[fine] Gobs of work

- Assertion improvements
- Type check function calls
- Functions in the environment
- Compile function calls

fine/tests/expression/variable.fine

@@ -1,8 +1,9 @@
 let x = 23;
 let y = x * 2;
-y;
+let z = print(y);
+z;
 
-// @type: 27 f64
+// @type: 41 f64
 // @concrete:
 // | File
 // |   LetStatement
@@ -23,15 +24,29 @@ y;
 // |       LiteralExpression
 // |         Number:'"2"'
 // |     Semicolon:'";"'
+// |   LetStatement
+// |     Let:'"let"'
+// |     Identifier:'"z"'
+// |     Equal:'"="'
+// |     CallExpression
+// |       Identifier
+// |         Identifier:'"print"'
+// |       ArgumentList
+// |         LeftParen:'"("'
+// |         Argument
+// |           Identifier
+// |             Identifier:'"y"'
+// |         RightParen:'")"'
+// |     Semicolon:'";"'
 // |   ExpressionStatement
 // |     Identifier
-// |       Identifier:'"y"'
+// |       Identifier:'"z"'
 // |     Semicolon:'";"'
 // |
 // @compiles-to:
 // | function << module >> (0 args, 0 locals):
 // |   strings (0):
-// |   code (8):
+// |   code (12):
 // |     0: PushFloat(23.0)
 // |     1: StoreModule(0)
 // |     2: LoadModule(0)
@@ -39,5 +54,9 @@ y;
 // |     4: FloatMultiply
 // |     5: StoreModule(1)
 // |     6: LoadModule(1)
-// |     7: Discard
+// |     7: LoadExternFunction(0)
+// |     8: Call(1)
+// |     9: StoreModule(2)
+// |     10: LoadModule(2)
+// |     11: Discard
 // |