Proper error messages for shorthands

2 files changed, 24 insertions, 26 deletions

diff --git a/src/eval/func.rs b/src/eval/func.rs
index 6d405ca4..887f7989 100644
--- a/src/eval/func.rs
+++ b/src/eval/func.rs
@@ -162,10 +162,7 @@ impl Args {
     ///
     /// Returns a `missing argument: {what}` error if no positional argument is
     /// left.
-    pub fn expect<T>(&mut self, what: &str) -> TypResult<T>
-    where
-        T: Cast<Spanned<Value>>,
-    {
+    pub fn expect<T: Cast>(&mut self, what: &str) -> TypResult<T> {
         match self.eat()? {
             Some(v) => Ok(v),
             None => bail!(self.span, "missing argument: {}", what),
@@ -173,10 +170,7 @@ impl Args {
     }
 
     /// Consume and cast the first positional argument if there is one.
-    pub fn eat<T>(&mut self) -> TypResult<Option<T>>
-    where
-        T: Cast<Spanned<Value>>,
-    {
+    pub fn eat<T: Cast>(&mut self) -> TypResult<Option<T>> {
         for (i, slot) in self.items.iter().enumerate() {
             if slot.name.is_none() {
                 let value = self.items.remove(i).value;
@@ -188,33 +182,29 @@ impl Args {
     }
 
     /// Find and consume the first castable positional argument.
-    pub fn find<T>(&mut self) -> Option<T>
-    where
-        T: Cast<Spanned<Value>>,
-    {
+    pub fn find<T: Cast>(&mut self) -> TypResult<Option<T>> {
         for (i, slot) in self.items.iter().enumerate() {
             if slot.name.is_none() && T::is(&slot.value) {
                 let value = self.items.remove(i).value;
-                return T::cast(value).ok();
+                let span = value.span;
+                return T::cast(value).at(span).map(Some);
             }
         }
-        None
+        Ok(None)
     }
 
     /// Find and consume all castable positional arguments.
-    pub fn all<T>(&mut self) -> impl Iterator<Item = T> + '_
-    where
-        T: Cast<Spanned<Value>>,
-    {
-        std::iter::from_fn(move || self.find())
+    pub fn all<T: Cast>(&mut self) -> TypResult<Vec<T>> {
+        let mut list = vec![];
+        while let Some(value) = self.find()? {
+            list.push(value);
+        }
+        Ok(list)
     }
 
     /// Cast and remove the value for the given named argument, returning an
     /// error if the conversion fails.
-    pub fn named<T>(&mut self, name: &str) -> TypResult<Option<T>>
-    where
-        T: Cast<Spanned<Value>>,
-    {
+    pub fn named<T: Cast>(&mut self, name: &str) -> TypResult<Option<T>> {
         // We don't quit once we have a match because when multiple matches
         // exist, we want to remove all of them and use the last one.
         let mut i = 0;
@@ -231,6 +221,14 @@ impl Args {
         Ok(found)
     }
 
+    /// Same as named, but with fallback to find.
+    pub fn named_or_find<T: Cast>(&mut self, name: &str) -> TypResult<Option<T>> {
+        match self.named(name)? {
+            Some(value) => Ok(Some(value)),
+            None => self.find(),
+        }
+    }
+
     /// Take out all arguments into a new instance.
     pub fn take(&mut self) -> Self {
         Self {
diff --git a/src/eval/value.rs b/src/eval/value.rs
index 2d37b34f..d1f0be76 100644
--- a/src/eval/value.rs
+++ b/src/eval/value.rs
@@ -284,7 +284,7 @@ pub trait Type {
 }
 
 /// Cast from a value to a specific type.
-pub trait Cast<V>: Sized {
+pub trait Cast<V = Spanned<Value>>: Sized {
     /// Check whether the value is castable to `Self`.
     fn is(value: &V) -> bool;
 
@@ -415,7 +415,7 @@ impl Cast<Value> for Value {
     }
 }
 
-impl<T> Cast<Spanned<Value>> for T
+impl<T> Cast for T
 where
     T: Cast<Value>,
 {
@@ -428,7 +428,7 @@ where
     }
 }
 
-impl<T> Cast<Spanned<Value>> for Spanned<T>
+impl<T> Cast for Spanned<T>
 where
     T: Cast<Value>,
 {