sets echo on by default with read from file flag

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
 
@@ -94,7 +94,7 @@ 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
@@ -194,6 +194,7 @@ Done:
 
 To (possibly) do:
 
+- [ ] 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

fermi.go

@@ -459,7 +459,7 @@ 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 +472,7 @@ 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")