diff --git a/src/main.rs b/src/main.rs
index 0cac004..f5b3d3c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,8 +1,9 @@
+use std::char;
+use std::collections::HashMap;
+use std::env;
 use std::fs::File;
 use std::io;
 use std::io::Read;
-use std::env;
-use std::collections::HashMap;
 
 const EXEC_RPR: [(&'static str, i32); 28] = [
     ("entry", 1),
@@ -61,44 +62,37 @@ fn parse(contents: String, opcodes: HashMap<&'static str, (i64, i32)>) -> Vec<i6
         let tmp = line.split(" ").map(String::from).collect::<Vec<String>>();
         let (op, args) = tmp.split_first().expect("malformatted line!");
         let opcode: &str = &op.to_lowercase()[..];
-        match opcodes.get(opcode) {
-            Some(v) => {
-                code.push(v.0);
-                if args.len() as i32 != v.1 {
-                    panic!("Expected {} arguments for opcode {}, but got {}!", v.1, opcode, args.len());
-                }
-                for elem in args {
-                    match elem.parse::<i64>() {
-                        Ok(v) => code.push(v),
-                        _ => panic!("Could not parse argument {} to instruction {} as number!", elem, opcode)
-                    }
+        if let Some(v) = opcodes.get(opcode) {
+            code.push(v.0);
+            if args.len() as i32 != v.1 {
+                panic!("Expected {} arguments for opcode {}, but got {}!", v.1, opcode, args.len());
+            }
+            for elem in args {
+                if let Ok(v) = elem.parse::<i64>() {
+                    code.push(v);
                 }
             }
-            None => panic!("Do not know opcode {}!", opcode)
         }
     }
     return code
 }
 
 fn binop<F>(stack: &mut Vec<i64>, fun: F) where F: Fn(i64, i64) -> i64 {
-    let x = stack.pop();
-    let y = stack.pop();
-    match x {
-        Some(x) =>
-            match y {
-                Some(y) => stack.push(fun(x, y)),
-                _       => panic!("pop needs at least two elements on the stack")
-            },
-        _       => panic!("pop needs at least two elements on the stack")
+    if let Some(x) = stack.pop() {
+        if let Some(y) = stack.pop() {
+            stack.push(fun(x, y));
+            return;
+        }
     }
+    panic!("pop needs at least two elements on the stack");
 }
 
 fn exec(instructions: Vec<i64>) -> i64 {
     let mut stack: Vec<i64> = Vec::new();
+    let mut data: Vec<i64> = Vec::new();
     let ilen = instructions.len();
     let mut ip = 0;
     while ip < ilen {
-        ip += 1; /* TMP */
         match instructions[ip] {
             /* ENT */ 0 => (),
             /* ADD */ 1 => binop(&mut stack, |x, y| x + y),
@@ -112,24 +106,49 @@ fn exec(instructions: Vec<i64>) -> i64 {
             /* BR  */ 9 => (),
             /* BRT */ 10 => (),
             /* BRF */ 11 => (),
-            /* CST */ 12 => (),
+            /* CST */ 12 => {
+                ip += 1;
+                stack.push(instructions[ip])
+            },
             /* LD  */ 13 => (),
             /* GLD */ 14 => (),
             /* ST  */ 15 => (),
             /* GST */ 16 => (),
-            /* PRN */ 17 => (),
-            /* POP */ 18 => (),
+            /* PRN */ 17 => {
+                if let Some(x) = stack.last() {
+                    if let Some(x) = char::from_digit(*x as u32, 10) {
+                        print!("{}", x);
+                    }
+                }
+            },
+            /* POP */ 18 => {
+                stack.pop();
+                ();
+            }
             /* HLT */ 19 => break,
             /* LEQ */ 20 => binop(&mut stack, |x, y| (x <= y) as i64),
             /* GEQ */ 21 => binop(&mut stack, |x, y| (x >= y) as i64),
             /* CAL */ 22 => (),
             /* RET */ 23 => (),
-            /* IPR */ 24 => (),
+            /* IPR */ 24 => {
+                if let Some(x) = stack.last() {
+                    print!("{}", x);
+                };
+            },
             /* FET */ 25 => (),
-            /* INC */ 26 => (),
-            /* DEC */ 27 => (),
+            /* INC */ 26 => {
+                if let Some(x) = stack.pop() {
+                    stack.push(x+1);
+                }
+            },
+            /* DEC */ 27 => {
+                if let Some(x) = stack.pop() {
+                    stack.push(x-1);
+                }
+            },
             /* IMP */ x => panic!("Unknown instruction {}!", x)
         }
+        ip += 1;
     }
     return *stack.first().unwrap_or(&0);
 }