This patch adds a setting, Control.carryDeclaration, which stores the name of an sml file with a single variable (val, val rec, or fun) declaration. When code is loaded in to the repl, if it contains any variables with the same name, the last declaration of such a variable will be replaced with the code in carryDeclaration.
Given two files,
map.sml
fun map f [] = []
| map f (x::xs) = (f x) :: (map f xs)
student-code.sml
fun map f L = []
fun incr L = map (fn x => x + 1) L
val L = incr [1, 2]
The student's incr function will be incorrect because their map function is incorrect, not because their incr function is implemented wrong. We want to fix this by substituting the correct map.sml code for the student's map declaration.
Standard ML of New Jersey v110.82 [built: Wed Dec 13 23:38:01 2017]
- Control.carryDeclaration := "map.sml";
val it = () : unit
- use "student-code.sml"
[opening student-code.sml]
There was 1 occurrance of map
One was replaced.
val map = fn : ('a -> 'b) -> 'a list -> 'b list
val incr = fn : int list -> int list
val L = [2,3] : int list
val it = () : unit
-
Different types of declarations can be freely interchanged - fun, val, and val rec are all treated the same way.
This does not yet support code with structures, though I plan to add that at some point.
This patch uses Jacob Van Buren's install script from https://github.com/jvanburen/smlnj-warn-unused, with minor modifications. You should also check out his unused variable warning patch!
These instructions are also taken from his page and modified. (Thanks Jacob!)
bash -c "$(curl -fsSL https://raw.githubusercontent.com/jluningp/smlnj-carry-error/master/install.sh)"bash -c "$(wget https://raw.githubusercontent.com/jluningp/smlnj-carry-error/master/install.sh -O -)"Move the created directory into the appropriate location on your computer (/usr/local/smlnj/ on macOS at least). Either add the bin folder to your PATH variable, or add a symlink to it the smlnj-110.82/bin/sml executable in /usr/local/bin.