How would you read input file in Scheme?

6
votes

I am trying to input data from a .txt file into a scheme structure. Each element is separated by a tab in the data file and each structure set is on a new line. I want to be able to read in the data from one line into a structure and make a list of each structure set in the file. Any suggestions?

2
scheme
What kind of structures? What scheme implementation are you using? Do you need to stick to just R5RS, or can you use impl. specific libraries, the R6RS standard library, any SRFIs? - Andrew Beyer
Does this sound like a homework assignment to anyone else? - Baxissimo

2 Answers

6
votes

Not really sure what structures you had in mind, but say you had a text file like the following:

--> cat blah.txt 
foo bar baz
1 2 3 4 5
aa bb cc dd ee

You could convert it directly into a list of lists in scheme using sed:

--> echo "(define mylist '("`sed -e 's/\(.*\)/(\1)/' blah.txt`"))" > foo.txt

which then produces the following file:

--> cat foo.txt 
(define mylist '((foo bar baz) (1 2 3 4 5) (aa bb cc dd ee)))

And now all you have to do is load the file into scheme:

(load "foo.txt")

And you can access the structure via the `mylist' variable.

3
votes

Sounds like a CSV file with tabs instead of commas. If you're using PLT Scheme (DrScheme/mzscheme) neil's csv library is probably what you want.

Here is the documentation.

Here is how to load it remotely:

(require (planet neil/csv:1:2/csv))

At least, that's what the instructions say. On my slightly oodate DrScheme, this is what worked:

(require (planet "csv.ss" ("neil" "csv.plt" 1 (= 1))))