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Thread: Introduction to Eval module

  1. #1
    thinBasic author ErosOlmi's Avatar
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    Introduction to Eval module

    Eval module is one of my preferred modules. This module allows dynamic math functions being evaluated from text strings opening the road of many different options.
    To start with this module here it is just little script using console for output:

    [code=thinbasic]
    USES "CONSOLE" '---We need Console module to write output
    USES "EVAL" '---We need Eval module to evaluate math strings

    DIM t0, t1 AS DOUBLE = TIMER '---Some timing variable
    DIM MyFunction AS STRING '---Will contain math function to eval

    '---Define Y = f(X) ... function
    MyFunction = "y = COS(x) * 10 + SIN(x)"

    '---Tells eval engine to define new 2 variables: x and y
    Eval_SetNumber("x", 0)
    Eval_SetNumber("y", 0)

    '---Define a looper and its max
    DIM Count AS LONG
    DIM MaxCount AS LONG VALUE 50

    FOR Count = -MaxCount to MaxCount
    '---Set X value
    Eval_SetNumber("x", Count)
    '---Eval MyFunction
    Eval(MyFunction)
    '---Write some info output
    CONSOLE_WRITELINE(format$(Count, "0000") & " " & Eval_GetNumber("y"))
    NEXT

    '---Measure the ending time
    t1 = TIMER

    '---Final results
    CONSOLE_WRITELINE("------------------------------------------------------")
    CONSOLE_WRITELINE("Time in seconds for " & str$(MaxCount * 2) & " loops: ")
    CONSOLE_WRITELINE(FORMAT$(t1-t0, "#0.00000"))
    CONSOLE_WRITELINE("------------------------------------------------------")

    '---Wait for a key to stop execution
    CONSOLE_WAITKEY
    [/code]

    More examples will come showing how to link script variable to Eval internal variables.
    Also check about execution speed ...
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  2. #2
    thinBasic MVPs kryton9's Avatar
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    Re: Introduction to Eval module

    That eval module is like petr's tbgl module, full of magic that makes wonderful things happen. My time was 0.047 seconds.
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