projects:english_as_a_second_language_for_forth_programmers
ENGLISH AS A SECOND LANGUAGE FOR FORTH PROGRAMMERS
There is a difference between spelling a word and saying a
word. In normal communication we do not ess-pee-ee-ell-ell
words. Likewise we do not normally pronounce punctuation.
(Period.) Sometimes it is necessary to spell for complete
understanding but comprehension is generally easier when
natural language is spoken.
A language may also have special signs & symbols which are
normally "said", e.g., "&" and "#" are normally pronounced
"and" & "number". Spelling often has very little relationship
to the pronunciation, e.g., "lb" is "pound" & "cwt" is
"hundredweight".
Forth is
"a language of natural English words and signs using
machine oriented syntax for command and control of
machines".
The so-called natural pronunciation of Forth words given
in the Forth-79 and Forth-83 standard documents are mostly
spellings. Experience has shown that Forth programs are easier
to teach and understand when natural English words are used for
the special signs.
An obvious example of this is "#". The standard documents
give "sharp" as its natural pronunciation. This is patently
wrong. The musical sharp sign is similar to it but different.
The semantics of all occurrences of "#" in standard Forth words
are connected with numbers. "#" should be said "number" and
spelled "number-sign".
The standard specification of "@" is "value at <address>".
It makes more sense to say "value" than "fetch" when we read
it. Likewise "!" reads better as "set", which is what the
function is called in other high-level languages. E.g., the
body of the definition of "DEFINITIONS"
CURRENT @ CONTEXT !
reads naturally as
current value context set
This says What it does, not How it does it. This agrees with
the Forth-83 standard document, which says that "descriptive"
names are to be preferred to "procedural" names (section 4).
Reflection leads to "add" as the meaning of "+!". A
fragment of code
0 #LINE ! 1 #PAGE +!
reads naturally as
zero number-line set one number-page add
The so-called natural pronunciation of the apostrophe "'"
is given as "tick" in the Forth-83 standard document,
ignoring descriptive and procedural names. A better word for
this is "address". This also works well in compounds: from the
Perry Line-Editor read
'START 'LINE 'CURSOR 'FIND
as
address-start address-line address-cursor address-find
"compile-time-address" is a better name for "[']". In
general say "compile-time-name" for "[name]".
The function of the dot or period "." in Forth is
"display". The Forth word spelled "dot-quote" is used to
display a message; the Forth word spelled "ABORT-quote" is used
to abort with a message. They should be said "display-message"
and "abort-message", which are perfect descriptions.
Forth has three common conventions for names within
parentheses.
"(name)" is the default value of a vectored word. E.g.,
(CR) (KEY)
"(name)" is used by "name". E.g.,
(.)
"(name)" is compiled by "name". E.g.,
(.") (ABORT") (LOOP)
Notice that the third case is a subset of the second.
All these uses can be covered by "primitive".
(CR) primitive CR
(KEY) primitive key
(.) primitive display
(.") primitive display message
(ABORT") primitive abort message
(LOOP) primitive loop
"," is used to lay down values in the dictionary, and we
say "lay" or "lay down" or "build" for this function.
Just as Forth is said to have been discovered, not
invented, so the foregoing words were discovered in the order
given. Having come so far, we would like to go the rest of the
way.
"[" is used to initiate interpretation, but "INTERPRET" is
a word in the controlled word-set. We pronounce it "evaluate".
A stumbling stone in learning Forth is the difference
between "]", "COMPILE", and "[COMPILE]".
If we think of "]" as "construct" we have a way to
distinquish "]" from the other two. "COMPILE" will "compile" a
defined word into the dictionary; "]" will do whatever is
necessary to "construct" the dictionary, including defined
words, literal values, logical structures, and anything else.
"[COMPILE]" is "compile-time compile", which accurately
describes what it does, compile the next word as a single word
at compile-time, not run-time.
Some examples to show how this hangs together.
: ASCII ( -- c ) BL WORD COUNT 1- ABORT" ?"
STATE @ IF [COMPILE] LITERAL THEN ; IMMEDIATE
"Define ASCII BL word count one-minus abort-message
question-mark state value if compile-time-compile literal
then. Immediate."
Note that punctuation was not pronounced. Punctuation
can be spelled when necessary for comprehension.
From the preceding paragraph we see how "(" should be
pronounced, i.e., "note". Likewise ".(" is "display-note".
From an integer-ascii conversion definition:
... [ ASCII A 10 - ] LITERAL ...
"... evaluate ascii A 10 minus construct literal ..."
The prefix "C" is used in Forth to show byte-related
operations. Just as "cwt" is pronounced "hundredweight" so
"C@", "C!", and "C," have the pronunciation "byte-value",
"byte-set", and "byte-lay(down)".
How about "possibly" or "maybe" for the question mark when
it is part of a word, e.g., "maybe DUP" for "?DUP" ?
We can say "define" for ":" as we did above. The ";" can
be silent punctuation, or we can use the Eastern "already" or
Western "y'know" until some-one has a better suggestion.
Here is a summary of the suggested pronunciations. Can
you think of any others?
# number
@ value
! set
+! add
' address
['] compile-time address
. display
." display message
ABORT" abort message
(name) primitive name
, lay down, or lay
[ evaluate
] construct
[COMPILE] compile-time compile
( note
.( display note
?... maybe ..., or possibly ...
: define
; already, or y'know.
FINIS
projects/english_as_a_second_language_for_forth_programmers.txt · Zuletzt geändert: 2013-06-06 21:27 von 127.0.0.1