1 files changed, 60 insertions, 1 deletions
diff --git a/src/type/util.rs b/src/type/util.rs
index 85e64f1..23f8d1f 100644
--- a/src/type/util.rs
+++ b/src/type/util.rs
@@ -1,5 +1,6 @@
 
-use crate::r#type::{*, Type::*};
+use crate::r#type::{*, Type::*, TypeError::*, FunDefError::*};
+use std::collections::HashMap;
 
 pub fn arr(a: impl Into<Box<Type>>, b: impl Into<Box<Type>>) -> Type {
     Arrow(a.into(), b.into())
@@ -12,3 +13,61 @@ pub fn vt(name: &str) -> Type {
 pub fn vecof(ty: impl Into<Box<Type>>) -> Type {
     VecOf(ty.into())
 }
+
+use crate::sexp::{SExp::*, SLeaf::*};
+impl SExp {
+    pub fn get_fun_type(self, mut ctx: HashMap<String, Type>) -> Result<Type, TypeError> {
+	let ls = self.clone().parts();
+	ls.get(0)
+	    .filter(|t| **t == Atom(Fun))
+	    .ok_or(InvalidFunDef(self.clone(), NoFunToken))?;
+	let argnames = ls.get(1)
+	    .ok_or(InvalidFunDef(self.clone(), NoArgumentList))?
+	    .clone().parts();
+	let argtypes = ls.get(2)
+	    .ok_or(InvalidFunDef(self.clone(), NoTypeList))?
+	    .clone();
+	let rettype  = ls.get(3)
+	    .ok_or(InvalidFunDef(self.clone(), NoReturnType))?;
+	let funbody  = ls.get(4)
+	    .ok_or(InvalidFunDef(self.clone(), NoFunctionBody))?;
+
+	let mut argnamevec = vec![];
+	for name in argnames {
+	    argnamevec.push(match name {
+		Atom(Var(s)) => Ok(s),
+		_ => Err(InvalidFunDef(self.clone(), InvalidArgumentList)),
+	    }?);
+	}
+
+	let argtypes = match argtypes.clone().multistep() {
+	    Ok(Atom(Ty(List(v)))) => Ok(v),
+	    Ok(Atom(Ty(t))) => Ok(vec![t]),
+	    _ => {
+		Err(InvalidFunDef(self.clone(), InvalidArgumentList))
+	    },
+	}?;
+
+	let rettype = match rettype.clone().multistep() {
+	    Ok(Atom(Ty(t))) => Ok(t),
+	    _ => Err(InvalidFunDef(self.clone(), InvalidReturnType))
+	}?;
+
+	let additional_ctx = argnamevec.into_iter().zip(argtypes.clone());
+	for (name, ty) in additional_ctx {
+	    ctx.insert(name, ty);
+	}
+
+	let argtype = if argtypes.len() == 0 {
+	    NilType
+	} else if argtypes.len() == 1 {
+	    argtypes[0].clone()
+	} else {
+	    List(argtypes)
+	};
+
+	funbody.infer_type(ctx)?;
+
+	Ok(arr(argtype, rettype))
+    }
+}