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lang: add explicit type widening (As) #122

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merged 13 commits into from
Mar 23, 2025
Merged

lang: add explicit type widening (As) #122

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019c36f
spec: add the semantics/grammar for `As`
zerbina Mar 6, 2025
226501f
source2il: implement `As`
zerbina Mar 6, 2025
deed0e7
tests: add tests for `As`
zerbina Mar 6, 2025
2868ba3
tests: simplify existing union tests
zerbina Mar 6, 2025
b310b13
Merge branch 'main' into source-lang-as
zerbina Mar 20, 2025
cad0e96
tests: add missing test output specs
zerbina Mar 21, 2025
a660ef7
spec: adjust the dynamic `As` semantics
zerbina Mar 21, 2025
424535a
tests: add two more tests for `As`
zerbina Mar 21, 2025
7ef3398
source2il: make sure to always copy
zerbina Mar 21, 2025
5450caa
spectest: update the known-issue list
zerbina Mar 21, 2025
ac7fe30
Merge branch 'main' into source-lang-as
zerbina Mar 22, 2025
80a2c47
spec: handle `As` in `update`
zerbina Mar 22, 2025
9724ee6
spectest: update the known issues list
zerbina Mar 22, 2025
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9 changes: 9 additions & 0 deletions languages/source.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,7 @@ const lang* = language:
Call(+expr)
FieldAccess(expr, IntVal(z))
At(expr, expr)
As(expr, texpr)
And(expr, expr)
Or(expr, expr)
If(expr, expr, expr)
Expand Down Expand Up @@ -302,6 +303,13 @@ const lang* = language:
where SeqTy(typ_2), typ_1
conclusion C_1, At(e_1, e_2), mut(typ_2)

rule "S-as":
premise mtypes(C_1, e_1, typ_1)
premise ttypes(C_1, texpr_1, typ_2)
condition typ_2 != VoidTy()
condition typ_1 <:= typ_2
conclusion C_1, As(e_1, texpr_1), typ_2

rule "S-asgn":
premise types(C_1, e_1, mut(typ_1))
premise mtypes(C_1, e_2, typ_2)
Expand Down Expand Up @@ -689,6 +697,7 @@ const lang* = language:
axiom "E-exprs", Exprs(TupleCons(), +e_1), Exprs(...e_1)
axiom "E-if-true", If(True, e_1, e_2), e_1
axiom "E-if-false", If(False, e_1, e_2), e_2
axiom "E-as", As(e_1, texpr), e_1 # a no-op

axiom "E-while", While(e_1, e_2), If(e_1, Exprs(e_2, While(e_1, e_2)), TupleCons())

Expand Down
1 change: 1 addition & 0 deletions languages/specification.md
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Expand Up @@ -20,6 +20,7 @@ expr ::= <ident>
| (Call <expr>+)
| (FieldAccess <expr> <intVal>)
| (At <expr> <expr>)
| (As <expr> <texpr>)
| (And <expr> <expr>)
| (Or <expr> <expr>)
| (If <expr> <expr> <expr>?)
Expand Down
13 changes: 12 additions & 1 deletion passes/source2il.nim
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Expand Up @@ -697,7 +697,11 @@ proc fitExpr(c; e: sink Expr, target: SemType): Expr =
else:
# TODO: this needs a better error message
c.error("type mismatch")
result = Expr(stmts: e.stmts, typ: errorType())
# still return a proper expression so that analysis can carry on
if target.kind == tkVoid:
result = Expr(typ: target, stmts: e.stmts)
else:
result = Expr(typ: target, stmts: e.stmts, expr: e.expr)

proc fitExprStrict(c; e: sink Expr, typ: SemType): Expr =
## Makes sure expression `e` fits `typ` exactly, reporting an error and
Expand Down Expand Up @@ -1274,6 +1278,13 @@ proc exprToIL(c; t: InTree, n: NodeIndex, expr, stmts): ExprType =
newCall(at, @[c.inlineLvalue(arr, stmts), c.capture(idx, stmts)]))
else:
result = errorType() + arr.attribs
of SourceKind.As:
let
(a, b) = t.pair(n)
e = c.exprToIL(t, a)
typ = c.expectNot(c.evalType(t, b), tkVoid)
expr = inline(c.fitExpr(e, typ), stmts)
result = typ + {} # lvalue-ness and mutability are discarded
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I'm still learning to read the source, but it seems that lvalue-ness and mutability dropping isn't there, I'm guessing it can't be represented?

I guess the drop is required right now because if we're actually widening the bits then a new location would be required?

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I'm still learning to read the source, but it seems that lvalue-ness and mutability dropping isn't there, I'm guessing it can't be represented?

It's there, albeit not easy to spot. exprToIL (the enclosing procedure) returns an ExprType, which is a type + qualifiers (ExprFlags, currently a bunch of flags), where the qualifiers track both mutability and lvalue-ness.

If the qualifiers were to be kept, the result assignment would look like this:

result = typ + e.attribs # e.attribs are the source expression's qualifiers

I guess the drop is required right now because if we're actually widening the bits then a new location would be required?

Yep, that's the idea. If no widening takes place, then no new location is needed, so the lvalue-ness and mutability could be kept, but I decided against it because:

  • to the human reader, a large context window is potentially required to know what a specific As does (the same problem exists in NimSkull with lvalue conversions)
  • the lvalue-ness/mutability changing depending on the target type could become an issue once/if per-procedure type inference is introduced

This doesn't have to (nor should it have to) be the final decision, however. If it turns out that the current rules are problematic (for whatever reason), we should alter them.

of SourceKind.Asgn:
let (a, b) = t.pair(n)
var dst = c.exprToIL(t, a)
Expand Down
4 changes: 3 additions & 1 deletion passes/syntax_source.nim
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Expand Up @@ -20,6 +20,7 @@ type
TupleCons
Seq
FieldAccess, At
As
Exprs
Asgn
Return
Expand All @@ -34,7 +35,8 @@ type

const
ExprNodes* = {IntVal, FloatVal, Ident, And, Or, If, While, Call, TupleCons,
Seq, FieldAccess, At, Asgn, Return, Unreachable, Exprs, Decl}
Seq, FieldAccess, At, As, Asgn, Return, Unreachable, Exprs,
Decl}
DeclNodes* = {ProcDecl, TypeDecl}
AllNodes* = {low(NodeKind) .. high(NodeKind)}

Expand Down
4 changes: 4 additions & 0 deletions tests/expr/t02_as.test
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@@ -0,0 +1,4 @@
discard """
output: "1 : (IntTy)"
"""
(As 1 (IntTy))
4 changes: 4 additions & 0 deletions tests/expr/t02_as_no_void_error.test
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@@ -0,0 +1,4 @@
discard """
reject: true
"""
(As 1 (VoidTy))
4 changes: 4 additions & 0 deletions tests/expr/t02_as_type_mismatch_error.test
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@@ -0,0 +1,4 @@
discard """
reject: true
"""
(As 1 (UnitTy))
3 changes: 1 addition & 2 deletions tests/expr/t05_union_type_1.test
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@@ -1,5 +1,4 @@
discard """
output: "100 : (UnionTy (IntTy) (FloatTy))"
"""
(ProcDecl (Ident "a") (UnionTy (IntTy) (FloatTy)) (Params)
(Return (IntVal 100)))
(As 100 (UnionTy (IntTy) (FloatTy)))
3 changes: 1 addition & 2 deletions tests/expr/t05_union_type_2.test
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@@ -1,5 +1,4 @@
discard """
output: "1.5 : (UnionTy (IntTy) (FloatTy))"
"""
(ProcDecl (Ident "a") (UnionTy (IntTy) (FloatTy)) (Params)
(Return (FloatVal 1.5)))
(As 1.5 (UnionTy (IntTy) (FloatTy)))
3 changes: 1 addition & 2 deletions tests/expr/t05_union_type_of_single_type.test
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@@ -1,5 +1,4 @@
discard """
output: "100 : (UnionTy (IntTy))"
"""
(ProcDecl (Ident "a") (UnionTy (IntTy)) (Params)
(Return (IntVal 100)))
(As 100 (UnionTy (IntTy)))
3 changes: 1 addition & 2 deletions tests/expr/t06_union_duplicate_types.test
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@@ -1,5 +1,4 @@
discard """
reject: true
"""
(ProcDecl (Ident "a") (UnionTy (IntTy) (IntTy)) (Params)
(Return (IntVal 100)))
(As 100 (UnionTy (IntTy) (IntTy)))
13 changes: 3 additions & 10 deletions tests/expr/t08_if_expr_unify_type_1.test
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@@ -1,13 +1,6 @@
discard """
description: "Ensure types unify for an if-expression"
"""
(Module
(ProcDecl (Ident "p") (UnionTy (IntTy) (FloatTy)) (Params)
(Return (IntVal 100)))

(ProcDecl (Ident "test") (UnionTy (IntTy) (FloatTy)) (Params)
(Return
(If (Ident "true")
(FloatVal 0.5)
(Call (Ident "p")))))
)
(If (Ident "true")
(FloatVal 0.5)
(As (IntVal 100) (UnionTy (IntTy) (FloatTy)))))
13 changes: 3 additions & 10 deletions tests/expr/t08_if_expr_unify_type_2.test
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@@ -1,13 +1,6 @@
discard """
description: "Ensure types unify for an if-expression"
"""
(Module
(ProcDecl (Ident "p") (UnionTy (IntTy) (FloatTy)) (Params)
(Return (IntVal 100)))

(ProcDecl (Ident "test") (UnionTy (IntTy) (FloatTy)) (Params)
(Return
(If (Ident "false")
(Call (Ident "p"))
(FloatVal 0.5))))
)
(If (Ident "false")
(As (IntVal 100) (UnionTy (IntTy) (FloatTy)))
(FloatVal 0.5))))
14 changes: 5 additions & 9 deletions tests/expr/t09_asgn_compatible_type.test
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@@ -1,12 +1,8 @@
discard """
output: "1.5 : (UnionTy (IntTy) (FloatTy))"
"""
(Module
(ProcDecl (Ident "union") (UnionTy (IntTy) (FloatTy)) (Params)
(Return (IntVal 100)))

(ProcDecl (Ident "test") (UnionTy (IntTy) (FloatTy)) (Params)
(Exprs
(Decl (Ident "x") (Call (Ident "union")))
(Asgn (Ident "x") (FloatVal 1.5))
(Return (Ident "x")))))
(Exprs
(Decl (Ident "x")
(As (IntVal 100) (UnionTy (IntTy) (FloatTy))))
(Asgn (Ident "x") (FloatVal 1.5))
(Ident "x"))
17 changes: 7 additions & 10 deletions tests/expr/t17_seq_copy_3.test
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@@ -1,13 +1,10 @@
discard """
output: "(array 1 2 3) : (UnionTy (IntTy) (SeqTy (IntTy)))"
"""
(Module
(ProcDecl union (UnionTy (IntTy) (SeqTy (IntTy))) (Params)
(Return 1))
(ProcDecl main (UnionTy (IntTy) (SeqTy (IntTy))) (Params)
(Exprs
(Decl x (Seq (IntTy) 1 2 3))
(Decl y (Call union))
(Asgn y x)
(Asgn (At x 0) 4)
(Return y))))
(Exprs
(Decl x (Seq (IntTy) 1 2 3))
(Decl y
(As 1 (UnionTy (IntTy) (SeqTy (IntTy)))))
(Asgn y x)
(Asgn (At x 0) 4)
y)
14 changes: 6 additions & 8 deletions tests/expr/t17_seq_nested_copy_3.test
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Expand Up @@ -2,11 +2,9 @@ discard """
description: "Sequences part of unions are fully copied when the union is"
output: "(array 1 2 3) : (UnionTy (IntTy) (SeqTy (IntTy)))"
"""
(Module
(ProcDecl union (UnionTy (IntTy) (SeqTy (IntTy))) (Params)
(Return (Seq (IntTy) 1 2 3)))
(ProcDecl main (UnionTy (IntTy) (SeqTy (IntTy))) (Params)
(Exprs
(Decl x (Call union))
(Decl y x)
(Return y))))
(Exprs
(Decl x
(As (Seq (IntTy) 1 2 3)
(UnionTy (IntTy) (SeqTy (IntTy)))))
(Decl y x)
y)
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