Add a command line parsing procedure

source/Compiler.elna

@@ -1,18 +1,51 @@
 module Compiler;
 
-from FIO import StdIn;
+from FIO import Close, IsNoError, File, OpenToRead, StdErr, StdOut, WriteLine, WriteString;
 from SYSTEM import ADR;
+from M2RTS import HALT, ExitOnHalt;
 
 from Lexer import Lexer, lexer_destroy, lexer_initialize;
 from Transpiler import transpile;
+from CommandLineInterface import PCommandLine, parse_command_line;
 
+var
+  command_line: PCommandLine;
+
+proc compile_from_stream();
 var
   lexer: Lexer;
+  source_input: File;
+begin
+  source_input := OpenToRead(command_line^.input);
+
+  if IsNoError(source_input) = false then
+    WriteString(StdErr, 'Fatal error: failed to read the input file "');
+    WriteString(StdErr, command_line^.input);
+    WriteString(StdErr, '".');
+    WriteLine(StdErr);
+
+    ExitOnHalt(2)
+  end;
+  if IsNoError(source_input) then
+    lexer_initialize(ADR(lexer), source_input);
+
+    transpile(ADR(lexer), StdOut);
+
+    lexer_destroy(ADR(lexer));
+
+    Close(source_input)
+  end
+end;
 
 begin
-  lexer_initialize(ADR(lexer), StdIn);
+  ExitOnHalt(0);
+  command_line := parse_command_line();
 
-  transpile(ADR(lexer));
-
-  lexer_destroy(ADR(lexer))
+  if command_line <> nil then
+    compile_from_stream()
+  end;
+  if command_line = nil then
+    ExitOnHalt(1)
+  end;
+  HALT()
 end Compiler.