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Adds List.last #816

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merged 2 commits into from
Dec 22, 2020
Merged

Adds List.last #816

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51a3029
adds List.last
celsobonutti Dec 21, 2020
bbb7ee7
updates List.last LowLevel ops comments
celsobonutti Dec 21, 2020
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17 changes: 17 additions & 0 deletions cli/tests/repl_eval.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -282,6 +282,23 @@ mod repl_eval {
expect_success("List.sum [ 1.1, 2.2, 3.3 ]", "6.6 : F64");
}

// TODO add test cases for empty lists once error messages in the repl are correct
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Sure enough! I've filed a bug for this: #818

#[test]
fn list_first() {
expect_success(
"List.first [ 12, 9, 6, 3 ]",
"Ok 12 : Result (Num *) [ ListWasEmpty ]*",
);
}

#[test]
fn list_last() {
expect_success(
"List.last [ 12, 9, 6, 3 ]",
"Ok 3 : Result (Num *) [ ListWasEmpty ]*",
);
}

#[test]
fn empty_record() {
expect_success("{}", "{} : {}");
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9 changes: 9 additions & 0 deletions compiler/builtins/src/std.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -465,6 +465,15 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {

add_type(
Symbol::LIST_FIRST,
top_level_function(
vec![list_type(flex(TVAR1))],
Box::new(result_type(flex(TVAR1), list_was_empty.clone())),
),
);

// last : List elem -> Result elem [ ListWasEmpty ]*
add_type(
Symbol::LIST_LAST,
top_level_function(
vec![list_type(flex(TVAR1))],
Box::new(result_type(flex(TVAR1), list_was_empty)),
Expand Down
32 changes: 26 additions & 6 deletions compiler/builtins/src/unique.rs
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Expand Up @@ -451,14 +451,16 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
unique_function(vec![list_type(star1, a)], int_type(star2))
});

fn list_was_empty() -> SolvedType {
SolvedType::TagUnion(
vec![(TagName::Global("ListWasEmpty".into()), vec![])],
Box::new(SolvedType::Wildcard),
)
}

// List.first :
// Attr (* | u) (List (Attr u a)),
// -> Attr * (Result (Attr u a) (Attr * [ OutOfBounds ]*))
let list_was_empty = SolvedType::TagUnion(
vec![(TagName::Global("ListWasEmpty".into()), vec![])],
Box::new(SolvedType::Wildcard),
);

add_type(Symbol::LIST_FIRST, {
let_tvars! { a, u, star1, star2, star3 };

Expand All @@ -470,7 +472,25 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
SolvedType::Apply(Symbol::LIST_LIST, vec![attr_type(u, a)]),
],
)],
result_type(star2, attr_type(u, a), lift(star3, list_was_empty)),
result_type(star2, attr_type(u, a), lift(star3, list_was_empty())),
)
});

// List.last :
// Attr (* | u) (List (Attr u a)),
// -> Attr * (Result (Attr u a) (Attr * [ OutOfBounds ]*))
add_type(Symbol::LIST_LAST, {
let_tvars! { a, u, star1, star2, star3 };

unique_function(
vec![SolvedType::Apply(
Symbol::ATTR_ATTR,
vec![
container(star1, vec![u]),
SolvedType::Apply(Symbol::LIST_LIST, vec![attr_type(u, a)]),
],
)],
result_type(star2, attr_type(u, a), lift(star3, list_was_empty())),
)
});

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101 changes: 101 additions & 0 deletions compiler/can/src/builtins.rs
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Expand Up @@ -64,6 +64,7 @@ pub fn builtin_defs_map(symbol: Symbol, var_store: &mut VarStore) -> Option<Def>
LIST_SET => list_set,
LIST_APPEND => list_append,
LIST_FIRST => list_first,
LIST_LAST => list_last,
LIST_IS_EMPTY => list_is_empty,
LIST_SINGLE => list_single,
LIST_REPEAT => list_repeat,
Expand Down Expand Up @@ -152,6 +153,7 @@ pub fn builtin_defs(var_store: &mut VarStore) -> MutMap<Symbol, Def> {
Symbol::LIST_SET => list_set,
Symbol::LIST_APPEND => list_append,
Symbol::LIST_FIRST => list_first,
Symbol::LIST_LAST => list_last,
Symbol::LIST_IS_EMPTY => list_is_empty,
Symbol::LIST_SINGLE => list_single,
Symbol::LIST_REPEAT => list_repeat,
Expand Down Expand Up @@ -1897,6 +1899,105 @@ fn list_first(symbol: Symbol, var_store: &mut VarStore) -> Def {
)
}

/// List.last : List elem -> Result elem [ ListWasEmpty ]*
///
/// List.last :
/// Attr (* | u) (List (Attr u a)),
/// -> Attr * (Result (Attr u a) (Attr * [ OutOfBounds ]*))
fn list_last(symbol: Symbol, var_store: &mut VarStore) -> Def {
let arg_var = var_store.fresh();
let bool_var = var_store.fresh();
let list_var = var_store.fresh();
let len_var = var_store.fresh();
let num_var = var_store.fresh();
let list_elem_var = var_store.fresh();
let ret_var = var_store.fresh();

// Perform a bounds check. If it passes, delegate to List.getUnsafe.
let body = If {
cond_var: bool_var,
branch_var: var_store.fresh(),
branches: vec![(
// if-condition
no_region(
// List.len list != 0
RunLowLevel {
op: LowLevel::NotEq,
args: vec![
(len_var, Int(num_var, 0)),
(
len_var,
RunLowLevel {
op: LowLevel::ListLen,
args: vec![(list_var, Var(Symbol::ARG_1))],
ret_var: len_var,
},
),
],
ret_var: bool_var,
},
),
// list was not empty
no_region(
// Ok (List.getUnsafe list (Num.sub (List.len list) 1))
tag(
"Ok",
vec![
// List.getUnsafe list (Num.sub (List.len list) 1)
RunLowLevel {
op: LowLevel::ListGetUnsafe,
args: vec![
(list_var, Var(Symbol::ARG_1)),
(
len_var,
// Num.sub (List.len list) 1
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that's cool

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This is the right approach for now, but actually we should use subWrap from #664 (once that's been implemented), because Num.sub should do overflow checking, and there's no chance of overflow yet.

(I say "should do" because currently only Num.add actually does it...maybe that's a good next project, actually!)

RunLowLevel {
op: LowLevel::NumSub,
args: vec![
(
arg_var,
// List.len list
RunLowLevel {
op: LowLevel::ListLen,
args: vec![(list_var, Var(Symbol::ARG_1))],
ret_var: len_var,
},
),
(arg_var, Int(num_var, 1)),
],
ret_var: len_var,
},
),
],
ret_var: list_elem_var,
},
],
var_store,
),
),
)],
final_else: Box::new(
// list was empty
no_region(
// Err ListWasEmpty
tag(
"Err",
vec![tag("ListWasEmpty", Vec::new(), var_store)],
var_store,
),
),
),
};

defn(
symbol,
vec![(list_var, Symbol::ARG_1)],
var_store,
body,
ret_var,
)
}

#[inline(always)]
fn no_region<T>(value: T) -> Located<T> {
Located {
Expand Down
46 changes: 46 additions & 0 deletions compiler/gen/tests/gen_list.rs
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Expand Up @@ -1003,6 +1003,52 @@ mod gen_list {
);
}

#[test]
fn last_int_list() {
assert_evals_to!(
indoc!(
r#"
when List.last [ 12, 9, 6, 3 ] is
Ok val -> val
Err _ -> -1
"#
),
3,
i64
);
}

#[test]
#[ignore]
fn last_wildcard_empty_list() {
assert_evals_to!(
indoc!(
r#"
when List.last [] is
Ok _ -> 5
Err _ -> -1
"#
),
-1,
i64
);
}

#[test]
fn last_empty_list() {
assert_evals_to!(
indoc!(
r#"
when List.last [] is
Ok val -> val
Err _ -> -1
"#
),
-1,
i64
);
}

#[test]
fn get_empty_list() {
assert_evals_to!(
Expand Down
1 change: 1 addition & 0 deletions compiler/module/src/symbol.rs
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Expand Up @@ -841,6 +841,7 @@ define_builtins! {
17 LIST_CONTAINS: "contains"
18 LIST_SUM: "sum"
19 LIST_WALK: "walk"
20 LIST_LAST: "last"
}
5 RESULT: "Result" => {
0 RESULT_RESULT: "Result" imported // the Result.Result type alias
Expand Down