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Allow instructions to indicate they should be ignored

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`make-instruction` will ignore any instructions that return `:ignore-instruction`. This allows instructions to be skipped without consuming their arguments.
This commit is contained in:
Erik Rauer 2020-12-11 14:00:06 -06:00 committed by Nic McPhee
parent fc26886815
commit b3d9d89f4c
1 changed files with 8 additions and 2 deletions
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10
src/propeller/push/utils/helpers.cljc
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@ -28,7 +28,11 @@
;; A utility function for making Push instructions. Takes a state, a function ;; A utility function for making Push instructions. Takes a state, a function
;; to apply to the args, the stacks to take the args from, and the stack to ;; to apply to the args, the stacks to take the args from, and the stack to
;; return the result to. Applies the function to the args (popped from the ;; return the result to. Applies the function to the args (popped from the
;; given stacks), and pushes the result onto the return-stack ;; given stacks), and pushes the result onto the return-stack.
;;
;; If the function returns :ignore-instruction, then we will return the
;; initial state unchanged. This allows instructions to fail gracefully
;; without consuming stack values.
(defn make-instruction (defn make-instruction
[state function arg-stacks return-stack] [state function arg-stacks return-stack]
(let [popped-args (get-args-from-stacks state arg-stacks)] (let [popped-args (get-args-from-stacks state arg-stacks)]
@ -36,7 +40,9 @@
state state
(let [result (apply function (:args popped-args)) (let [result (apply function (:args popped-args))
new-state (:state popped-args)] new-state (:state popped-args)]
(state/push-to-stack new-state return-stack result))))) (if (= result :ignore-instruction)
state
(state/push-to-stack new-state return-stack result))))))
;; Given a set of stacks, returns all instructions that operate on those stacks ;; Given a set of stacks, returns all instructions that operate on those stacks
;; only. Won't include random instructions unless :random is in the set as well ;; only. Won't include random instructions unless :random is in the set as well