39 lines
804 B
Gleam
39 lines
804 B
Gleam
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import gleam/option.{type Option, None, Some}
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/// Stack(a) is just an alias for a List(a)
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pub type Stack(a) =
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List(a)
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/// An empty stack is an empty list.
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pub const empty = []
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/// is_empty(s) checks if the stack s is empty.
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pub fn is_empty(stack: Stack(a)) -> Bool {
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case stack {
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[] -> True
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_ -> False
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}
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}
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/// push(s,x) pushes the element x onto the stack s.
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pub fn push(stack: Stack(a), x: a) -> Stack(a) {
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[x, ..stack]
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}
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/// peek(s) returns the TOS.
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pub fn peek(stack: Stack(a)) -> Result(a, Nil) {
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case stack {
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[] -> Error(Nil)
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[h, ..] -> Ok(h)
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}
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}
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/// pop(s) pops an element from the TOS, and returns that
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/// and the modified stack.
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pub fn pop(stack: Stack(a)) -> Result(#(a, Stack(a)), Nil) {
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case stack {
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[h, ..tl] -> Ok(#(h, tl))
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_ -> Error(Nil)
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}
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}
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