EmilySillars
commented
2 years ago Hi Max, Thank you for your comment and apologies on the late reply --
Restating compiler pipeline here for context:
Scanner --> Parser --> Lowering --> Type Inference --> Optimization --> Code Generation --> C code
Lowering Stage: The ouput of the parser gives us a representation of our input sslang program as a tree. Nodes in the tree represents parts of the input program. The "lowering" pass implemented in LowerAst.hs transforms every AST node into an equivalient IR node. After performing lowering, we are still representing our input sslang program as a tree in the compiler. The difference is that after lowering, there are fewer kinds of nodes in our tree, and each node is augmented with space for a type, t.
// an AST Expr Node ----- LowerAst.hs ----> // an IR Expr Node
data Expr data Expr t
= Id Identifier = Var VarId t
| Lit Literal | Data DConId t
| Apply Expr Expr | Lit Literal t
| Lambda [Pat] Expr | App (Expr t) (Expr t) t
| OpRegion Expr OpRegion | Let [(Binder, Expr t)] (Expr t) t
| NoExpr | Lambda Binder (Expr t) t
| Let [Definition] Expr | Match (Expr t) [(Alt, Expr t)] t
| While Expr Expr | Prim Primitive [Expr t] t
| Loop Expr deriving (Eq, Show, Typeable, Data, Functor, Foldable, Traversable)
| Par [Expr]
| IfElse Expr Expr Expr
| After Expr Expr Expr
| Assign Expr Expr
| Constraint Expr TypAnn
| Wait [Expr]
| Seq Expr Expr
| Break
| Match Expr [(Pat, Expr)]
| CQuote String
| CCall Identifier [Expr]
| ListExpr [Expr]
deriving (Eq, Show)The function lowerExpr inside lowerAst.hs has the type signature
lowerExpr :: A.Expr -> Compiler.Pass (I.Expr I.Annotations)
which means it transforms something of type A.Expr to into a monadic I.Expr.
Compiler.Pass is the monad that wraps most all our compiler computations on/transformations
of our representation of a sslang prorgam.
Current Compiler Error: You are getting a non-exhaustive pattern match warning because the function lowerExpr does not have a case for matching on an A.Expr of instance ListExpr.
You need to add a case to LowerExpr that transforms a ListExpr instance of A.Expr into an App instance of I.Expr.
ListExpr [Expr] ---- needs to turn into ----> App (Expr t) (Expr t) t
How to do this???
Here is an exercise to get you started thinking about this. Write down your answers and comment them on this draft PR before our next meeting. Also comment any questions you have (or slack message me, whichever you prefer) if you get stuck!
Exercise:
type List
Cons Int
Nil
main cin cout =
let y = (Cons 1 (Cons 2 (Cons 3 Nil)))
let x = [1, 2, 3]
()1) What does y look like as an AST node? 2) What does x look like as an AST node?
3) What should y look like as an IR node? 4) What should x look like as an IR node?
I'm writing up a worked example + solution for a similar exercise, and will post that here as soon as I'm finished with it.
Hi @EmilySillars I am still getting this error:
stack exec sslc -- tests/lists_sample.ssl > out/lists_sample.c sslc: src/IR/LowerAst.hs:(119,1)-(164,63): Non-exhaustive patterns in function lowerExprwhen trying to run my sample test. As we discussed last week I have been reading through the IR to get an idea of how App, and DConId work. I think my next steps should be adding the code for the ListExpr so that it can be generated by the IR in the way we have been discussing on slack, but unsure where that code should even go since the error is in LowerAst.