Arithmetic evaluation: Difference between revisions
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21/4</pre> |
21/4</pre> |
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=={{header|Clojure}}== |
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<lang Clojure>(def precedence '{* 0, / 0 |
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+ 1, - 1}) |
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(defn order-ops |
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"((A x B) y C) or (A x (B y C)) depending on precedence of x and y" |
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[[A x B y C & more]] |
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(let [ret (if (<= (precedence x) |
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(precedence y)) |
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(list (list A x B) y C) |
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(list A x (list B y C)))] |
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(if more |
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(recur (concat ret more)) |
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ret))) |
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(defn add-parens |
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"Tree walk to add parens. All lists are length 3 afterwards." |
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[s] |
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(clojure.walk/postwalk |
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#(if (seq? %) |
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(let [c (count %)] |
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(cond (even? c) (throw (Exception. "Must be an odd number of forms")) |
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(= c 1) (first %) |
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(= c 3) % |
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(>= c 5) (order-ops %))) |
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%) |
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s)) |
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(defn make-ast |
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"Parse a string into a list of numbers, ops, and lists" |
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[s] |
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(-> (format "'(%s)" s) |
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(.replaceAll , "([*+-/])" " $1 ") |
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load-string |
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add-parens)) |
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(def ops {'* * |
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'+ + |
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'- - |
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'/ /}) |
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(def eval-ast |
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(partial clojure.walk/postwalk |
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#(if (seq? %) |
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(let [[a o b] %] |
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((ops o) a b)) |
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%))) |
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(defn evaluate [s] |
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"Parse and evaluate an infix arithmetic expression" |
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(eval-ast (make-ast s))) |
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user> (evaluate "1 + 2*(3 - 2*(3 - 2)*((2 - 4)*5 - 22/(7 + 2*(3 - 1)) - 1)) + 1") |
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60</lang> |
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=={{header|D}}== |
=={{header|D}}== |