Allow more complicated types of bindings in For and use $ for var bindings

hornbeam_grammar/src/ast.rs

@@ -46,13 +46,19 @@ pub struct IfBlock {
 
 #[derive(Clone, Debug, Eq, PartialEq, Serialize)]
 pub struct ForBlock {
-    pub binding: IStr,
+    pub binding: Binding,
     pub iterable: Expression,
     pub blocks: Vec<Block>,
     pub empty_blocks: Vec<Block>,
     pub loc: Locator,
 }
 
+#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+pub enum Binding {
+    Variable(IStr),
+    Ignore,
+}
+
 #[derive(Clone, Debug, Eq, PartialEq, Serialize)]
 pub struct DefineExpandSlot {
     pub name: IStr,

hornbeam_grammar/src/hornbeam.pest

@@ -185,8 +185,10 @@ MapLiteral = { "{" ~ commaSeparatedKVPairs ~ "}" }
 // As in a let binding or for binding.
 // More options in the future, but for now you just get one identifier and that's it!
 Binding = {
-    Identifier
+    VarBinding | IgnoreBinding
 }
+VarBinding = { "$" ~ Identifier }
+IgnoreBinding = { "_" }
 
 LocalisationIdentifier = @{ ASCII_ALPHA ~ (ASCII_ALPHANUMERIC | "_" | "-")+ }
 ParameterisedLocalisation = { "@" ~ LocalisationIdentifier ~ (!"{" | MapLiteral) }

hornbeam_grammar/src/parser.rs

@@ -1,8 +1,8 @@
 #![allow(non_snake_case)]
 
 use crate::ast::{
-    Block, ComponentElement, DefineExpandSlot, DefineFragment, Expression, ForBlock, HtmlElement,
-    IfBlock, StringExpr, StringPiece, Template,
+    Binding, Block, ComponentElement, DefineExpandSlot, DefineFragment, Expression, ForBlock,
+    HtmlElement, IfBlock, StringExpr, StringPiece, Template,
 };
 use crate::{intern, IStr, Locator};
 use lazy_static::lazy_static;
@@ -374,8 +374,20 @@ impl HornbeamParser {
         }))
     }
 
-    fn Binding(input: Node) -> PCResult<IStr> {
-        Ok(intern(input.as_str()))
+    fn Binding(input: Node) -> PCResult<Binding> {
+        Ok(match_nodes!(input.into_children();
+            [VarBinding(b)] => b,
+            [IgnoreBinding(b)] => b,
+        ))
+    }
+
+    fn VarBinding(input: Node) -> PCResult<Binding> {
+        let str = Self::Identifier(input.into_children().single()?)?;
+        Ok(Binding::Variable(str))
+    }
+
+    fn IgnoreBinding(input: Node) -> PCResult<Binding> {
+        Ok(Binding::Ignore)
     }
 
     fn EmptyForBlock(input: Node) -> PCResult<Vec<Block>> {
@@ -515,8 +527,8 @@ else // peculiar.
     fn for_blocks() {
         assert_yaml_snapshot!(parse_template(
             r#"
-for x in $xs
-    for y in $ys
+for $x in $xs
+    for $y in $ys
         "Woot"
     empty
         "no ys"

hornbeam_grammar/src/snapshots/hornbeam_grammar__parser__tests__for_blocks.snap

@@ -1,27 +1,29 @@
 ---
 source: hornbeam_grammar/src/parser.rs
-expression: "parse_template(r#\"\nfor x in $xs\n    for y in $ys\n        \"Woot\"\n    empty\n        \"no ys\"\nempty\n    \"no xs\"\n    \"#,\n        \"inp\").unwrap()"
+expression: "parse_template(r#\"\nfor $x in $xs\n    for $y in $ys\n        \"Woot\"\n    empty\n        \"no ys\"\nempty\n    \"no xs\"\n    \"#,\n        \"inp\").unwrap()"
 ---
 blocks:
   - ForBlock:
-      binding: x
-      iterator:
+      binding:
+        Variable: x
+      iterable:
         Variable:
           name: xs
           loc:
             filename: inp
             line: 2
-            column: 10
+            column: 11
       blocks:
         - ForBlock:
-            binding: y
-            iterator:
+            binding:
+              Variable: y
+            iterable:
               Variable:
                 name: ys
                 loc:
                   filename: inp
                   line: 3
-                  column: 14
+                  column: 15
             blocks:
               - Text:
                   pieces:

hornbeam_interpreter/src/engine.rs

@@ -3,6 +3,7 @@ use crate::InterpreterError;
 use async_recursion::async_recursion;
 use bevy_reflect::{FromReflect, Reflect, ReflectRef};
 use fluent_templates::lazy_static::lazy_static;
+use hornbeam_grammar::ast::Binding;
 use hornbeam_grammar::Locator;
 use hornbeam_ir::ir::{Expression, Step, StepDef, StringPiece};
 use itertools::Itertools;
@@ -195,12 +196,26 @@ impl<'a, O: OutputSystem + Send, LS: LocalisationSystem + Sync + Send> Interpret
                             self.run_steps(scope_idx, empty_steps).await?;
                         } else {
                             for val in list {
+                                // TODO duplicated code
+                                match binding {
+                                    Binding::Variable(var) => {
                                         self.scopes[scope_idx]
                                             .variables
-                                    .insert(String::from(binding as &str), val);
+                                            .insert(String::from(var as &str), val);
+                                    }
+                                    Binding::Ignore => {}
+                                }
+
                                 self.run_steps(scope_idx, body_steps).await?;
                             }
-                            self.scopes[scope_idx].variables.remove(binding as &str);
+
+                            // TODO duplicated code
+                            match binding {
+                                Binding::Variable(var) => {
+                                    self.scopes[scope_idx].variables.remove(var as &str);
+                                }
+                                Binding::Ignore => {}
+                            }
                         }
                     }
                     Value::Reflective(reflective) => match reflective.reflect_ref() {
@@ -212,13 +227,26 @@ impl<'a, O: OutputSystem + Send, LS: LocalisationSystem + Sync + Send> Interpret
                                     // TODO(performance) I'd like to remove this clone!
                                     //                   Can possibly do so with a Yoke or something...
                                     let val = list.get(idx).expect("checked iter").clone_value();
+                                    // TODO duplicated code
+                                    match binding {
+                                        Binding::Variable(var) => {
                                             self.scopes[scope_idx].variables.insert(
-                                        String::from(binding as &str),
+                                                String::from(var as &str),
                                                 Value::from_reflect(val),
                                             );
+                                        }
+                                        Binding::Ignore => {}
+                                    }
                                     self.run_steps(scope_idx, body_steps).await?;
                                 }
-                                self.scopes[scope_idx].variables.remove(binding as &str);
+
+                                // TODO duplicated code
+                                match binding {
+                                    Binding::Variable(var) => {
+                                        self.scopes[scope_idx].variables.remove(var as &str);
+                                    }
+                                    Binding::Ignore => {}
+                                }
                             }
                         }
                         other => {

hornbeam_ir/src/ir.rs

@@ -1,3 +1,4 @@
+use hornbeam_grammar::ast::Binding;
 pub use hornbeam_grammar::ast::{Expression, StringPiece};
 use hornbeam_grammar::{IStr, Locator};
 use serde::Serialize;
@@ -34,8 +35,7 @@ pub enum StepDef {
     },
     For {
         iterable: Expression,
-        // TODO!
-        binding: IStr,
+        binding: Binding,
         body_steps: Vec<Step>,
         empty_steps: Vec<Step>,
     },