4 files changed, 52 insertions(+), 0 deletions(-)

M go.mod
A go.sum
M internal/bootstrap/token/token.go
A internal/bootstrap/token/token_test.go

@@ 1,3 1,5 @@
 module git.sr.ht/~mna/fastpeg
 
 go 1.12
+
+require github.com/stretchr/testify v1.3.0

@@ 0,0 1,7 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.3.0 h1:TivCn/peBQ7UY8ooIcPgZFpTNSz0Q2U6UrFlUfqbe0Q=
+github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=

@@ 88,11 88,31 @@ var stringTokens = [...]string{
 	Rparen:        ")",
 }
 
+var reverseToken map[string]Token
+
+func init() {
+	reverseToken = make(map[string]Token, len(stringTokens))
+	for t, s := range stringTokens {
+		if s != "" {
+			reverseToken[s] = Token(t)
+		}
+	}
+}
+
 // IsLiteral returns true if token t is an identifier or a literal.
 func (t Token) IsLiteral() bool {
 	return t > litStart && t < litEnd
 }
 
+// FromString returns the token that has a string representation of s.
+func FromString(s string) Token {
+	t, ok := reverseToken[s]
+	if !ok {
+		t = Illegal
+	}
+	return t
+}
+
 // String returns the string representation of token t.
 func (t Token) String() string {
 	var s string

@@ 0,0 1,23 @@
+package token
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestStringReverse(t *testing.T) {
+	// <= symEnd to test beyond the last token
+	for tk := Illegal; tk <= symEnd; tk++ {
+		t.Run(tk.String(), func(t *testing.T) {
+			s := tk.String()
+			rev := FromString(s)
+			if strings.HasPrefix(s, "token(") {
+				require.Equal(t, Illegal, rev)
+			} else {
+				require.Equal(t, tk, rev)
+			}
+		})
+	}
+}