CompileMath

Command: CompileMath


Description

CompileMath converts a string containing a mathematical expression
in traditional infix notation to a procedure using the
standard postfix notation of SLI. The algorithm is:
1. replace traditonal operators like "-" and "+" with
SLI literals like /sub and /add
2. decompose the string into tokens using the standard
SLI scanner
3. compile the sequence of tokens to a SLI postfix expression
using the predictive recursive-descent parser described in
chapter 2 of the Dragon Book.
The result is the unevaluated expression. This enables the user
to store the expression for later reevaluation.
Parameters

string is the mathematical expression
proc is the unevaluated expression in SLI postfix notation
Author
Diesmann
Bugs

The present version fails for doubles with negative exponents
because the lexer just replaces all "-" with /sub. A slightly
smarter lexer using a regular expression can solve this problem.
Synopsis
string CompileMath -> proc
References

[1] The Dragon Book 1988 chapter 2
Examples

( 5 + 3 * 7 ) CompileMath exec --> 26
( 5 * (3 + 7) ) CompileMath exec --> 50
( 5 + x * 7 ) CompileMath --> {5 x 7 mul add}
( 3 + exp 5 ) CompileMath --> {3 5 exp add}
( 3 + exp ( x ) ) CompileMath --> {3 x exp add}
( 3 + exp ( -x ) ) CompileMath --> {3 x neg exp add}
( 3 * exp (sin 2)) CompileMath --> {3 2 sin exp mul}
( 3 * exp sin 2 ) CompileMath --> {3 2 sin exp mul}
(4 * - 7) CompileMath exec --> -28
(2^3) CompileMath --> {2 3 pow}
(5+3*2^3) CompileMath --> {5 3 2 3 pow mul add}
(5+3*2^3-4) CompileMath --> {5 3 2 3 pow mul add 4 sub}
(5+3*2^3/4) CompileMath --> {5 3 2 3 pow mul 4 div add}
(5+3*2^-3) CompileMath --> {5 3 2 3 neg pow mul add}
(4) CompileMath --> {4}
() CompileMath --> {}
(a=7+3) CompileMath --> {/a 7 3 add dup rolld Set}
(a=7+3;) CompileMath --> {/a 7 3 add dup rolld Set pop}
(a=7+3;6) CompileMath --> {/a 7 3 add dup rolld Set pop 6}
(a=7+4;b=2*exp(-2.0/10)) CompileMath --> {/a 7 4 add dup rolld Set pop /b 2 2.0 neg 10 div exp mul dup rolld Set}
(Function({x+2} 'x)) CompileMath --> {{x 2 add} /x Function}
(f=Function({x+2} 'x)) CompileMath --> {/f {x 2 add} /x Function dup rolld Set}
(f={#+2}) CompileMath --> {/f {<< >> begin /# Set # 2 add end} dup rolld Set}
(f={#1-#2}) CompileMath --> {/f {<< >> begin /#2 Set /#1 Set #1 #2 sub end} dup rolld Set}
({#1-#2}) CompileMath exec --> {<< >> begin /#2 Set /#1 Set #1 #2 sub end}
([4 3 2]) CompileMath --> {[4 3 2]}
(x=7+[4 3 2]*2) CompileMath --> {/x 7 [ 4 3 2 ] 2 mul add dup rolld Set}
([]) CompileMath --> {[]}
(<< 'x : [-3 9]*2 'y : 7 >>) CompileMath --> {<< /x [ 3 neg 9 ] 2 mul /y 7 >>}
(<< >>) CompileMath --> {<< >>}
(5+3 // Function( {2*x+1} 'x) ) CompileMath exec --> 17
(1+(5+3 // Function( {2*x+1} 'x)) ) CompileMath exec --> 18
( [ 3 [ 2 1] -9] // Flatten) CompileMath exec --> [3 2 1 -9]
( [ 3 [ 2 1] -9] // Flatten // {Select(# {#<3})} ) CompileMath exec --> [2 1 -9]
(5+3 // {#+1} ) CompileMath exec --> 9
(7 5 // {#1-#2}) CompileMath exec --> 2

File
lib/sli/mathematica.sli
Remarks

The function can be improved by using a more powerful parsing
scheme. The predictive recursive parsing scheme is used here
as an educational example.