Add support for expression syscalls

Nub.Lang/Nub.Lang/Generation/Generator.cs

@@ -146,23 +146,36 @@ public class Generator
                 GenerateFuncCall(funcCallStatement.FuncCall, func);
                 break;
             case ReturnNode @return:
-                if (@return.Value.HasValue)
-                {
-                    GenerateExpression(@return.Value.Value, func);
-                }
-                _builder.AppendLine($"    jmp {func.EndLabel}");
+                GenerateReturn(func, @return);
                 break;
             case SyscallStatementNode syscallStatement:
                 GenerateSyscall(syscallStatement.Syscall, func);
                 break;
             case VariableAssignmentNode variableAssignment:
-                throw new NotImplementedException();
+                GenerateVariableAssignment(func, variableAssignment);
                 break;
             default:
                 throw new ArgumentOutOfRangeException(nameof(statement));
         }
     }
 
+    private void GenerateReturn(Func func, ReturnNode @return)
+    {
+        if (@return.Value.HasValue)
+        {
+            GenerateExpression(@return.Value.Value, func);
+        }
+
+        _builder.AppendLine($"    jmp {func.EndLabel}");
+    }
+
+    private void GenerateVariableAssignment(Func func, VariableAssignmentNode variableAssignment)
+    {
+        GenerateExpression(variableAssignment.Value, func);
+        var variable = func.ResolveLocalVariable(variableAssignment.Name);
+        _builder.AppendLine($"    mov [rbp - {variable.Offset}], rax");
+    }
+
     private void GenerateExpression(ExpressionNode expression, Func func)
     {
         switch (expression)
@@ -180,7 +193,7 @@ public class Generator
                 GenerateStrlen(strlen, func);
                 break;
             case SyscallExpressionNode syscallExpression:
-                throw new NotImplementedException();
+                GenerateSyscall(syscallExpression.Syscall, func);
                 break;
             default:
                 throw new ArgumentOutOfRangeException(nameof(expression));

Nub.Lang/Nub.Lang/Input/program.nub

@@ -4,13 +4,9 @@ let STD_OUT = 1;
 let STD_ERR = 2;
 
 func main() {
-    write(test());
+    write("test\n");
 }
 
-func test(): String {
-    return "test";
-}
-
-func write(msg: String) {
-    syscall(SYS_WRITE, STD_OUT, msg, strlen(msg));
+func write(msg: String): int64 {
+    return syscall(SYS_WRITE, STD_OUT, msg, strlen(msg));
 }

Nub.Lang/Nub.Lang/Parsing/Parser.cs

@@ -129,6 +129,14 @@ public class Parser
 
                         return new ReturnNode(value);
                     }
+                    case Symbol.Let:
+                    {
+                        var name = ExpectIdentifier().Value;
+                        ExpectSymbol(Symbol.Assign);
+                        var value = ParseExpression();
+                        ExpectSymbol(Symbol.Semicolon);
+                        return new VariableAssignmentNode(name, value);
+                    }
                     default:
                     {
                         throw new Exception($"Unexpected symbol {symbol.Symbol}");

Nub.Lang/Nub.Lang/Typing/ExpressionTyper.cs

@@ -100,6 +100,7 @@ public class ExpressionTyper
     private void PopulateVariableAssignment(VariableAssignmentNode variableAssignment)
     {
         PopulateExpression(variableAssignment.Value);
+        _variables.Push(new Variable(variableAssignment.Name, variableAssignment.Value.Type));
     }
 
     private void PopulateExpression(ExpressionNode expression)
@@ -150,7 +151,7 @@ public class ExpressionTyper
         var type = _variables.FirstOrDefault(v => v.Name == identifier.Identifier)?.Type;
         if (type == null)
         {
-            throw new Exception($"Identifier {identifier} is not defined");
+            throw new Exception($"Variable {identifier} is not defined");
         }
         identifier.Type = type;
     }