Add create support to planner

src/backend/gram.rs

@@ -45,6 +45,9 @@ impl GramBackend {
                 next_rel_index: 0,
                 state: ExpandState::NextNode
             })),
+            LogicalPlan::Create { .. } => {
+                panic!("The gram backend does not yet support CREATE statements")
+            }
             LogicalPlan::Return { src, projections } => {
                 let mut converted_projections = Vec::new();
                 for projection in projections {
@@ -65,6 +68,7 @@ impl GramBackend {
             frontend::Expr::Lit(v) => Expr::Lit(v),
             frontend::Expr::Prop(e, props) => Expr::Prop(Box::new(self.convert_expr(*e)), props),
             frontend::Expr::Slot(s) => Expr::Slot(s),
+            _ => panic!("The gram backend does not support this expression type yet: {:?}", expr)
         }
     }
 }
@@ -120,7 +124,7 @@ struct Context {
 }
 
 #[derive(Debug, Clone)]
-pub enum Expr {
+enum Expr {
     Lit(Val),
     // Lookup a property by id
     Prop(Box<Expr>, Vec<Token>),

src/backend/mod.rs

@@ -40,6 +40,9 @@ pub struct Tokens {
 }
 
 impl Tokens {
+    pub fn new() -> Tokens {
+        Tokens{ table: Default::default() }
+    }
     pub fn lookup(&self, tok: usize) -> Option<&str> {
         for (content, candidate) in self.table.iter() {
             if *candidate == tok {

src/cypher.pest

@@ -24,8 +24,10 @@ map_pair = { id ~ ":" ~ expr }
 node = { "(" ~ id? ~ ( ":" ~ label )? ~ map? ~ ")" }
 label = { id }
 
-rel = { "<"? ~ "-" ~ ( "[" ~ id? ~ ( ":" ~ rel_type )? ~ map? ~ "]" )? ~ "-" ~ ">"? }
+rel = { left_arrow? ~ "-" ~ ( "[" ~ id? ~ ( ":" ~ rel_type )? ~ map? ~ "]" )? ~ "-" ~ right_arrow? }
 rel_type = { id }
+left_arrow = { "<" }
+right_arrow = { ">" }
 
 pattern = { node  ~ ( rel ~ node )* }