One-level evaluation

Carl Love — Thu, 06 Mar 2014 07:14:43 Z

Local variables and parameters evaluate differently from global variables. Quoting from ?eval (seventh paragraph of Description):

The default evaluation rules in Maple are full evaluation for global variables, and one-level evaluation for local variables and parameters.

When your eq2 (in procedure f) is evaluated to one level, that leaves its x unevaluated. So, the cure is to use eval(eq2), which forces a full recursive evaluation.

restart;
f:= proc()
local
     x,y,
     eq1:= 5+3*x=0,
     eq2:= 2+7*x-3*y-5*x*y=0
;
     x:= solve(eq1,x):
     y:= solve(eval(eq2),y):
lprint('x'=x,'y'=y);
end proc:

f();
x = -5/3, y = 29/16

To address your second question, about ||: The || operator simply was not intended to concatenate arbitrary expressions. It was intended as a convenient way to create indexed symbols. What you are trying to achieve can be easily done with the formatted print statement, printf:

printf("x is %a", -5/3);

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Markiyan Hirnyk — Thu, 06 Mar 2014 07:41:30 Z

@Carl Love Better late than never.

MaplePrimes - answers and comments on Question, solve is misbehaving

One-level evaluation

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