Evaluation: : slurp and unslurp

LFE provides a unique and powerful way to evaluate file contents directly in the REPL through the slurp and unslurp commands. This feature allows you to temporarily import function and macro definitions from files into your current REPL session.

Using slurp

The slurp function reads an LFE source file and makes all functions and macros defined in that file available directly in the shell, without requiring module prefixes:

lfe> (slurp "examples/my-functions.lfe")
#(ok -no-mod-)
lfe> $ENV
;; Shows all the new function and macro definitions from the file

Key characteristics of slurp:

• Only one file can be slurped at a time
• Slurping a new file automatically removes all data from the previously slurped file
• Functions and macros become available without module prefixes
• The code is evaluated in the current REPL environment
• Variable bindings from the file are added to your current session

Using unslurp

The unslurp command reverts the REPL back to the state before the last slurp, removing all function and macro definitions that were imported:

lfe> (unslurp)
ok
lfe> $ENV
;; Back to the original environment state

This is particularly useful when experimenting with different versions of functions or when you want to clean up your REPL environment.

Practical Example

Let's say you have a file called math-utils.lfe:

(defun double (x)
  (* x 2))

(defun square (x)
  (* x x))

(defmacro when-positive (x body)
  `(if (> ,x 0) ,body 'not-positive))

After slurping this file:

lfe> (slurp "math-utils.lfe")
#(ok -no-mod-)
lfe> (double 21)
42
lfe> (square 6)
36
lfe> (when-positive 5 'yes)
yes
lfe> (when-positive -1 'yes)
not-positive