improve compiler to abort with error if query is missing

cli/test.yaml

@@ -1,22 +1,36 @@
 - name: empty input
+  args:
+    - '.'
   input: ''
   expected: ''
 
-- name: empty query
+- name: empty args
+  input: 'null'
+  expected: |
+    null
+
+- name: missing query
   args:
     - ''
-  input: '128'
+  error: |
+    compile error: missing query (try ".")
+  exit_code: 3
+
+- name: query with comment
+  args:
+    - '. # comment'
+  input: 'null'
   expected: |
-    128
+    null
 
-- name: comment only query
+- name: missing query with comment
   args:
     - '# comment'
-  input: '128'
-  expected: |
-    128
+  error: |
+    compile error: missing query (try ".")
+  exit_code: 3
 
-- name: query with comment
+- name: query with comment with newline
   args:
     - |
       # comment
@@ -2574,6 +2588,13 @@
             ^  unexpected token "$f"
   exit_code: 3
 
+- name: function declaration without query
+  args:
+    - 'def f: 0;'
+  error: |
+    compile error: missing query (try ".")
+  exit_code: 3
+
 - name: add, subtract, multiply, divide, modulo numbers
   args:
     - -c

compiler.go

@@ -398,6 +398,8 @@ func (c *compiler) compileQuery(e *Query) error {
 		return c.compileTerm(e.Term)
 	}
 	switch e.Op {
+	case Operator(0):
+		return errors.New(`missing query (try ".")`)
 	case OpPipe:
 		if err := c.compileQuery(e.Left); err != nil {
 			return err

parser.go.y

@@ -102,7 +102,7 @@ meta
 body
     : funcdefs
     {
-        $$ = &Query{FuncDefs: reverseFuncDef($1.([]*FuncDef)), Term: &Term{Type: TermTypeIdentity}}
+        $$ = &Query{FuncDefs: reverseFuncDef($1.([]*FuncDef))}
     }
     | query