94 lines
1.9 KiB
Elixir
94 lines
1.9 KiB
Elixir
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defmodule ExpressionEvaluator do
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def eval(expr, vars) do
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expr
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|> String.to_charlist()
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|> tokenize()
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|> run(vars)
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# |> parse()
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# |> run(vars)
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end
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@digits ?0..?9
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@alpha ?a..?z
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@operators [?+, ?-, ?*]
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def do_tokenize([first | _] = str) when first in @digits do
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{digits, rest} = Enum.split_while(str, &(&1 in @digits))
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num = digits |> to_string() |> String.to_integer()
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{{:number, num}, rest}
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end
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def do_tokenize([?( | rest]) do
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{:lparen, rest}
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end
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def do_tokenize([?) | rest]) do
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{:rparen, rest}
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end
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def do_tokenize([op | rest]) when op in @operators do
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atom = [op] |> to_string() |> String.to_atom()
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{{:operator, atom}, rest}
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end
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def do_tokenize([first | _] = str) when first in @alpha do
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{var, rest} = Enum.split_while(str, &(&1 in @alpha))
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{{:variable, var}, rest}
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end
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def tokenize([]), do: []
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def tokenize(str) do
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{token, rest} =
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str
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|> Enum.drop_while(&(&1 == ?\s))
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|> do_tokenize()
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[token | tokenize(rest)]
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end
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# def to_rpn([{:number, _} = num | rest]) do
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# [num | to_rpn(rest)]
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# end
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#
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# def to_rpn([{:operator, _} = op | rest]) do
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# [op | to_rpn(rest)]
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# end
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#
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# def to_rpn
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# def parse(tokens) do
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# {expr, rest} = do_parse(tokens)
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# [expr |
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# end
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def run([:lparen | _] = tokens, vars) do
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paren_tokens =
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tokens
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|> Enum.drop(1)
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|> Enum.reduce_while({1, []}, fn token, {count, paren_tokens} ->
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count =
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case token do
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:lparen -> count + 1
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:rparen -> count - 1
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_ -> count
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end
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if count == 0 do
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{:halt, Enum.reverse(paren_tokens)}
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else
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{:cont, {count, [token | paren_tokens]}}
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end
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end)
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# paren_expr = run(paren_tokens)
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rest_tokens = Enum.drop(tokens, length(paren_tokens))
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paren_res = run(paren_tokens, vars)
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run([{:number, paren_res} | rest_tokens])
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end
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end
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