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Add warning about evaluation model.

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Danila Fedorin 2020-08-15 01:37:57 -07:00
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content/blog/haskell_lazy_evaluation/index.md
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@ -103,6 +103,17 @@ needed to compute the final answer can exist, unsimplified, in the tree.
Why don't we draw a few graphs to get familiar with the idea? Why don't we draw a few graphs to get familiar with the idea?
### Visualizing Graphs and Their Reduction ### Visualizing Graphs and Their Reduction
__A word of caution__: the steps presented below may significantly differ
from the actual graph reduction algorithms used by modern compilers.
In particular, this section draws a lot of ideas from Simon Peyton Jones' book,
[_Implementing functional languages: a tutorial_](https://www.microsoft.com/en-us/research/publication/implementing-functional-languages-a-tutorial/).
However, modern functional compilers (i.e. GHC) use a much more
complicated abstract machine for evaluating graph-based code,
based on -- from what I know -- the [spineless tagless G-machine](https://www.microsoft.com/en-us/research/wp-content/uploads/1992/04/spineless-tagless-gmachine.pdf).
In short, this section, in order to build intuition, walks through how a functional program
evaluated using graph reduction _may_ behave; the actual details
depend on the compiler.
Let's start with something that doesn't have anything fancy. We can Let's start with something that doesn't have anything fancy. We can
take a look at the graph of the expression: take a look at the graph of the expression: