From c309ac4c14b605ae5ddf49b3072b19c9433e7928 Mon Sep 17 00:00:00 2001 From: Danila Fedorin Date: Thu, 14 Nov 2019 11:05:17 -0800 Subject: [PATCH] Rename page and add pop instruction to part 5 of compiler series --- content/blog/00_compiler_intro.md | 2 +- content/blog/05_compiler_execution.md | 24 +++++++++++++++++-- ...emantics.md => 06_compiler_compilation.md} | 0 3 files changed, 23 insertions(+), 3 deletions(-) rename content/blog/{06_compiler_semantics.md => 06_compiler_compilation.md} (100%) diff --git a/content/blog/00_compiler_intro.md b/content/blog/00_compiler_intro.md index d43a464..4e12dcf 100644 --- a/content/blog/00_compiler_intro.md +++ b/content/blog/00_compiler_intro.md @@ -137,6 +137,6 @@ Here are the posts that I've written so far for this series: * [Typechecking]({{< relref "03_compiler_typechecking.md" >}}) * [Small Improvements]({{< relref "04_compiler_improvements.md" >}}) * [Execution]({{< relref "05_compiler_execution.md" >}}) -* [Compilation]({{< relref "06_compiler_semantics.md" >}}) +* [Compilation]({{< relref "06_compiler_compilation.md" >}}) * [Runtime]({{< relref "07_compiler_runtime.md" >}}) * [LLVM]({{< relref "08_compiler_llvm.md" >}}) diff --git a/content/blog/05_compiler_execution.md b/content/blog/05_compiler_execution.md index f2ffc7c..73c21e6 100644 --- a/content/blog/05_compiler_execution.md +++ b/content/blog/05_compiler_execution.md @@ -558,7 +558,9 @@ rule to Unwind: {{< /gmachine_inner >}} {{< /gmachine >}} -Just one more! Sometimes, it's possible for a tree node to reference itself. +Just a couple more special-purpose instructions, and we're done! + +Sometimes, it's possible for a tree node to reference itself. For instance, Haskell defines the [fixpoint combinator](https://en.wikipedia.org/wiki/Fixed-point_combinator) as follows: @@ -586,9 +588,27 @@ We can allocate an indirection on the stack, and call Update on it when we've constructed a node. While we're constructing the tree, we can refer to the indirection when a self-reference is required. +Lastly, we also define a Pop instruction, which just removes +some number of nodes from the stack. We want this because +calling Update at the end of a function modifies a node further up the stack, +leaving anything on top of the stack after that node as scratch work. We get +rid of that scratch work simply by popping it. + +{{< gmachine "Pop" >}} + {{< gmachine_inner "Before">}} + \( \text{Pop} \; n : i \quad a_1, a_2, ..., a_n : s \quad d \quad h \quad m \) + {{< /gmachine_inner >}} + {{< gmachine_inner "After" >}} + \( i \quad s \quad d \quad h \quad m \) + {{< /gmachine_inner >}} + {{< gmachine_inner "Description" >}} + Pop \(n\) nodes from the stack. + {{< /gmachine_inner >}} +{{< /gmachine >}} + That's it for the instructions. Knowing them, however, doesn't tell us what to do with our `ast` structs. We'll need to define rules to translate trees into these instructions, and I've already alluded to this when we went over `double 326`. However, this has already gotten pretty long, -so we'll do it in the next post: [Part 6 - Compilation]({{< relref "06_compiler_semantics.md" >}}). +so we'll do it in the next post: [Part 6 - Compilation]({{< relref "06_compiler_compilation.md" >}}). diff --git a/content/blog/06_compiler_semantics.md b/content/blog/06_compiler_compilation.md similarity index 100% rename from content/blog/06_compiler_semantics.md rename to content/blog/06_compiler_compilation.md