update book code

eBook/examples/chapter_13/parse/parse.go

@@ -0,0 +1,51 @@
+// parse.go
+package parse
+
+import (
+	"fmt"
+	"strings"
+	"strconv"
+)
+
+// A ParseError indicates an error in converting a word into an integer.
+type ParseError struct {
+        Index int      // The index into the space-separated list of words.
+        Word  string   // The word that generated the parse error.
+        Err error // The raw error that precipitated this error, if any.
+}
+
+// String returns a human-readable error message.
+func (e *ParseError) String() string {
+        return fmt.Sprintf("pkg parse: error parsing %q as int", e.Word)
+}
+
+// Parse parses the space-separated words in in put as integers.
+func Parse(input string) (numbers []int, err error) {
+        defer func() {
+                if r := recover(); r != nil {
+                        var ok bool
+                        err, ok = r.(error)
+                        if !ok {
+                                err = fmt.Errorf("pkg: %v", r)
+                        }
+                }
+        }()
+
+        fields := strings.Fields(input)
+        numbers = fields2numbers(fields)
+        return
+}
+
+func fields2numbers(fields []string) (numbers []int) {
+        if len(fields) == 0 {
+                panic("no words to parse")
+        }
+        for idx, field := range fields {
+                num, err := strconv.Atoi(field)
+                if err != nil {
+                        panic(&ParseError{idx, field, err})
+                }
+                numbers = append(numbers, num)
+        }
+        return
+}