Remove classes and improve naming

1 files changed, 202 insertions, 0 deletions

diff --git a/src/eval/args.rs b/src/eval/args.rs
new file mode 100644
index 00000000..67da9865
--- /dev/null
+++ b/src/eval/args.rs
@@ -0,0 +1,202 @@
+use std::fmt::{self, Debug, Formatter, Write};
+
+use super::{Cast, Value};
+use crate::diag::{At, TypResult};
+use crate::syntax::{Span, Spanned};
+use crate::util::EcoString;
+
+/// Evaluated arguments to a function.
+#[derive(Clone, PartialEq, Hash)]
+pub struct Args {
+    /// The span of the whole argument list.
+    pub span: Span,
+    /// The positional and named arguments.
+    pub items: Vec<Arg>,
+}
+
+/// An argument to a function call: `12` or `draw: false`.
+#[derive(Clone, PartialEq, Hash)]
+pub struct Arg {
+    /// The span of the whole argument.
+    pub span: Span,
+    /// The name of the argument (`None` for positional arguments).
+    pub name: Option<EcoString>,
+    /// The value of the argument.
+    pub value: Spanned<Value>,
+}
+
+impl Args {
+    /// Create positional arguments from a span and values.
+    pub fn from_values(span: Span, values: impl IntoIterator<Item = Value>) -> Self {
+        Self {
+            span,
+            items: values
+                .into_iter()
+                .map(|value| Arg {
+                    span,
+                    name: None,
+                    value: Spanned::new(value, span),
+                })
+                .collect(),
+        }
+    }
+
+    /// Consume and cast the first positional argument.
+    ///
+    /// 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>>,
+    {
+        match self.eat()? {
+            Some(v) => Ok(v),
+            None => bail!(self.span, "missing argument: {}", what),
+        }
+    }
+
+    /// 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>>,
+    {
+        for (i, slot) in self.items.iter().enumerate() {
+            if slot.name.is_none() {
+                let value = self.items.remove(i).value;
+                let span = value.span;
+                return T::cast(value).at(span).map(Some);
+            }
+        }
+        Ok(None)
+    }
+
+    /// Find and consume the first castable positional argument.
+    pub fn find<T>(&mut self) -> TypResult<Option<T>>
+    where
+        T: Cast<Spanned<Value>>,
+    {
+        for (i, slot) in self.items.iter().enumerate() {
+            if slot.name.is_none() && T::is(&slot.value) {
+                let value = self.items.remove(i).value;
+                let span = value.span;
+                return T::cast(value).at(span).map(Some);
+            }
+        }
+        Ok(None)
+    }
+
+    /// Find and consume all castable positional arguments.
+    pub fn all<T>(&mut self) -> TypResult<Vec<T>>
+    where
+        T: Cast<Spanned<Value>>,
+    {
+        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>>,
+    {
+        // 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;
+        let mut found = None;
+        while i < self.items.len() {
+            if self.items[i].name.as_deref() == Some(name) {
+                let value = self.items.remove(i).value;
+                let span = value.span;
+                found = Some(T::cast(value).at(span)?);
+            } else {
+                i += 1;
+            }
+        }
+        Ok(found)
+    }
+
+    /// Same as named, but with fallback to find.
+    pub fn named_or_find<T>(&mut self, name: &str) -> TypResult<Option<T>>
+    where
+        T: Cast<Spanned<Value>>,
+    {
+        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 {
+            span: self.span,
+            items: std::mem::take(&mut self.items),
+        }
+    }
+
+    /// Return an "unexpected argument" error if there is any remaining
+    /// argument.
+    pub fn finish(self) -> TypResult<()> {
+        if let Some(arg) = self.items.first() {
+            bail!(arg.span, "unexpected argument");
+        }
+        Ok(())
+    }
+
+    /// Reinterpret these arguments as actually being an array index.
+    pub fn into_index(self) -> TypResult<i64> {
+        self.into_castable("index")
+    }
+
+    /// Reinterpret these arguments as actually being a dictionary key.
+    pub fn into_key(self) -> TypResult<EcoString> {
+        self.into_castable("key")
+    }
+
+    /// Reinterpret these arguments as actually being a single castable thing.
+    fn into_castable<T: Cast>(self, what: &str) -> TypResult<T> {
+        let mut iter = self.items.into_iter();
+        let value = match iter.next() {
+            Some(Arg { name: None, value, .. }) => value.v.cast().at(value.span)?,
+            None => {
+                bail!(self.span, "missing {}", what);
+            }
+            Some(Arg { name: Some(_), span, .. }) => {
+                bail!(span, "named pair is not allowed here");
+            }
+        };
+
+        if let Some(arg) = iter.next() {
+            bail!(arg.span, "only one {} is allowed", what);
+        }
+
+        Ok(value)
+    }
+}
+
+impl Debug for Args {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        f.write_char('(')?;
+        for (i, arg) in self.items.iter().enumerate() {
+            arg.fmt(f)?;
+            if i + 1 < self.items.len() {
+                f.write_str(", ")?;
+            }
+        }
+        f.write_char(')')
+    }
+}
+
+impl Debug for Arg {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        if let Some(name) = &self.name {
+            f.write_str(name)?;
+            f.write_str(": ")?;
+        }
+        Debug::fmt(&self.value.v, f)
+    }
+}