[GitHub] ccollins476ad commented on a change in pull request #122: Code for parsing and evaluating syscfg expressions

[GitBox <gi...@apache.org>]

ccollins476ad commented on a change in pull request #122:     Code for parsing and evaluating syscfg expressions
URL: https://github.com/apache/mynewt-newt/pull/122#discussion_r165224470
 
 

 ##########
 File path: newt/parse/lex.go
 ##########
 @@ -0,0 +1,175 @@
+package parse
+
+import (
+	"fmt"
+	"strings"
+
+	"mynewt.apache.org/newt/util"
+)
+
+type TokenCode int
+
+const (
+	TOKEN_NOT_EQUALS TokenCode = iota
+	TOKEN_NOT
+	TOKEN_EQUALS
+	TOKEN_AND
+	TOKEN_OR
+	TOKEN_XOR
+	TOKEN_LPAREN
+	TOKEN_RPAREN
+	TOKEN_STRING
+	TOKEN_NUMBER
+	TOKEN_IDENT
+)
+
+type Token struct {
+	Code   TokenCode
+	Text   string
+	Offset int
+}
+
+// Returns length of token on success; 0 if no match.
+type LexFn func(s string) (string, int, error)
+
+const delimChars = "!='\"&|^() \t\n"
+
+func lexString(s string, sought string) (string, int, error) {
+	if strings.HasPrefix(s, sought) {
+		return sought, len(sought), nil
+	}
+
+	return "", 0, nil
+}
+
+func lexStringFn(sought string) LexFn {
+	return func(s string) (string, int, error) { return lexString(s, sought) }
+}
+
+func lexLitNumber(s string) (string, int, error) {
+	var sub string
+	idx := strings.IndexAny(s, delimChars)
+	if idx == -1 {
+		sub = s
+	} else {
+		sub = s[:idx]
+	}
+	if _, ok := util.AtoiNoOctTry(sub); ok {
+		return sub, len(sub), nil
+	}
+
+	return "", 0, nil
+}
+
+func lexLitString(s string) (string, int, error) {
+	if s[0] != '"' {
+		return "", 0, nil
+	}
+
+	quote2 := strings.IndexByte(s[1:], '"')
+	if quote2 == -1 {
+		return "", 0, fmt.Errorf("unterminated quote: %s", s)
+	}
+
+	return s[1 : quote2+1], quote2 + 2, nil
+}
+
+func lexIdent(s string) (string, int, error) {
+	idx := strings.IndexAny(s, delimChars)
+	if idx == -1 {
+		return s, len(s), nil
+	} else {
+		return s[:idx], idx, nil
+	}
+}
+
+type lexEntry struct {
+	code TokenCode
+	fn   LexFn
+}
+
+var lexEntries = []lexEntry{
 
 Review comment:
   @utzig - Thanks, you are correct.  Originally I planned on using the single character forms for those operators, but I figured most users would be in the "C mindset", so I changed it.
   
   Unfortunately I can't fix the commit message since the PR has already been merged.  However, I will fix the comment in the code and file a new PR.

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