VAL incomplete

[zarsoft]

In ZX SPECTRUM:

LET x = 2
PRINT VAL "2*x"

Prints 4

But on the compiler gives 0

How about adding variables from "a" to "z" in VAL?

[boriel]

This cannot be done in compiled BASIC. VAL "2*x" will need the ROM VAL, which calls the BASIC interpreter. This will need to store the variables in Sinclair BASIC Format which takes more space and is slow so the ROM interpreter will find the variable "x" in the BASIC Variables region.
Currently, a compiled variable like that of the example takes 1 byte (just the space needed to store the number). For Sinclair BASIC it will always be a Float (5 bytes, and slow) + the variable name "x" encoded in another region, etc.
So VAL here will behave as most BASICs, convert a STRING to a number or return 0 if it cannot decode it (indeed Sinclair BASIC VAL is very powerful).
There is a library function to call the BASIC interpreter, BTW, but it won't work in this case because it still needs the "x" variable.

[zarsoft]

VAL "2*x" will need the ROM VAL.

Then, I will do it the hard way:

LET X = 5
LET F$ = "2*X"

LET G$ = VALx$( F$)
( G$ = "2*5" )

PRINT VAL G$
(result = 10)

Code:

' PROGRAM VALx
' (c) ZarSoft 2023 Pascalated Boriel ZX BASIC
' Written by Ze Oliveira

#include <input.bas>  ' number = VAL INPUT(12)
#include <screen.bas> ' SCREEN$ function
#include <attr.bas>   ' ATTR function

'--- Pascalated Boriel ---
#define PROGRAM   REM
#define BEGIN    REM
'#define CONST     CONST
#define VAR       DIM
#define INTEGER   LONG
#define REAL      FLOAT
#define CHAR      STRING
'#define STRING    STRING
#define BOOLEAN   UBYTE
#define TYPE      AS
'#define WHILE    WHILE
#define REPEAT    DO
#define UNTIL     LOOP UNTIL
#define PROCEDURE  SUB
CONST   TRUE      TYPE BOOLEAN = 1
CONST   FALSE     TYPE BOOLEAN = 0

PROGRAM VALx

VAR X TYPE REAL
VAR Y TYPE REAL

FUNCTION VARaz (V$ TYPE STRING) TYPE REAL
VAR R TYPE REAL
IF V$ = "Z"
  R = Z
ELSE IF V$ = "Y"
  R = Y
ELSE IF V$ = "X"
  R = X
ENDIF 
RETURN R
END FUNCTION

FUNCTION VALx$ (S$ TYPE STRING) TYPE STRING
VAR R$ TYPE STRING
R$ = ""
FOR i = 0 TO LEN S$ -1
  IF S$(i) >= "A"
    LET R$ = R$ + STR$ VARaz( S$(i) )
  ELSE
    LET R$ = R$ + S$(i)
  ENDIF 
NEXT i
RETURN R$
END FUNCTION

PROGRAM VALx
VAR x,y,z TYPE INTEGER
VAR F$ TYPE STRING
VAR G$ TYPE STRING
VAR sx,sy TYPE REAL
VAR sx0,sy0 TYPE REAL
VAR first TYPE BOOLEAN
LET F$ = "9/(1+8*X*X+8*Y*Y)"
FOR y = -3 TO 0
  LET first = TRUE
  FOR x = -5 TO 5
    LET X = x*0.5
    LET Y = y*0.5
    LET G$ = VALx(F$)
    PRINT AT 0,0;"F(x,y)=";G$,,
    LET z = VAL(G$)
    LET sx = 120 + 20*x - 2.5*y
    LET sy = 75 + 6*y + 2.5*x + 10.1*z
    IF first
      first = FALSE
      PLOT sx,sy
    ELSE
      DRAW sx-sx0,sy-sy0
    ENDIF
    LET sx0 = sx
    LET sy0 = sy 
  NEXT x
NEXT y
END PROGRAM

[zarsoft]

Then, I will do it the hard way:

I have updated
https://www.boriel.com/forum/showthread.php?tid=2428