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;; Nix as a Lisp
(require 'cl-lib)
(require 'json)
(require 's)
(require 'dash)
(defun nisp/expr (form)
"Entrypoint for Nisp->Nix transformation. Will translate FORM
into Nix code, if it is a valid Nisp expression.
To make code generation slightly easier, each
expression (including literals) is wrapped in an extra pair of
parens."
(concat
"("
(pcase form
;; Special keywords
('() "null")
(`(let . ,rest) (nisp/let form))
(`(fn . ,rest) (nisp/fn form))
(`(if ,cond ,then ,else) (nisp/if cond then else))
;; Nix operators & builtins that need special handling
(`(or ,lhs ,rhs) (nisp/infix "||" lhs rhs))
(`(and ,lhs ,rhs) (nisp/infix "&&" lhs rhs))
(`(> ,lhs ,rhs) (nisp/infix ">" lhs rhs))
(`(< ,lhs ,rhs) (nisp/infix "<" lhs rhs))
(`(>= ,lhs ,rhs) (nisp/infix ">=" lhs rhs))
(`(<= ,lhs ,rhs) (nisp/infix "<=" lhs rhs))
(`(+ ,lhs ,rhs) (nisp/infix "+" lhs rhs))
(`(- ,lhs ,rhs) (nisp/infix "-" lhs rhs))
(`(* ,lhs ,rhs) (nisp/infix "*" lhs rhs))
(`(/ ,lhs ,rhs) (nisp/infix "/" lhs rhs))
(`(-> ,lhs ,rhs) (nisp/infix "->" lhs rhs))
(`(? ,lhs ,rhs) (nisp/infix "?" lhs rhs))
(`(// ,lhs ,rhs) (nisp/infix "//" lhs rhs))
(`(++ ,lhs ,rhs) (nisp/infix "++" lhs rhs))
(`(== ,lhs ,rhs) (nisp/infix "==" lhs rhs))
(`(!= ,lhs ,rhs) (nisp/infix "!=" lhs rhs))
(`(! ,term) (concat "!" (nisp/expr term)))
(`(- ,term) (concat "-" (nisp/expr term)))
;; Attribute sets
(`(attrs . ,rest) (nisp/attribute-set form))
;; Function calls
((and `(,func . ,args)
(guard (symbolp func)))
(nisp/funcall func args))
;; Primitives
((pred stringp) (json-encode-string form))
((pred numberp) (json-encode-number form))
((pred keywordp) (substring (symbol-name form) 1))
((pred symbolp) (symbol-name form))
;; Lists
((pred arrayp) (nisp/list form))
(other (error "Encountered unhandled form: %s" other)))
")"))
(defun nisp/infix (op lhs rhs)
(concat (nisp/expr lhs) " " op " " (nisp/expr rhs)))
(defun nisp/funcall (func args)
(concat (symbol-name func) " " (s-join " " (-map #'nisp/expr args))))
(defun nisp/let (form)
(pcase form
(`(let . (,bindings . (,body . ()))) (concat "let "
(nisp/let bindings)
(nisp/expr body)))
(`((:inherit . ,inherits) . ,rest) (concat (nisp/inherit (car form))
" "
(nisp/let rest)))
(`((,name . (,value . ())) .,rest) (concat (symbol-name name) " = "
(nisp/expr value) "; "
(nisp/let rest)))
('() "in ")
(other (error "malformed form '%s' in let expression" other))))
(defun nisp/inherit (form)
(pcase form
(`(:inherit . ,rest) (concat "inherit " (nisp/inherit rest)))
(`((,source) . ,rest) (concat "(" (symbol-name source) ") " (nisp/inherit rest)))
(`(,item . ,rest) (concat (symbol-name item) " " (nisp/inherit rest)))
('() ";")))
(defun nisp/if (cond then else)
(concat "if " (nisp/expr cond)
" then " (nisp/expr then)
" else " (nisp/expr else)))
(defun nisp/list (form)
(cl-check-type form array)
(concat "[ "
(mapconcat #'nisp/expr form " ")
"]"))
(defun nisp/attribute-set (form)
"Attribute sets have spooky special handling because they are
not supported by the reader."
(pcase form
(`(attrs . ,rest) (concat "{ " (nisp/attribute-set rest)))
((and `(,name . (,value . ,rest))
(guard (keywordp name)))
(concat (substring (symbol-name name) 1) " = "
(nisp/expr value) "; "
(nisp/attribute-set rest)))
('() "}")))
(defun nisp/fn (form)
(pcase form
(`(fn ,args ,body) (concat
(cl-loop for arg in args
concat (format "%s: " arg))
(nisp/expr body)))))
;; The following functions are not part of the transform.
(defun nisp/eval (form)
(interactive "sExpression: ")
(when (stringp form)
(setq form (read form)))
(message
;; TODO(tazjin): Construct argv manually to avoid quoting issues.
(s-chomp
(shell-command-to-string
(concat "nix-instantiate --eval -E '" (nisp/expr form) "'")))))
(defun nisp/eval-last-sexp ()
(interactive)
(nisp/eval (edebug-last-sexp)))
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