l.data[:16]) + "..."
+			}
+			return lexer.Token{}, participle.Errorf(l.pos, "no lexer rules in state %q matched input text %q", parent.name, sample)
 		}
 
 		if rule.Action != nil {

nodes.go

@@ -215,6 +215,11 @@ func (d *disjunction) Parse(ctx *parseContext, parent reflect.Value) (out []refl
 				deepestError = branch.Cursor()
 			}
 		} else if value != nil {
+			bt, _ := branch.Peek(0)
+			ct, _ := ctx.Peek(0)
+			if bt == ct {
+				panic(Errorf(bt.Pos, "branch %s was accepted but did not progress the lexer at %s (%q)", a, bt.Pos, bt.Value))
+			}
 			ctx.Accept(branch)
 			return value, nil
 		}