Difference between revisions of "Forth parser"
From ScienceZero
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| + | == 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 all 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. | ||
| + | |||
| + | This will | ||
| + | |||
== Example 1 == | == Example 1 == | ||
| − | : lsl for dup + next ; ( Simple complete function that implements left shift by repeated addition ) | + | ''': lsl for dup + next ;''' ( Simple complete function that implements left shift by repeated addition ) |
":" this tells the parser to define a new function | ":" this tells the parser to define a new function | ||
| Line 23: | Line 38: | ||
How to encode numbers: | How to encode numbers: | ||
| − | if number = 0 then emit LDC #0 | + | if number = 0 then emit '''LDC #0''' |
else | else | ||
find the topmost hex digit that is not 0, call it x | find the topmost hex digit that is not 0, call it x | ||
| − | emit LDC #x | + | emit '''LDC #x''' |
zero out that digit | zero out that digit | ||
for each remaining digit y, zero or not | for each remaining digit y, zero or not | ||
| − | emit LDE #y | + | emit '''LDE #y''' |
== Default opcode equivalency for forth words == | == Default opcode equivalency for forth words == | ||
Revision as of 17:07, 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 all 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.
This will
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
