[honu] add string comparison. add test.xml file for linq example

collects/honu/core/main.rkt

@@ -37,6 +37,7 @@
                      [honu-map map]
                      [honu-flow \|]
                      [honu-dot |.|]
+                     [honu-string=? string_equal]
                      [honu-cons ::]
                      [honu-and and] [honu-and &&]
                      [honu-or or] [honu-or \|\|]

collects/honu/core/private/honu2.rkt

@@ -170,6 +170,7 @@
 (define-binary-operator honu-or 0.5 'left or)
 (define-binary-operator honu-cons 0.1 'right cons)
 (define-binary-operator honu-map 0.09 'left map)
+(define-binary-operator honu-string=? 1 'left string=?)
 
 (define-unary-operator honu-not 0.7 'left not)
 

collects/honu/main.rkt

@@ -22,8 +22,10 @@
          null
          null?
          length
+         substring
          (rename-out [honu-cond cond]
                      [null empty]
+                     [string-length string_length]
                      [racket:empty? empty?]
                      [racket:first first]
                      [racket:rest rest]))

collects/tests/honu/linq.honu

@@ -30,6 +30,10 @@ loadXml(file){
   }
 }
 
+starts_with(start, what){
+  substring(what, 0, string_length(start)) string_equal start
+}
+
 var xml = loadXml("test.xml");
 printf("xml ~a\n", xml);
 printf("data: ~a\n", xml.getData());
@@ -48,3 +52,11 @@ printf("addresses ~a\n", addresses);
 for add in addresses do {
   printf("name ~a address ~a\n", add.name, add.address);
 }
+
+printf("+++\n");
+for xs in linq from foo in xml.Descendants("Table1")
+                where starts_with("x", foo.Element("familyName").Value())
+                select foo.Element("familyName").Value() do {
+  printf("only x: ~a\n", xs)
+}
+// printf("---\n");

collects/tests/honu/test.xml

@@ -0,0 +1,22 @@
+<root>
+    <Table1>
+        <ID>3</ID>
+        <familyName>x1</familyName>
+        <address>xa</address>
+    </Table1>
+    <Table1>
+        <ID>4</ID>
+        <familyName>y1</familyName>
+        <address>ya</address>
+    </Table1>
+    <Table1>
+        <ID>5</ID>
+        <familyName>hub</familyName>
+        <address>away</address>
+    </Table1>
+    <Table1>
+        <ID>5</ID>
+        <familyName>xeno</familyName>
+        <address>banana</address>
+    </Table1>
+</root>