35 lines
1.3 KiB
Rust
35 lines
1.3 KiB
Rust
//! Desugars `while {...} else` expressions
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//! into `loop if {...} else break` expressions
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use crate::{ast::*, ast_visitor::fold::Fold};
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use cl_structures::span::Span;
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/// Desugars while-else expressions
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/// into loop-if-else-break expressions
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pub struct WhileElseDesugar;
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impl Fold for WhileElseDesugar {
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fn fold_expr(&mut self, e: Expr) -> Expr {
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let Expr { extents, kind } = e;
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let kind = desugar_while(extents, kind);
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Expr { extents: self.fold_span(extents), kind: self.fold_expr_kind(kind) }
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}
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}
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/// Desugars while(-else) expressions into loop-if-else-break expressions
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fn desugar_while(extents: Span, kind: ExprKind) -> ExprKind {
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match kind {
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// work backwards: fail -> break -> if -> loop
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ExprKind::While(While { cond, pass, fail: Else { body } }) => {
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// Preserve the else-expression's extents, if present, or use the parent's extents
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let fail_span = body.as_ref().map(|body| body.extents).unwrap_or(extents);
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let break_expr = Expr { extents: fail_span, kind: ExprKind::Break(Break { body }) };
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let loop_body = If { cond, pass, fail: Else { body: Some(Box::new(break_expr)) } };
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let loop_body = Expr { extents, kind: ExprKind::If(loop_body) };
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ExprKind::Loop(Loop { body: Box::new(loop_body) })
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}
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_ => kind,
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}
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}
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