1 files changed, 83 insertions, 0 deletions
diff --git a/src/syntax/scope.rs b/src/syntax/scope.rs
new file mode 100644
index 00000000..2aae331d
--- /dev/null
+++ b/src/syntax/scope.rs
@@ -0,0 +1,83 @@
+use std::collections::HashMap;
+use std::fmt::{self, Debug, Formatter};
+
+use crate::func::ParseFunc;
+use super::func::FuncHeader;
+use super::parsing::{ParseContext, Parsed};
+use super::span::Spanned;
+use super::Model;
+
+
+/// A map from identifiers to function parsers.
+pub struct Scope {
+    parsers: HashMap<String, Box<Parser>>,
+    fallback: Box<Parser>
+}
+
+impl Scope {
+    /// Create a new empty scope with a fallback parser that is invoked when no
+    /// match is found.
+    pub fn new<F>() -> Scope
+    where F: ParseFunc<Meta=()> + Model + 'static {
+        Scope {
+            parsers: HashMap::new(),
+            fallback: parser::<F>(()),
+        }
+    }
+
+    /// Create a new scope with the standard functions contained.
+    pub fn with_std() -> Scope {
+        crate::library::std()
+    }
+
+    /// Associate the given name with a type that is parseable into a function.
+    pub fn add<F>(&mut self, name: &str)
+    where F: ParseFunc<Meta=()> + Model + 'static {
+        self.add_with_meta::<F>(name, ());
+    }
+
+    /// Add a parseable type with additional metadata  that is given to the
+    /// parser (other than the default of `()`).
+    pub fn add_with_meta<F>(&mut self, name: &str, metadata: <F as ParseFunc>::Meta)
+    where F: ParseFunc + Model + 'static {
+        self.parsers.insert(
+            name.to_owned(),
+            parser::<F>(metadata),
+        );
+    }
+
+    /// Return the parser with the given name if there is one.
+    pub fn get_parser(&self, name: &str) -> Result<&Parser, &Parser> {
+        self.parsers.get(name)
+            .map(|x| &**x)
+            .ok_or_else(|| &*self.fallback)
+    }
+
+    /// Return the fallback parser.
+    pub fn get_fallback_parser(&self) -> &Parser {
+        &*self.fallback
+    }
+}
+
+impl Debug for Scope {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "Scope ")?;
+        write!(f, "{:?}", self.parsers.keys())
+    }
+}
+
+/// A function which parses the source of a function into a model type which
+/// implements [`Model`].
+type Parser = dyn Fn(
+    FuncHeader,
+    Option<Spanned<&str>>,
+    ParseContext,
+) -> Parsed<Box<dyn Model>>;
+
+fn parser<F>(metadata: <F as ParseFunc>::Meta) -> Box<Parser>
+where F: ParseFunc + Model + 'static {
+    Box::new(move |h, b, c| {
+        F::parse(h, b, c, metadata.clone())
+            .map(|model| Box::new(model) as Box<dyn Model>)
+    })
+}