On 11/25/12 11:08 PM, Richard O'Keefe wrote:
On 24/11/2012, at 5:26 PM, wren ng thornton wrote:
On 11/20/12 6:54 AM, [email protected] wrote:
Hello,
I know nothing about compilers and interpreters. I checked several
books, but none of them explained why we have to translate a
high-level language into a small (core) language. Is it impossible
(very hard) to directly translate high-level language into machine
code?
It is possible to remove stages in the standard compilation pipeline, and doing
so can speed up compilation time. For example, Perl doesn't build an abstract
syntax tree (for now-outdated performance reasons), and instead compiles the
source language directly into bytecode (which is then interpreted by the
runtime). This is one of the reasons why Perl is (or was?) so much faster than
other interpreted languages like Python etc.
I have found Perl anything from the same speed as AWK (reading and writing
lots of data with hardly any processing) to 10 times slower than AWK (with
respect to the 'mawk' implementation of AWK).
Perhaps I was too glib in saying "other interpreted languages"; I
certainly did not mean to include Sed and Awk (which I tend to consider
shell scripting more than interpreted programming). Also, I'm only
referring to the startup cost of parsing and compiling to bytecode[1],
not any other overhead of the actual languages themselves. There are
significant differences between the actual content of each language[2],
but that's a linguistic issue rather than an issue of how to design and
structure the compiler/interpreter.
[1] For one-liners and short programs, this startup cost tends to
dominate, which is why Perl does direct to bytecode. Perl was initially
intended to be a combination/replacement for Sed, Awk, Bash, etc; it
only turned into a full programming language later. That said, the
overhead for starting the Perl runtime is much higher than for Sed and
Awk, which is why many systems engineers still use Sed/Awk in their scripts.
[2] A notorious but too poorly known example is the implementation of
regexes where crufty old tools/languages like awk and grep vastly
outperform modern tools like Perl and Python:
http://swtch.com/~rsc/regexp/regexp1.html
To say nothing of the implementations of strings, hash tables, etc;
which you mentioned.
--
Live well,
~wren
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