Add logic for checking if callee is platform fn.

dmc-lib/src/asm/mod.rs

@@ -22,7 +22,7 @@ mod smoke_tests {
     fn multiple_statements() {
         let asm_functions = assemble(
             "
-            fn println() end
+            extern fn println()
             fn main()
                 let x = 42
                 println(x)

dmc-lib/src/ast/call.rs

@@ -143,14 +143,25 @@ impl Call {
                 },
             }
         }
-        let function_name = match self.callee() {
-            Expression::Identifier(identifier) => identifier.name(),
+
+        let function_symbol = match self.callee() {
+            Expression::Identifier(identifier) => {
+                let expressible_symbol = identifier.expressible_symbol();
+                match expressible_symbol {
+                    ExpressibleSymbol::Function(function_symbol) => function_symbol.clone(),
+                    _ => panic!("Calling things other than functions not yet supported."),
+                }
+            }
             _ => panic!("Calling things other than identifiers not yet supported."),
         };
 
+        if function_symbol.is_platform() {
             context.instruction(AsmInstruction::InvokePlatformStatic(
-            InvokePlatformStatic::new(function_name),
+                InvokePlatformStatic::new(function_symbol.name()),
             ));
+        } else {
+            todo!("non-platform invoke")
+        }
     }
 
     pub fn source_range(&self) -> &SourceRange {

dmc-lib/src/symbol.rs

@@ -32,6 +32,10 @@ impl FunctionSymbol {
     pub fn return_type(&self) -> TypeInfo {
         todo!()
     }
+
+    pub fn is_platform(&self) -> bool {
+        self.is_platform
+    }
 }
 
 pub struct ParameterSymbol {