96 lines
2.2 KiB
Common Lisp
96 lines
2.2 KiB
Common Lisp
#!/usr/bin/env -S conlang-run
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//! A simple five-function pn calculator
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// TODO: enum constructors in the interpreter
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struct Atom(f64);
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struct Op(char, [Expr]);
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enum Expr {
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Atom(f64),
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Op(char, [Expr]),
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}
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// Evaluates an expression
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fn eval(expr: Expr) -> isize {
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match expr {
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Atom(value) => value,
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Op('*', [lhs, rhs]) => eval(lhs) * eval(rhs),
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Op('/', [lhs, rhs]) => eval(lhs) / eval(rhs),
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Op('%', [lhs, rhs]) => eval(lhs) % eval(rhs),
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Op('+', [lhs, rhs]) => eval(lhs) + eval(rhs),
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Op('-', [lhs, rhs]) => eval(lhs) - eval(rhs),
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Op('-', [lhs]) => - eval(lhs),
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Op(other, ..rest) => {
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panic("ERROR: Unknown operator: " + other)
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},
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other => {
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println(other);
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panic("ERROR: Unknown operation ^")
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}
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}
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}
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/// Parses expressions
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fn parse(line: [char], power: i32) -> (Expr, [char]) {
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fn map((expr, line): (Expr, [char]), f: fn(Expr) -> Expr) -> (Expr, [char]) {
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(f(expr), line)
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}
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line = space(line);
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let (lhs, line) = match line {
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['0'..='9', ..] => number(line),
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[op, ..rest] => {
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parse(rest, pre_bp(op)).map(|lhs| Op(op, [lhs]))
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},
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_ => panic("Unexpected end of input"),
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};
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while let [op, ..rest] = space(line) {
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let (before, after) = inf_bp(op);
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if before < power {
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break;
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};
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(lhs, line) = parse(rest, after).map(|rhs| Op(op, [lhs, rhs]));
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};
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(lhs, line)
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}
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fn number(line: [char]) -> (Expr, [char]) {
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let value = 0.0;
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while (let [first, ..rest] = line) && (let '0'..='9' = first) {
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value = value * 10.0 + (first as f64 - '0' as f64);
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line = rest;
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};
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(Atom(value), line)
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}
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fn space(line: [char]) -> [char] {
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match line {
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[' ', ..rest] => space(rest),
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line => line
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}
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}
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fn inf_bp(op: char) -> (i32, i32) {
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(|x| (2 * x, 2 * x + 1))(
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match op {
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'*' => 2,
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'/' => 2,
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'%' => 2,
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'+' => 1,
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'-' => 1,
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_ => -1,
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})
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}
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fn pre_bp(op: char) -> i32 {
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(|x| 2 * x + 1)(
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match op {
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'-' => 9,
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_ => -1,
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})
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}
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