diff --git a/fermi b/fermi
index bc9a06f..4d4c44f 100755
Binary files a/fermi and b/fermi differ
diff --git a/main/error.go b/main/error.go
new file mode 100644
index 0000000..31487d5
--- /dev/null
+++ b/main/error.go
@@ -0,0 +1,23 @@
+package main
+
+import (
+	"fmt"
+)
+
+type FermiError struct {
+	Code string
+	Msg  string
+}
+
+func (e FermiError) Error() string {
+	return e.Msg
+}
+
+func PrintError(e error) {
+	if fermi_error, ok := e.(FermiError); ok {
+		fmt.Printf("Error: %s: %s\n", fermi_error.Code, fermi_error.Msg)
+		fmt.Printf("Type \"help\" or \"h\" to see grammar and command flags\n")
+	} else {
+		fmt.Printf("Error: %s\n", e.Error())
+	}
+}
diff --git a/main/errors.go b/main/errors.go
deleted file mode 100644
index 834cc21..0000000
--- a/main/errors.go
+++ /dev/null
@@ -1,10 +0,0 @@
-package main
-
-type MyError struct {
-	Code string
-	Msg  string
-}
-
-func (me MyError) Error() string {
-	return me.Msg
-}
diff --git a/main/fermi.go b/main/fermi.go
index 6e67f3b..10acba7 100644
--- a/main/fermi.go
+++ b/main/fermi.go
@@ -2,7 +2,6 @@ package main
 
 import (
 	"bufio"
-	"errors"
 	"flag"
 	"fmt"
 	"git.nunosempere.com/NunoSempere/fermi/sample"
@@ -84,7 +83,7 @@ const HELP_MSG = "1. Grammar:\n" +
 	"    + 1 10\n" +
 	"    * beta 1 10\n" +
 	"    1 10 (multiplication taken as default operation)\n" +
-	"      =: x\n" +
+	"    =: x\n" +
 	"    .\n" +
 	"    1 100\n" +
 	"    + x\n" +
@@ -94,6 +93,9 @@ const HELP_MSG = "1. Grammar:\n" +
 	"    1 10\n" +
 	"    + beta 1 100\n" +
 	"    )\n" +
+	"    =. y\n" +
+	"    mx x 1 y 2.33\n" +
+	"    + mx x 30% y 70%\n" +
 	"    exit\n" +
 	"\n" +
 	"2. Command flags:\n" +
@@ -103,7 +105,7 @@ const HELP_MSG = "1. Grammar:\n" +
 	"        Specifies a file with a model to run\n" +
 	"  -n int\n" +
 	"        Specifies the number of samples to draw when using samples (default 100000)\n" +
-	"  -h    Shows help message\n"
+	"  -h    Shows help message"
 
 const NORMAL90CONFIDENCE = 1.6448536269514727
 const INIT_DIST Scalar = Scalar(1)
@@ -126,16 +128,16 @@ func operateDistsAsSamples(dist1 Dist, dist2 Dist, op string) (Dist, error) {
 			if ys[0] != 0 {
 				zs[i] = xs[i] / ys[i]
 			} else {
-				fmt.Println("Error: When dividing as samples, division by zero")
-				return nil, errors.New("Division by zero")
+				// fmt.Println("Error: When dividing as samples, division by zero")
+				return nil, FermiError{Code: "Division by zero", Msg: "When operating on samples, division by zero"}
 			}
 		case "+":
 			zs[i] = xs[i] + ys[i]
 		case "-":
 			zs[i] = xs[i] - ys[i]
 		default:
-			fmt.Println("Error: Operation not recognized")
-			return nil, errors.New("Operation not recognized")
+			// fmt.Println("Error: Operation not recognized")
+			return nil, FermiError{Code: "Unknown operation", Msg: "When operating on samples, operation not recognized"}
 		}
 	}
 
@@ -210,14 +212,12 @@ func divideDists(old_dist Dist, new_dist Dist) (Dist, error) {
 			switch n := new_dist.(type) {
 			case Lognormal:
 				if n.high == 0 || n.low == 0 {
-					fmt.Println("Error: Can't divide by 0.0")
-					return nil, errors.New("Error: division by zero")
+					return nil, FermiError{Code: "Division by zero", Msg: "When operating two lognormals, one of the parameters is zero, which would result in division by zero"}
 				}
 				return multiplyLogDists(o, Lognormal{low: 1.0 / n.high, high: 1.0 / n.low}), nil
 			case Scalar:
 				if n == 0.0 {
-					fmt.Println("Error: Can't divide by 0.0")
-					return nil, errors.New("Error: division by zero scalar")
+					return nil, FermiError{Code: "Division by zero", Msg: "When operating a lognormal with a scalar, trying to divide but the scalar is zero"}
 				}
 				return multiplyLogDistAndScalar(o, Scalar(1.0/n))
 			}
@@ -229,8 +229,7 @@ func divideDists(old_dist Dist, new_dist Dist) (Dist, error) {
 				return multiplyLogDistAndScalar(Lognormal{low: 1.0 / n.high, high: 1.0 / n.low}, o)
 			case Scalar:
 				if n == 0.0 {
-					fmt.Println("Error: Can't divide by 0.0")
-					return nil, errors.New("Error: division by zero scalar")
+					return nil, FermiError{Code: "Division by zero", Msg: "When operating two scalars, trying to divide but the divisor is is zero"}
 				}
 				return Scalar(float64(o) / float64(n)), nil
 			}
@@ -251,7 +250,7 @@ func operateDists(old_dist Dist, new_dist Dist, op string) (Dist, error) {
 	case "-":
 		return operateDistsAsSamples(old_dist, new_dist, "-")
 	default:
-		return nil, PrintAndReturnErr("Can't combine distributions in this way")
+		return nil, FermiError{Code: "Unknown operation", Msg: "When operating distributions, operation not recognized"}
 	}
 }
 
@@ -259,9 +258,17 @@ func operateDists(old_dist Dist, new_dist Dist, op string) (Dist, error) {
 func parseMixture(words []string, vars map[string]Dist) (Dist, error) {
 	// mx, mix, var weight var weight var weight ...
 	// Check syntax
-	if len(words)%2 != 0 {
-		return nil, PrintAndReturnErr("Not a mixture. \nMixture syntax: \nmx x 2.5 y 8 z 10\ni.e.: mx var weight var2 weight2 ... var_n weight_n")
+	switch {
+	case len(words) < 1:
+		return nil, FermiError{Code: "Not a mixture", Msg: "Input can't be a mixture, since it doesn't have enough words"}
+	case words[0] != "mx":
+		return nil, FermiError{Code: "Not a mixture", Msg: "Input can't be a mixture, since it is not preceded by the mx keyword"}
+	case len(words)%2 != 1:
+		return nil, FermiError{Code: "Not a mixture", Msg: "When parsing a mixture, input doesn't have equal number of variables and weights. \nMixture syntax: \nmx x 20% y 70% z 10%\ni.e.: mx var weight var2 weight2 ... var_n weight_n"}
+	case len(words) < 5:
+		return nil, FermiError{Code: "Not a mixture", Msg: "When parsing a mixture, not enough words. \nMixture syntax: \nmx x 20% y 70% z 10%\ni.e.: mx var weight var2 weight2 ... var_n weight_n"}
 	}
+	words = words[1:] // crop "mx" at the beginning
 
 	var fs []func(int, sample.State) float64
 	var weights []float64
@@ -270,14 +277,14 @@ func parseMixture(words []string, vars map[string]Dist) (Dist, error) {
 		if i%2 == 0 {
 			dist, exists := vars[word]
 			if !exists {
-				return nil, PrintAndReturnErr("Expected mixture variable but didn't get a variable. \nMixture syntax: \nmx x 2.5 y 8 z 10\ni.e.: mx var weight var2 weight2 ... var_n weight_n")
+				return nil, FermiError{Code: "Not a mixture variable", Msg: "When parsing a mixture, expected mixture variable but didn't get a variable. \nMixture syntax: \nmx x 2.5 y 8 z 10\ni.e.: mx var weight var2 weight2 ... var_n weight_n"}
 			}
 			f := dist.Sampler
 			fs = append(fs, f)
 		} else {
 			weight, err := ParseFloat(word)
 			if err != nil {
-				return nil, PrintAndReturnErr("Expected mixture weight but didn't get a float. \nMixture syntax: \nmx x 2.5 y 8 z 10\ni.e.: mx var weight var2 weight2 ... var_n weight_n")
+				return nil, FermiError{Code: "Not a mixture weight", Msg: "When parsing a mixture, expected mixture weight but didn't get a variable. \nMixture syntax: \nmx x 2.5 y 8 z 10\ni.e.: mx var weight var2 weight2 ... var_n weight_n"}
 			}
 			weights = append(weights, weight)
 		}
@@ -291,26 +298,26 @@ func parseMixture(words []string, vars map[string]Dist) (Dist, error) {
 }
 
 /* Parser and repl */
-func parseWordsErr(err_msg string) (string, Dist, error) {
-	return "", nil, PrintAndReturnErr(err_msg)
-}
 func parseWordsIntoOpAndDist(words []string, vars map[string]Dist) (string, Dist, error) {
+	parseWordsErr := func(msg string) (string, Dist, error) {
+		return "", nil, FermiError{Code: "Malformed input", Msg: "When parsing words into operator and distribution: " + msg}
+	}
 
 	op := ""
 	var dist Dist
 
 	switch words[0] {
-	case "*", "/", "+", "-", "mx":
+	case "*", "/", "+", "-":
 		op = words[0]
 		words = words[1:]
 	default:
 		op = "*"
 	}
 
-	switch len(words) {
-	case 0:
+	switch {
+	case len(words) == 0:
 		return parseWordsErr("Operator must have operand; can't operate on nothing")
-	case 1:
+	case len(words) == 1:
 		var_word, var_word_exists := vars[words[0]]
 		single_float, err1 := ParseFloat(words[0]) // abstract this away to search for K/M/B/T/etc.
 		switch {
@@ -321,7 +328,7 @@ func parseWordsIntoOpAndDist(words []string, vars map[string]Dist) (string, Dist
 		case err1 != nil && !var_word_exists:
 			return parseWordsErr("Trying to operate on a scalar, but scalar is neither a float nor an assigned variable")
 		}
-	case 2:
+	case len(words) == 2:
 		new_low, err1 := ParseFloat(words[0])
 		new_high, err2 := ParseFloat(words[1])
 		switch {
@@ -335,7 +342,7 @@ func parseWordsIntoOpAndDist(words []string, vars map[string]Dist) (string, Dist
 			return parseWordsErr("Trying to parse two floats as a lognormal, but the first number is larger than the second number")
 		}
 		dist = Lognormal{low: new_low, high: new_high}
-	case 3:
+	case len(words) == 3:
 		switch {
 		case words[0] == "beta" || words[0] == "b":
 			a, err1 := ParseFloat(words[1])
@@ -347,18 +354,12 @@ func parseWordsIntoOpAndDist(words []string, vars map[string]Dist) (string, Dist
 		default:
 			return parseWordsErr("Input not understood or not implemented yet")
 		}
-	default:
-		switch op {
-		case "mx":
-			tmp, err := parseMixture(words, vars)
-			if err != nil {
-				return parseWordsErr("Error parsing a mixture: " + err.Error())
-			}
-			dist = tmp
-			op = "*"
-		default:
-			return parseWordsErr("Input not understood or not implemented yet")
+	case len(words) >= 4: // four or more words
+		if words[0] == "mx" {
+			dist, err := parseMixture(words, vars)
+			return op, dist, err
 		}
+		return parseWordsErr("Input not understood or not implemented yet")
 	}
 	return op, dist, nil
 }
@@ -379,17 +380,11 @@ replForLoop:
 		words := strings.Split(new_line_trimmed, " ")
 
 		switch {
-		case strings.TrimSpace(new_line_trimmed) == "": /* Empty line case */
+
+		/* Empty line */
+		case strings.TrimSpace(new_line_trimmed) == "":
 			continue replForLoop
-		/* Parenthesis */
-		case len(words) == 2 && (words[0] == "*" || words[0] == "+" || words[0] == "-" || words[0] == "/") && words[1] == "(":
-			new_stack := runRepl(Stack{old_dist: INIT_DIST, vars: stack.vars}, reader, echo_flag)
-			combined_dist, err := operateDists(stack.old_dist, new_stack.old_dist, words[0])
-			if err == nil {
-				stack.old_dist = combined_dist
-			}
-		case len(words) == 1 && words[0] == ")":
-			return stack
+
 		/* Special operations */
 		case words[0] == "exit" || words[0] == "e":
 			os.Exit(0)
@@ -402,6 +397,7 @@ replForLoop:
 			fmt.Println()
 		case words[0] == "stats" || words[0] == "s":
 			PrettyPrintStats(stack.old_dist)
+
 		/* Variable assignment */
 		case words[0] == "=:" && len(words) == 2:
 			stack.vars[words[1]] = stack.old_dist
@@ -411,16 +407,36 @@ replForLoop:
 			fmt.Printf("%s ", words[1])
 			PrettyPrintDist(stack.old_dist)
 			stack.old_dist = INIT_DIST
+
+		/* Parenthesis */
+		case len(words) == 2 && (words[0] == "*" || words[0] == "+" || words[0] == "-" || words[0] == "/") && words[1] == "(":
+			new_stack := runRepl(Stack{old_dist: INIT_DIST, vars: stack.vars}, reader, echo_flag)
+			combined_dist, err := operateDists(stack.old_dist, new_stack.old_dist, words[0])
+			if err != nil {
+				PrintError(err)
+			} else {
+				stack.old_dist = combined_dist
+			}
+		case len(words) == 1 && words[0] == ")":
+			return stack
+
+		/* Bread and butter distribution operations */
 		default:
 			op, new_dist, err := parseWordsIntoOpAndDist(words, stack.vars)
 			if err != nil {
+				PrintError(err)
+				PrettyPrintDist(stack.old_dist)
 				continue replForLoop
 			}
 			combined_dist, err := operateDists(stack.old_dist, new_dist, op)
-			if err == nil {
-				stack.old_dist = combined_dist
+			if err != nil {
+				PrintError(err)
+				PrettyPrintDist(stack.old_dist)
+				continue replForLoop
 			}
+			stack.old_dist = combined_dist
 		}
+
 		PrettyPrintDist(stack.old_dist)
 	}
 }
diff --git a/makefile b/makefile
index b138a13..0e4ab0e 100644
--- a/makefile
+++ b/makefile
@@ -1,5 +1,5 @@
 build:
-	go build main/fermi.go main/pretty.go
+	go build main/fermi.go main/pretty.go main/error.go
 
 run:
 	go run fermi.go