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Bool patterns #342

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merged 4 commits into from
Apr 21, 2022
Merged

Bool patterns #342

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e057e5f
Small documentation fixes
wezm Apr 8, 2022
2a22b78
Add support for boolean patterns
wezm Apr 20, 2022
1342e56
Rework SplitConstBranches a bit
wezm Apr 21, 2022
75c2531
Check for duplicate patterns
wezm Apr 21, 2022
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8 changes: 5 additions & 3 deletions fathom/src/core.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -55,7 +55,7 @@ pub enum Term<'arena> {
/// The entry information will let us know what rigidly bound parameters to
/// apply to the flexible variable during [evaluation]. The applied
/// parameters will correspond to the [function introductions] that will be
/// addded to the flexible solution during unification.
/// added to the flexible solution during unification.
///
/// We clone the entry information and perform the function eliminations
/// during evaluation because elaborating to a series of [function
Expand Down Expand Up @@ -143,10 +143,12 @@ pub enum Term<'arena> {
/// Constants.
Const(Const),
/// Constant eliminations.
///
/// (head_expr, branches, default_expr)
ConstElim(
&'arena Term<'arena>,
&'arena [(Const, Term<'arena>)],
&'arena Term<'arena>,
Option<&'arena Term<'arena>>,
),
}

Expand Down Expand Up @@ -402,7 +404,7 @@ def_prims! {
}

/// Constants
#[derive(Debug, Copy, Clone, PartialEq)]
#[derive(Debug, Copy, Clone, PartialEq, PartialOrd)]
pub enum Const {
Bool(bool),
U8(u8),
Expand Down
66 changes: 48 additions & 18 deletions fathom/src/core/semantics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -158,15 +158,15 @@ impl<'arena> Telescope<'arena> {
pub struct Split<'arena> {
rigid_exprs: SharedEnv<ArcValue<'arena>>,
branches: &'arena [(Const, Term<'arena>)],
default_expr: &'arena Term<'arena>,
default_expr: Option<&'arena Term<'arena>>,
}

impl<'arena> Split<'arena> {
/// Construct a case split.
pub fn new(
rigid_exprs: SharedEnv<ArcValue<'arena>>,
branches: &'arena [(Const, Term<'arena>)],
default_expr: &'arena Term<'arena>,
default_expr: Option<&'arena Term<'arena>>,
) -> Split<'arena> {
Split {
rigid_exprs,
Expand All @@ -181,6 +181,15 @@ impl<'arena> Split<'arena> {
}
}

pub type Branch<'arena> = (Const, ArcValue<'arena>);

#[derive(Clone, Debug)]
pub enum SplitConstBranches<'arena> {
Branch(Branch<'arena>, Split<'arena>),
Default(Closure<'arena>),
None,
}

/// Errors encountered while interpreting terms.
// TODO: include stack trace(??)
#[derive(Clone, Debug)]
Expand All @@ -190,6 +199,7 @@ pub enum Error {
InvalidFunctionElim,
InvalidRecordElim,
InvalidFormatRepr,
MissingConstDefault,
}

impl Error {
Expand All @@ -200,6 +210,7 @@ impl Error {
Error::InvalidFunctionElim => "invalid function elim",
Error::InvalidRecordElim => "invalid record elim",
Error::InvalidFormatRepr => "invalid format repr",
Error::MissingConstDefault => "missing default expression",
}
}
}
Expand Down Expand Up @@ -323,7 +334,7 @@ impl<'arena, 'env> EvalContext<'arena, 'env> {
let head_expr = self.eval(head_expr);
self.elim_context().apply_const(
head_expr,
Split::new(self.rigid_exprs.clone(), branches, &default_expr),
Split::new(self.rigid_exprs.clone(), branches, *default_expr),
)
}
}
Expand Down Expand Up @@ -563,18 +574,21 @@ impl<'arena, 'env> ElimContext<'arena, 'env> {
pub fn split_const_branches(
&self,
mut const_branches: Split<'arena>,
) -> Result<((Const, ArcValue<'arena>), Split<'arena>), Closure<'arena>> {
) -> SplitConstBranches<'arena> {
match const_branches.branches.split_first() {
Some(((r#const, output_expr), branches)) => {
const_branches.branches = branches;
let mut context =
EvalContext::new(&mut const_branches.rigid_exprs, self.flexible_exprs);
Ok(((*r#const, context.eval(output_expr)), const_branches))
SplitConstBranches::Branch((*r#const, context.eval(output_expr)), const_branches)
}
None => Err(Closure::new(
const_branches.rigid_exprs,
const_branches.default_expr,
)),
None => match const_branches.default_expr {
Some(default_expr) => SplitConstBranches::Default(Closure::new(
const_branches.rigid_exprs,
default_expr,
)),
None => SplitConstBranches::None,
},
}
}

Expand Down Expand Up @@ -650,7 +664,12 @@ impl<'arena, 'env> ElimContext<'arena, 'env> {
// Otherwise call default with `head_expr`
let mut rigid_exprs = split.rigid_exprs.clone();
rigid_exprs.push(head_expr);
EvalContext::new(&mut rigid_exprs, self.flexible_exprs).eval(split.default_expr)
match split.default_expr {
Some(default_expr) => {
EvalContext::new(&mut rigid_exprs, self.flexible_exprs).eval(default_expr)
}
None => panic_any(Error::MissingConstDefault),
}
}
// The computation is stuck, preventing further reduction
Value::Stuck(_, spine) => {
Expand Down Expand Up @@ -716,7 +735,7 @@ impl<'arena, 'env> ElimContext<'arena, 'env> {
(Prim::FormatDeref, [Elim::Fun(elem), Elim::Fun(_)]) => self.apply_repr(elem),
(Prim::FormatStreamPos, []) => Arc::new(Value::prim(Prim::PosType, [])),
(Prim::ReportedError, []) => Arc::new(Value::prim(Prim::ReportedError, [])),
_ => panic_any(Error::InvalidFormatRepr),
_ => Arc::new(Value::prim(Prim::FormatRepr, [format.clone()])),
}
}
Value::Stuck(_, _) => Arc::new(Value::prim(Prim::FormatRepr, [format.clone()])),
Expand Down Expand Up @@ -787,18 +806,21 @@ impl<'in_arena, 'out_arena, 'env> QuoteContext<'in_arena, 'out_arena, 'env> {

let default_expr = loop {
match self.elim_context().split_const_branches(split) {
Ok(((r#const, output_expr), next_split)) => {
SplitConstBranches::Branch((r#const, output_expr), next_split) => {
branches.push((r#const, self.quote(&output_expr)));
split = next_split;
}
Err(default_expr) => break self.quote_closure(&default_expr),
SplitConstBranches::Default(default_expr) => {
break Some(self.quote_closure(&default_expr))
}
SplitConstBranches::None => break None,
}
};

Term::ConstElim(
self.scope.to_scope(head_expr),
branches.into(),
self.scope.to_scope(default_expr),
default_expr.map(|expr| self.scope.to_scope(expr) as &_),
)
}
})
Expand Down Expand Up @@ -1063,16 +1085,24 @@ impl<'arena, 'env> ConversionContext<'arena, 'env> {
self.elim_context().split_const_branches(split1),
) {
(
Ok(((const0, output_expr0), next_split0)),
Ok(((const1, output_expr1), next_split1)),
SplitConstBranches::Branch((const0, output_expr0), next_split0),
SplitConstBranches::Branch((const1, output_expr1), next_split1),
) if const0 == const1 && self.is_equal(&output_expr0, &output_expr1) => {
split0 = next_split0;
split1 = next_split1;
}
(Err(default_expr0), Err(default_expr1)) => {
(
SplitConstBranches::Default(default_expr0),
SplitConstBranches::Default(default_expr1),
) => {
return self.is_equal_closures(&default_expr0, &default_expr1);
}
(_, _) => return false,
(SplitConstBranches::None, SplitConstBranches::None) => {
return true;
}
(_, _) => {
return false;
}
}
}
}
Expand Down
8 changes: 5 additions & 3 deletions fathom/src/env.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,12 +7,12 @@
//! combination of [de Bruijn indices][LocalVar] in terms and [de Bruijn
//! levels][GlobalVar] in values in order to avoid the expensive and error-prone
//! shifting operations that are often associated with nameless approaches to
//! environments. For mor information on this approach, see section 3.1 of
//! environments. For more information on this approach, see section 3.1 of
//! [Abel's habilitation thesis](https://www.cse.chalmers.se/~abela/habil.pdf).
//!
//! # Environments
//!
//! A number of different environment representations are used - where possible
//! A number of different environment representations are used. Where possible
//! we try to stick to flat, low-indirection environments like [`UniqueEnv`]
//! and [`SliceEnv`], but when we need to copy environments often, we use a
//! [`SharedEnv`] to increase the amount of sharing at the expense of locality.
Expand All @@ -24,7 +24,9 @@ type RawVar = u16;

/// A [de Bruijn index], which represents a variable counting the number of
/// binders between a variable occurrence and the binder that introduced the
/// variable. For example:
/// variable.
///
/// For example:
///
/// | Representation | Example (S combinator) |
/// | ----------------- | ----------------------- |
Expand Down
112 changes: 75 additions & 37 deletions fathom/src/surface/distillation.rs
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Expand Up @@ -74,14 +74,22 @@ impl<'interner, 'arena, 'env> Context<'interner, 'arena, 'env> {
Term::NumberLiteral((), number)
}

fn check_boolean_pattern(&mut self, boolean: bool) -> Pattern<()> {
let name = match boolean {
true => self.interner.borrow_mut().get_or_intern("true"),
false => self.interner.borrow_mut().get_or_intern("false"),
};
Pattern::Name((), name)
}

fn check_number_pattern<T: std::fmt::Display>(&mut self, number: T) -> Pattern<()> {
let number = self.interner.borrow_mut().get_or_intern(number.to_string());
Pattern::NumberLiteral((), number)
}

fn check_constant_pattern(&mut self, r#const: &core::Const) -> Pattern<()> {
match r#const {
core::Const::Bool(_boolean) => unimplemented!("boolean patterns"),
core::Const::Bool(boolean) => self.check_boolean_pattern(*boolean),
core::Const::U8(number) => self.check_number_pattern(number),
core::Const::U16(number) => self.check_number_pattern(number),
core::Const::U32(number) => self.check_number_pattern(number),
Expand Down Expand Up @@ -185,28 +193,43 @@ impl<'interner, 'arena, 'env> Context<'interner, 'arena, 'env> {
},
core::Term::ConstElim(head_expr, branches, default_expr) => {
let head_expr = self.synth(head_expr);
let default_branch = {
let name = self.push_rigid(None);
let default_expr = self.check(default_expr);
self.pop_rigid();

(Pattern::Name((), name), default_expr)
};

Term::Match(
(),
self.scope.to_scope(head_expr),
self.scope.to_scope_from_iter(
branches
.iter()
.map(|(r#const, output_expr)| {
match default_expr {
Some(default_expr) => {
let default_branch = {
let name = self.push_rigid(None);
let default_expr = self.check(default_expr);
self.pop_rigid();

(Pattern::Name((), name), default_expr)
};

Term::Match(
(),
self.scope.to_scope(head_expr),
self.scope.to_scope_from_iter(
branches
.iter()
.map(|(r#const, output_expr)| {
let pattern = self.check_constant_pattern(r#const);
let output_expr = self.check(output_expr);
(pattern, output_expr)
})
.chain(std::iter::once(default_branch)),
),
)
}
None => Term::Match(
(),
self.scope.to_scope(head_expr),
self.scope.to_scope_from_iter(branches.iter().map(
|(r#const, output_expr)| {
let pattern = self.check_constant_pattern(r#const);
let output_expr = self.check(output_expr);
(pattern, output_expr)
})
.chain(std::iter::once(default_branch)),
},
)),
),
)
}
}

_ => self.synth(core_term),
Expand Down Expand Up @@ -372,28 +395,43 @@ impl<'interner, 'arena, 'env> Context<'interner, 'arena, 'env> {
},
core::Term::ConstElim(head_expr, branches, default_expr) => {
let head_expr = self.synth(head_expr);
let default_branch = {
let name = self.push_rigid(None);
let default_expr = self.synth(default_expr);
self.pop_rigid();

(Pattern::Name((), name), default_expr)
};

Term::Match(
(),
self.scope.to_scope(head_expr),
self.scope.to_scope_from_iter(
branches
.iter()
.map(|(r#const, output_expr)| {
match default_expr {
Some(default_expr) => {
let default_branch = {
let name = self.push_rigid(None);
let default_expr = self.synth(default_expr);
self.pop_rigid();

(Pattern::Name((), name), default_expr)
};

Term::Match(
(),
self.scope.to_scope(head_expr),
self.scope.to_scope_from_iter(
branches
.iter()
.map(|(r#const, output_expr)| {
let pattern = self.check_constant_pattern(r#const);
let output_expr = self.synth(output_expr);
(pattern, output_expr)
})
.chain(std::iter::once(default_branch)),
),
)
}
None => Term::Match(
(),
self.scope.to_scope(head_expr),
self.scope.to_scope_from_iter(branches.iter().map(
|(r#const, output_expr)| {
let pattern = self.check_constant_pattern(r#const);
let output_expr = self.synth(output_expr);
(pattern, output_expr)
})
.chain(std::iter::once(default_branch)),
},
)),
),
)
}
}
}
}
Expand Down
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