Difference between revisions of "Forth parser"
From ScienceZero
(→Variable inference) |
(→Variable inference) |
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For each word that starts with ">" | For each word that starts with ">" | ||
− | Add the word to an ordered list of | + | Add the word to an ordered list of unique words that starts with ">", remove the leading ">" |
Emit '''STL #<index in the ordered list>''' | Emit '''STL #<index in the ordered list>''' | ||
For each word that is in the list but does not start with ">" | For each word that is in the list but does not start with ">" |
Revision as of 17:09, 24 April 2018
Variable inference
Variables are stored locally on the return stack. Any word that starts with ">" is a write to a variable. For each word that starts with ">" Add the word to an ordered list of unique words that starts with ">", remove the leading ">" Emit STL #<index in the ordered list> For each word that is in the list but does not start with ">" Emit LDL #<index in the ordered list> If there are more than 16 variables emit error if there are more than 0 variables emit DIM #<largest index> as the first instruction of the function.
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 input text --> look up tables --> output binary How to encode numbers: if number = 0 then emit LDC #0 else find the topmost hex digit that is not 0, call it x emit LDC #x zero out that digit for each remaining digit y, zero or not emit LDE #y
Default opcode equivalency for forth words
Forth string - opcode + - add - - sub * - mul / - div
dup - dup