1 files changed, 102 insertions, 0 deletions
diff --git a/src/type/case.rs b/src/type/case.rs
new file mode 100644
index 0000000..2403acd
--- /dev/null
+++ b/src/type/case.rs
@@ -0,0 +1,102 @@
+
+use crate::r#type::{Type, TypeError, Type::*, TypeError::*, PatFail::*, util::*};
+use crate::sexp::{SExp, SExp::*, SLeaf::*, util::*};
+
+impl SExp {
+
+    /// Checks if this expression matches the given type,
+    /// returns all variable names bound by a respective case.
+    ///
+    /// Two equal values match:
+    /// ```rust
+    /// use myslip::sexp::{SExp::*, SLeaf::*, util::*};
+    /// use myslip::r#type::{Type::*, util::*, TypeError::*, PatFail::*};
+    /// assert_eq!(
+    ///     scons(1, scons(2, Nil))
+    ///         .matches_type(&List(vec![Integer, Integer])),
+    ///     Ok(vec![])
+    /// );
+    /// ```
+    ///
+    /// On the other hand, if values don't match, an invalid pattern
+    /// error should be thrown:
+    /// ```rust
+    /// use myslip::sexp::{SExp::*, SLeaf::*, util::*};
+    /// use myslip::r#type::{Type::*, util::*, TypeError::*, PatFail::*};
+    /// assert_eq!(
+    ///     scons(1, scons(2, Nil))
+    ///         .matches_type(&List(vec![Integer])),
+    ///     Err(InvalidPattern(TypeMismatch {
+    ///         pattern: scons(1, scons(2, Nil)),
+    ///         expected: List(vec![Integer]),
+    ///         found: List(vec![Integer, Integer])
+    ///     }))
+    /// );
+    /// ```
+    ///
+    /// A wildcard variable matches too and gets the correct type:
+    /// ```rust
+    /// use myslip::sexp::{SExp::*, SLeaf::*, util::*};
+    /// use myslip::r#type::{Type::*, util::*, TypeError::*, PatFail::*};
+    /// assert_eq!(
+    ///     var("x").matches_type(&List(vec![Integer, Integer])),
+    ///     Ok(vec![("x".to_string(), List(vec![Integer, Integer]))])
+    /// );
+    /// ```
+    ///
+    /// Obviously that should also work for sub-expressions:
+    /// ```rust
+    /// use myslip::sexp::{SExp::*, SLeaf::*, util::*};
+    /// use myslip::r#type::{Type::*, util::*, TypeError::*, PatFail::*};
+    /// assert_eq!(
+    ///     scons(var("x"), scons(2, Nil)).matches_type(&List(vec![arr(Integer, Integer), Integer])),
+    ///     Ok(vec![("x".to_string(), arr(Integer, Integer))])
+    /// );
+    /// ```
+    ///
+    /// If the wildcard variable is encountered multiple times,
+    /// an invalid operator error should be returned:
+    /// ```rust
+    /// use myslip::sexp::{SExp::*, SLeaf::*, util::*};
+    /// use myslip::r#type::{Type::*, util::*, TypeError::*, PatFail::*};
+    /// assert_eq!(
+    ///     scons(var("x"), scons(var("x"), Nil)).matches_type(&List(vec![Integer, Integer])),
+    ///     Err(InvalidPattern(RepeatedVariable(
+    ///         "x".to_string(),
+    ///         scons(var("x"), scons(var("x"), Nil))
+    ///     )))
+    /// );
+    /// ```
+    ///
+    /// Then there's also rest patterns which should be appropriately typed:
+    /// ```rust
+    /// use myslip::sexp::{SExp::*, SLeaf::*, util::*};
+    /// use myslip::r#type::{Type::*, util::*, TypeError::*, PatFail::*};
+    /// assert_eq!(
+    ///     scons(var("h"), scons(RestPat("t".to_string()), Nil))
+    ///         .matches_type(&List(vec![arr(Integer, Integer), Integer, Integer, Integer])),
+    ///     Ok(vec![
+    ///         ("h".to_string(), arr(Integer, Integer)),
+    ///         ("t".to_string(), List(vec![Integer, Integer, Integer]))
+    ///     ])
+    /// );
+    /// ```
+    ///
+    /// They should also work with vectors:
+    /// ```rust
+    /// use myslip::sexp::{SExp::*, SLeaf::*, util::*};
+    /// use myslip::r#type::{Type::*, util::*, TypeError::*, PatFail::*};
+    /// assert_eq!(
+    ///     scons(var("h"), scons(RestPat("t".to_string()), Nil))
+    ///         .matches_type(&vecof(Integer)),
+    ///     Ok(vec![
+    ///         ("h".to_string(), Integer),
+    ///         ("t".to_string(), vecof(Integer))
+    ///     ])
+    /// );
+    /// ```
+    /// 
+    pub fn matches_type(&self, ty: &Type) -> Result<Vec<(String, Type)>, TypeError> {
+	todo!()
+    }
+}