45 lines
1.7 KiB
Markdown
45 lines
1.7 KiB
Markdown
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---
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title: Compiling a Functional Language Using C++, Part 7 - Runtime
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date: 2019-08-06T14:26:38-07:00
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draft: true
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tags: ["C and C++", "Functional Languages", "Compilers"]
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---
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Wikipedia has the following definition for a __runtime__:
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> A [runtime] primarily implements portions of an execution model.
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We know what our execution model is! We talked about it in Part 5 - it's the
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lazy graph reduction we've been talking about. Creating and manipulating
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graph nodes is slightly above hardware level, and all programs in our
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functional language will rely on such manipulation (it's how they run!). Furthermore,
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most G-machine instructions are also above hardware level (especially unwind!).
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Push and Slide and other instructions are pretty complex instructions.
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Most computers aren't stack machines. We'll have to implement
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our own stack, and whenever a graph-building function will want to modify
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the stack, it will have to call library routines for our stack implementation:
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```C
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void stack_push(struct stack_s* s, struct node_s* n);
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struct node_s* stack_slide(struct stack_s* s, size_t c);
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/* other stack operation */
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```
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Furthermore, we observe that Unwind does a lot of the heavy lifting in our
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G-machine definition. After we build the graph,
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Unwind is what picks it apart and performs function calls. Furthermore,
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Unwind pushes Unwind back on the stack: once you've hit it,
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you're continuing to Unwind until you reach a function call. This
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effectively means we can implement Unwind as a loop:
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```C
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while(1) {
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// Check for Unwind's first rule
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// Check for Unwind's second rule
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// ...
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}
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```
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In this implementation, Unwind is in charge. We won't need to insert
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the Unwind operations at the end of our generated functions.
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