Difference between revisions of "Forth parser"
From ScienceZero
(→Example 1) |
(→Variable inference) |
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if there are more than 0 variables emit '''DIM #<largest index>''' as the first instruction of the function. | if there are more than 0 variables emit '''DIM #<largest index>''' as the first instruction of the function. | ||
+ | |||
+ | |||
+ | == How to encode numbers == | ||
+ | if number = 0 then | ||
+ | emit '''LDC #0''' | ||
+ | else | ||
+ | find the leftmost hex digit n that is not 0 | ||
+ | emit '''LDC #n''' | ||
+ | zero out that digit | ||
+ | for each remaining digit n, zero or not | ||
+ | emit '''LDE #n''' | ||
== Example 1 == | == Example 1 == |
Revision as of 17:14, 24 April 2018
Contents
Variable inference
Variables are stored locally on the return stack. Any word that starts with ">" is a write to a variable. For each word in function If word starts with ">" Add the word to an ordered list of unique words that starts with ">", remove the leading ">" If there are more than 16 variables emit error Emit STL #<index in the ordered list> If word is in the list but does not start with ">" Emit LDL #<index in the ordered list> if there are more than 0 variables emit DIM #<largest index> as the first instruction of the function.
How to encode numbers
if number = 0 then emit LDC #0 else find the leftmost hex digit n that is not 0 emit LDC #n zero out that digit for each remaining digit n, zero or not emit LDE #n
Example 1
: lsl for dup + next ; ( Simple complete function that implements left shift by repeated addition ) ":" this tells the parser to define a new function "lsl" is the name of the function Adr Value 0 0xF0 ( for ) 1 0xE0 ( dup ) 2 0xC0 ( add ) 3 0xF1 ( next ) ";" tells the parser that it has reached the end of the definition The parser should create an "object" in memory like: "lsl",0xF0,0xE0,0xC0,0xF1
Default opcode equivalency for forth words
Forth string - opcode + - add - - sub * - mul / - div
dup - dup