The REPL
The REPL allows you to input Urn code and execute it immediately. This is immensely useful, as it allows you to quickly
test something, be it a built-in function or a new idea you had. You can launch the REPL by running Urn with no
arguments, or using the --repl flag.
For ease-of-use and efficiency, the REPL differs slightly from normal compilation:
- No optimisation passes or static analysis is performed.
- You can override top-level definitions in subsequent inputs. Note that expressions that referenced the original definition will not be changed.
The REPL also comes with several “commands”, which can be used to query various aspects of the running state. These can
be seen using the :help (or :h) command:
:[d]oc NAME
This command allows you to fetch the doc-string of a symbol in the current scope.
> :doc car
(list/car x)
Return the first element present in the list X. This function operates
in constant time.
### Example:
> (car '(1 2 3))
out = 1
:module NAME
This will search for loaded modules with the given name, displaying the defined symbols and the module-level doc-string. Note that this will not attempt to load the module if it cannot be found: you will have to import it normally first.
> :module table
table
Located at lib/table
Exported symbols
.<! .> assoc assoc->struct assoc? copy-of create-lookup empty-struct? extend fast-struct ...
:[r]eload
This finds modules which have changed on disk, and reloads them along with any files which depend on them. This allows you to quickly edit + refresh code without having to continuously restart the REPL.
:[s]earch QUERY
The search command will look for symbols and doc-strings matching the given pattern. You can use :doc to get further
information about a given command.
> :search car
Search by function name:
cars car
Search by function docs:
destructuring-bind head map maybe-map loop car
:[v]iew NAME
Pretty print the source code of the given symbol’s definition.
> :view car
(defun car (x)
"Return the first element present in the list X. This function operates
in constant time."
(assert-type! x list)
(base/car x))