The Reverse Polish Notation evaluator using only call stack

Yuki Ito — Sun, 08 Jul 2018 15:44:10 +0000

I wrote evaluator for RPN(Reverse Polish Notation) using the call stack in Go.

package main

import (
    "bufio"
    "fmt"
    "os"
    "strconv"
)

func main() {
    r := bufio.NewReader(os.Stdin)

    var v []interface{}
    for {
        var s string
        if _, err := fmt.Fscan(r, &s); err != nil {
            break
        }

        var t interface{}
        n, err := strconv.Atoi(s)
        if err == nil {
            t = n
        } else {
            t = []rune(s)[0]
        }

        v = append(v, t)
    }

    calc(v)  // should be nil
}

type f func(int) f

func calc(v []interface{}) f {
    if len(v) == 0 {
        return f(func(n int) f {
            fmt.Println(n)
            return nil
        })
    }

    switch t := v[0].(type) {
    case int:
        return calc(v[1:])(t)
    case rune:
        return c(v[1:], t)
    default:
        panic(t)
    }
}

func c(v []interface{}, t rune) f {
    switch t {
    case '+':
        return op(v, func(a, b int) int {
            return a + b
        })
    case '-':
        return op(v, func(a, b int) int {
            return a - b
        })
    default:
        return op(v, func(a, b int) int {
            return a * b
        })
    }
}

func op(v []interface{}, fn func(int, int) int) f {
    return f(func(b int) f {
        return f(func(a int) f {
            return calc(v)(fn(a, b))
        })
    })
}

It inputs the space-separated notation like 1 2 + 3 4 + + and prints like 10.

I guess it do same things as the usual way to solve RPN(using real stack, not call stack) but unsure. Does it make sense?

pkg-config matters tripped me up in compiling porg

Yuki Ito — Tue, 05 Dec 2017 01:47:41 +0000

In compiling porg, I struggled with pkg-config failings so I'll left memo.

It was really smooth and no problem in past, but now it's failing on my refreshed PC as Ubuntu 17.10.

$ tar xf porg-0.10.tar.gz
$ ./configure

[...]

configure: error: Package requirements (gtkmm-3.0 >= 3.4.0) were not met:

No package 'gtkmm-3.0' found

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables GTKMM_CFLAGS
and GTKMM_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.

OK, let's install gtkmm-3.0.

$ sudo apt install libgtkmm-3.0-dev
$ ./configure

...

No package 'gtkmm-3.0' found

...

No changes on error message.

$ pkg-config gtkmm-3.0 --libs --cflags
Package gtkmm-3.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gtkmm-3.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gtkmm-3.0' found

Hmm... For some reason, gtkmm-3.0.pc is not recognized from pkg-config.

Where is PKG_CONFIG_PATH?

$ echo $PKG_CONFIG_PATH

$

Oh, it's not set.

Ubuntu Manpage: pkg-config - Return metainformation about installed libraries

As the above manual, even if the environment variable is not set, pkg-config sees /usr/lib/pkgconfig, /usr/local/lib/pkgconfig, /usr/share/pkgconfig, /usr/local/share/pkgconfig.

OK. So, the where is gtkmm-3.0?

$ dpkg -L libgtkmm-3.0 | grep '\.pc'
/usr/lib/x86_64-linux-gnu/pkgconfig/gdkmm-3.0.pc
/usr/lib/x86_64-linux-gnu/pkgconfig/gtkmm-3.0.pc

Out of referenced paths. What is /usr/lib/x86_64-linux-gnu?

It seems to be called "MultiArch tuple".

Multiarch/Tuples - Debian Wiki

It shows ABI and CPU instruction types.

My architecture is x86_64-linux for sure so just adding it to $PKG_CONFIG_PATH.

$ export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/usr/lib/x86_64-linux-gnu
$ pkg-config gtkmm-3.0 --libs --cflags
Package xproto was not found in the pkg-config search path.
Perhaps you should add the directory containing `xproto.pc'
to the PKG_CONFIG_PATH environment variable
Package 'xproto', required by 'xau', not found

Hmm. Now xproto is needed.

Ubuntu – File list of package x11proto-core-dev/trusty-updates/all

It seems to be already installed and at /usr/share/pkgconfig so let's add it also to $PKG_CONFIG_PATH.

$ export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/usr/share/pkgconfig
$ pkg-config gtkmm-3.0 --libs --cflags
-pthread -I/usr/include/gtkmm-3.0 -I/usr/lib/x86_64-linux-gnu/gtkmm-3.0/include -I/usr/include/atkmm-1.6 -I/usr/include/gtk-3.0/unix-print -I/usr/inc
lude/gdkmm-3.0 -I/usr/lib/x86_64-linux-gnu/gdkmm-3.0/include -I/usr/include/giomm-2.4 -I/usr/lib/x86_64-linux-gnu/giomm-2.4/include -I/usr/include/pa
...

Looks good.

And ./configure; make; make install succeeded also.

DEV Community: Yuki Ito

The Reverse Polish Notation evaluator using only call stack

pkg-config matters tripped me up in compiling porg