Implement primitive procedure application

src/interpreter.rs

@@ -1,15 +1,15 @@
 use crate::parser::Datum;
 use crate::parser::Datum::*;
-
-fn add(args: Vec<Datum>) -> Datum {
-    Number(42)
-}
+use crate::primitives::*;
+use std::mem;
 
 fn lookup_variable_value(exp: Datum) -> Datum {
     if let Symbol(string) = exp {
         match string.as_str() {
             "+" => Procedure(add),
-            _ => panic!("unbound-variable {:?}", string)
+            "*" => Procedure(mul),
+            "-" => Procedure(sub),
+            _ => panic!("unbound-variable {:?}", string),
         }
     } else {
         panic!("LOOKUP-VARIABLE-VALUE -- not-a-symbol {:?}", exp)
@@ -18,9 +18,19 @@ fn lookup_variable_value(exp: Datum) -> Datum {
 
 fn application(exp: Datum) -> Datum {
     if let List(vector) = exp {
-        vector[0]
+        if vector.len() == 0 {
+            panic!("Application needs at least a procedure")
+        }
+
+        let mut args: Vec<Datum> = vector.into_iter().map(interpret).collect();
+        if let Procedure(proc) = mem::take(&mut args[0]) {
+            // FIXME: call procedures with args only
+            proc(args)
+        } else {
+            panic!("The object {:?} is not applicable", args[0])
+        }
     } else {
-        panic!("APPLICATION -- cannot-apply {:?}", exp)
+        panic!("Cannot apply {:?}", exp)
     }
 }
 
@@ -29,6 +39,6 @@ pub fn interpret(exp: Datum) -> Datum {
         Boolean(_) | Number(_) => exp,
         Symbol(_) => lookup_variable_value(exp),
         List(_) => application(exp),
-        _ => panic!("unknown-expression {:?}", exp)
+        _ => panic!("unknown-expression {:?}", exp),
     }
-}
+}