From dcbb72306821e0856c32944a54ea93902ef2949f Mon Sep 17 00:00:00 2001 From: Marshall Lochbaum Date: Mon, 13 Jun 2022 13:07:24 -0400 Subject: Implement high-rank array notation [] (including destructuring) --- docs/implementation/vm.html | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) (limited to 'docs/implementation/vm.html') diff --git a/docs/implementation/vm.html b/docs/implementation/vm.html index ba5731db..ba96ac12 100644 --- a/docs/implementation/vm.html +++ b/docs/implementation/vm.html @@ -43,7 +43,7 @@

The starting index refers to the position in bytecode where execution starts in order to evaluate the block. Different bodies will always have the same set of special names, but the variables they define are unrelated, so of course they can have different counts. The given number of variables includes special names, but list of names and export mask don't.

The program's symbol list is included in the tokenization information t: it is 0⊑2⊑t. Since the entire program (the source code passed in one compiler call) uses this list, namespace field accesses can be performed with indices alone within a program. The symbol list is needed for cross-program access, for example if •BQN returns a namespace.

Instructions

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The following instructions are defined (those without names are tentatively reserved only). The ones emitted by the self-hosted BQN compiler are marked in the "used" column. Instructions marked "NS" are used only in programs with namespaces, and those marked "HE" are used only with headers : or predicates ?. Only those marked "X" are needed to support the compiler and self-hosted runtime.

+

The following instructions are defined (those without names are tentatively reserved only). The ones emitted by the self-hosted BQN compiler are marked in the "used" column. Only those marked "X" are needed to support the compiler and self-hosted runtime. "NS" indicates instructions used only in programs with namespaces, "HE" is for headers : or predicates ?, and "HR" is for high-rank array notation [].

@@ -130,8 +130,8 @@ - - + + @@ -410,6 +410,12 @@ + + + + + + @@ -526,9 +532,9 @@

When a block is pushed with DFND, an instance of the block is created, with its parent frame set to be the frame of the currently-executing block. Setting the parent frame when the block is first seen, instead of when it's evaluated, is what distinguishes lexical from dynamic scoping. If it's an immediate block, it's evaluated immediately, and otherwise it's pushed onto the stack. When the block is evaluated, its frame is initialized using any arguments passed to it, the next instruction's index is pushed onto the return stack, and execution moves to the first instruction in the block. When the RETN instruction is encountered, an index is popped from the return stack and execution returns to this location. As an alternative to maintaining an explicit return stack, a block can be implemented as a native function that creates a new execution stack and returns the value in it when the RETN instruction is reached. This approach uses the implementation language's call stack for the return stack.

Local variables are manipulated with the VARO (or VARU) and VARM instructions, which load the value of a variable and a reference to it (see the next section) respectively. These instructions reference variables by frame depth and slot index. The frame depth indicates in which frame the variable is found: the current frame has depth 0, its block's parent frame has depth 1, and so on. The slot index is an index within that frame.

Slots should be initialized with some indication they are not yet defined. The variable can be defined with SETN only if it hasn't been defined yet, and can be accessed with VARO or VARU or modified with SETU, SETM, or SETC only if it has been defined.

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Variable references: ARRM VARM SETN SETU SETM SETC

+

Variable references: ARRM ARRH VARM SETN SETU SETM SETC

A variable reference indicates a particular frame slot in a way that's independent of the execution context. For example, it could be a pointer to the slot, or a reference to the frame along with the index of the slot. VARM pushes a variable reference to the stack.

-

A reference list is a list of variable references or reference lists. It's created with the ARRM instruction. In the Javascript VM there's no difference between a reference list and an ordinary BQN list other than the contents.

+

A reference list is a list of variable references or reference lists. It's created with the ARRM instruction. In the Javascript VM there's no difference between a reference list and an ordinary BQN list other than the contents. The ARRH instruction converts this to a merged reference list, which matches an array of rank 1 or more by splitting it into cells.

The SETN, SETU, SETM, and SETC instructions set a value for a reference. If the reference is to a variable, they simply set its value. For a reference list, the value needs to be destructured. It must be a list of the same length, and each reference in the reference list is set to the corresponding element of the value list.

SETM and SETC additionally need to get the current value of a reference. For a variable reference this is its current value (with an error if it's not defined yet); for a reference list it's a list of the values of each reference in the list.

0EARRHHR Merge top of stack (for [])N total variables (m=n-1)
0BARRHl → aList to array
10 FN1C 𝕩 𝕤 → (𝕊 𝕩)
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