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Fix n vs n-1 mistake

This commit is contained in:
Danila Fedorin 2020-02-23 21:20:32 -08:00
parent 419ab937b6
commit df051fd643
1 changed files with 5 additions and 5 deletions
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10
content/blog/05_compiler_execution.md
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@ -334,10 +334,10 @@ code for the global function:
{{< gmachine "Unwind-Global" >}}
{{< gmachine_inner "Before">}}
\( \text{Unwind} : i \quad a, a_0, a_1, ..., a_n : s \quad d \quad h[\substack{a : \text{NGlobal} \; n \; c \\ a_k : \text{NApp} \; a_{k-1} \; a_k'}] \quad m \)
\( \text{Unwind} : i \quad a, a_0, a_1, ..., a_{n-1} : s \quad d \quad h[\substack{a : \text{NGlobal} \; n \; c \\ a_k : \text{NApp} \; a_{k-1} \; a_k'}] \quad m \)
{{< /gmachine_inner >}}
{{< gmachine_inner "After" >}}
\( c \quad a_0', a_1', ..., a_n', a_n : s \quad d \quad h[\substack{a : \text{NGlobal} \; n \; c \\ a_k : \text{NApp} \; a_{k-1} \; a_k'}] \quad m \)
\( c \quad a_0', a_1', ..., a_{n-1}', a_{n-1} : s \quad d \quad h[\substack{a : \text{NGlobal} \; n \; c \\ a_k : \text{NApp} \; a_{k-1} \; a_k'}] \quad m \)
{{< /gmachine_inner >}}
{{< gmachine_inner "Description" >}}
Call a global function.
@ -345,12 +345,12 @@ code for the global function:
{{< /gmachine >}}
In this rule, we used a general rule for \\(a\_k\\), in which \\(k\\) is any number
between 0 and \\(n\\). We also expect the `NGlobal` node to contain two parameters,
between 1 and \\(n-1\\). We also expect the `NGlobal` node to contain two parameters,
\\(n\\) and \\(c\\). \\(n\\) is the arity of the function (the number of arguments
it expects), and \\(c\\) are the instructions to construct the function's tree.
The attentive reader will have noticed a catch: we kept \\(a\_n\\) on the stack!
This once again goes back to replacing a node in-place. \\(a\_n\\) is the address of the "root" of the
The attentive reader will have noticed a catch: we kept \\(a\_{n-1}\\) on the stack!
This once again goes back to replacing a node in-place. \\(a\_{n-1}\\) is the address of the "root" of the
whole expression we're simplifying. Thus, to replace the value at this address, we need to keep
the address until we have something to replace it with.