setup main to specify an entry point

src/main.rs

@@ -3,26 +3,49 @@ mod ast;
 
 lalrpop_mod!(pub grammar); // synthesized by LALRPOP
 
+use std::fs;
+use std::io::Write;
 mod compiler;
 use inkwell::context::Context;
+extern crate clap;
+use clap::{Arg, App};
+
 
 fn main() {
-    let module_ast = grammar::ModuleParser::new().parse("
-    fn add(a, b) {
-        a + b
-    }
-    fn subtract(a, b) {
-        a - b
-    }
-    fn main() {
-        add(4, subtract(5, 2))
-    }
-    ").unwrap();
+    let matches = App::new("Boring Language Compiler")
+                          .version("0.0.1")
+                          .author("Andrew Segavac")
+                          .about("Compiles boring language files to LLVM IR.")
+                          .arg(Arg::with_name("OUTPUT")
+                               .short("o")
+                               .long("out")
+                               .value_name("OUTOUT")
+                               .help("Sets an output file")
+                               .takes_value(true))
+                          .arg(Arg::with_name("INPUT")
+                               .help("Sets the input file")
+                               .required(true)
+                               .index(1))
+                          .arg(Arg::with_name("v")
+                               .short("v")
+                               .multiple(true)
+                               .help("Sets the level of verbosity"))
+                          .get_matches();
+    let input = matches.value_of("INPUT").unwrap();
+
+    let default_output = input.rsplitn(2, ".").collect::<Vec<&str>>().last().unwrap().clone();
+    let output = matches.value_of("OUTPUT").unwrap_or(default_output);
+
+    let contents = fs::read_to_string(input).expect("input file not found");
+    let module_ast =  grammar::ModuleParser::new().parse(&contents).unwrap(); //TODO: convert to error
+
 
     let context = Context::create();
     let mut code_gen = compiler::ModuleCodeGen::new(&context, "main".to_string());
     code_gen.gen_module(module_ast);
-    println!("{}", code_gen.dump());
+
+    let mut f = fs::File::create(output).expect("Unable to create out file");
+    f.write_all(code_gen.dump().as_bytes()).expect("Unable to write data");
 }