add some guards for edge cases

scalar = 0 * logdist
scalar < 1 * logdist
logdist with parameters < 0
logdist with same parameters (should be scalar)
logdist with low > high

README.md

@@ -4,7 +4,7 @@ This project is a minimalist, calculator-style DSL for fermi estimation. It can
 
 ## Motivation
 
-Sometimes, [Squiggle](https://github.com/quantified-uncertainty/squiggle), [simple squiggle](https://git.nunosempere.com/quantified.uncertainty/simple-squiggle) or [squiggle.c](https://git.nunosempere.com/personal/squiggle.c) are still too complicated and un-unix-like.
+Sometimes, [Squiggle](https://github.com/quantified-uncertainty/squiggle), [simple squiggle](https://git.nunosempere.com/quantified.uncertainty/simple-squiggle) or [squiggle.c](https://git.nunosempere.com/personal/squiggle.c) are still too complicated and un-unix-like. In particular, their startup cost is not instant. 
 
 ## Installation
 
@@ -62,6 +62,7 @@ $ fermi
             beta:                          beta alpha beta
     Variable assignment:                   =: variable_name
     Variable assignment and clear stack:   =. variable_name
+    Suffixes:                              %, K, M, B, T
     Special commands:
          Comment:                          # this is a comment
          Summary stats:                    stats
@@ -94,7 +95,7 @@ Command flags:
   -echo
         Specifies whether inputs should be echoed back. Useful if reading from a file
 .  -f string
-        Specifies a file with a model to run
+        Specifies a file with a model to run. Sets the echo command to true by default.
   -n int
         Specifies the number of samples to draw when using samples (default 100000)
   -h    Shows help message
@@ -191,15 +192,20 @@ Done:
 - [x] Figure out how to make models executable, by adding a #!/bin/bash-style command at the top?
 - [x] Make -n flag work
 - [x] Add flag to repeat input lines (useful when reading from files)
+- [x] Add percentages
 
 To (possibly) do:
 
+- [ ] Fix lognormal multiplication and division by 0 or < 0
+- [ ] Consider adding an understanding of percentages
+- [ ] With the -f command line option, the program doesn't read from stdin after finishing reading the file
 - [ ] Add functions. Now easier to do with an explicit representation of the stakc
 - [ ] Think about how to draw a histogram from samples
 - [ ] Dump samples to file
 - [ ] Represent samples/statistics in some other way
 - [ ] Perhaps use qsort rather than full sorting
 - [ ] Program into a small device, like a calculator?
+- [ ] Units?
 
 Discarded: 
 

fermi.go

@@ -254,6 +254,16 @@ func multiplyBetaDists(beta1 Beta, beta2 Beta) Beta {
 	return Beta{a: beta1.a + beta2.a, b: beta1.b + beta2.b}
 }
 
+func multiplyLogDistAndScalar(l Lognormal, s Scalar) (Dist, error) {
+	if s == 0.0 {
+		return Scalar(0.0), nil
+	} else if s < 0.0 {
+		return operateDistsAsSamples(s, l, "+")
+	} else {
+		return multiplyLogDists(l, Lognormal{low: float64(s), high: float64(s)}), nil
+	}
+}
+
 func multiplyDists(old_dist Dist, new_dist Dist) (Dist, error) {
 
 	switch o := old_dist.(type) {
@@ -263,17 +273,20 @@ func multiplyDists(old_dist Dist, new_dist Dist) (Dist, error) {
 			case Lognormal:
 				return multiplyLogDists(o, n), nil
 			case Scalar:
-				return multiplyLogDists(o, Lognormal{low: float64(n), high: float64(n)}), nil
+				return multiplyLogDistAndScalar(o, n)
 			}
 		}
 	case Scalar:
 		{
-			if o == 1 {
+			switch o {
+			case 1.0:
 				return new_dist, nil
+			case 0.0:
+				return Scalar(0.0), nil
 			}
 			switch n := new_dist.(type) {
 			case Lognormal:
-				return multiplyLogDists(Lognormal{low: float64(o), high: float64(o)}, n), nil
+				return multiplyLogDistAndScalar(n, o)
 			case Scalar:
 				return Scalar(float64(o) * float64(n)), nil
 			}
@@ -304,14 +317,14 @@ func divideDists(old_dist Dist, new_dist Dist) (Dist, error) {
 					fmt.Println("Error: Can't divide by 0.0")
 					return nil, errors.New("Error: division by zero scalar")
 				}
-				return multiplyLogDists(o, Lognormal{low: 1.0 / float64(n), high: 1.0 / float64(n)}), nil
+				return multiplyLogDistAndScalar(o, Scalar(1.0/n))
 			}
 		}
 	case Scalar:
 		{
 			switch n := new_dist.(type) {
 			case Lognormal:
-				return multiplyLogDists(Lognormal{low: float64(o), high: float64(o)}, Lognormal{low: 1.0 / n.high, high: 1.0 / n.low}), nil
+				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")
@@ -374,8 +387,15 @@ func parseWordsIntoOpAndDist(words []string, vars map[string]Dist) (string, Dist
 	case 2:
 		new_low, err1 := pretty.ParseFloat(words[0])
 		new_high, err2 := pretty.ParseFloat(words[1])
-		if err1 != nil || err2 != nil {
+		switch {
+		case err1 != nil || err2 != nil:
 			return parseWordsErr("Trying to operate by a distribution, but distribution is not specified as two floats")
+		case new_low <= 0.0 || new_high <= 0.0:
+			return parseWordsErr("Trying to parse two floats as a lognormal, but the two floats must be greater than 0")
+		case new_low == new_high:
+			return parseWordsErr("Trying to parse two floats as a lognormal, but the two floats must be different. Try a single scalar instead?")
+		case new_low > new_high:
+			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:
@@ -404,7 +424,7 @@ replForLoop:
 	for {
 		new_line, _ := reader.ReadString('\n')
 		if *echo_flag {
-			fmt.Printf(new_line)
+			fmt.Print(new_line)
 		}
 		new_line_before_comments, _, _ := strings.Cut(new_line, "#")
 		new_line_trimmed := strings.TrimSpace(new_line_before_comments)
@@ -459,7 +479,7 @@ replForLoop:
 
 func main() {
 	num_samples_flag := flag.Int("n", N_SAMPLES, "Specifies the number of samples to draw when using samples")
-	filename := flag.String("f", "", "Specifies a file with a model to run")
+	filename := flag.String("f", "", "Specifies a file with a model to run. Sets the echo flag to true")
 	echo_flag := flag.Bool("echo", false, "Specifies whether inputs should be echoed back. Useful if reading from a file.")
 	help_flag := flag.Bool("h", false, "Shows help message")
 	flag.Parse()
@@ -472,6 +492,7 @@ func main() {
 	if *filename != "" {
 		file, err := os.Open(*filename)
 		if err == nil {
+			*echo_flag = true
 			reader = bufio.NewReader(file)
 		} else {
 			fmt.Printf("Error opening filename; reading from stdin instead\n")

pretty/pretty.go

@@ -72,6 +72,8 @@ func ParseFloat(word string) (float64, error) {
 	n := len(word) - 1
 	f, err := strconv.ParseFloat(word[:n], 64)
 	switch word[n] {
+	case '%':
+		return multiplyOrPassThroughError(0.01, f, err)
 	case 'K':
 		return multiplyOrPassThroughError(1_000, f, err)
 	case 'M':