Write a "Hello" interpreter

Question

Background

Hello is a language "written" by Anne Veling, which errors if the program does not contain only h, and will print Hello World for every h

Task

You are to write an interpreter/compiler for Hello.

Example in Python

import os
i = input("Program: ")
for a in i:
    if a != 'h':
        print("err")
        quit()
    else:
        print("Hello World")

Details

• If the program is not only hs, it must print err or error (case-insensitive)
• It's okay if you print "Hello World"s before your program discovers a non-h character and errors, however, the program must halt if a non-h
• You may throw an error, as long as you print err/error before throwing, or by using a custom error builtin, like raise SyntaxError('err') in python. (basically, you have to purposefully error with err/error
• Assume the program will not be empty
• Output can have a trailing newline, space, or nothing to separate Hello Worlds
• If a program has multiple lines, it should error (due to \n not being an h)
• You can assume that input will always be ASCII 33-126 and 10 (decimal)
• The hs are case sensitive (so H is not a valid program) instruction is found
• This is code-golf, shortest answer wins

Test cases

Input:

h

Output:

Hello World

Input:

hhhhhh

Output:

Hello WorldHello WorldHello WorldHello WorldHello WorldHello World

(again, it doesn't matter whether it's spaces, newlines, or nothing to separate `Hello World`s

Input:

rubbish

Output:

err

Input:

huh

Output:

Hello Worlderr

Or

err

First challenge so please have mercy

Answer 1

Lenguage, \$1.42 \times 10^{122}\$ bytes

minus a lot of bytes thanks to Kevin Cruijssen and Bubbler

hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh...

This is 142099843608359281286315447494338058415442968773543757980908246691462388164856076679905341690709953072132211450166077106439 hs, which also makes it a valid Hello program, though not one you'd want to run. The original brainfuck code is 140 135 bytes:

,[>-[<-->-----]+<--[>]>[[-->-[>>+>-----<<]<--<---]>-.>>>+.>>..+++.>>.>.<<<.+++.------.<<-.[>]>>>>,>]<]<[[>++<+++++]>-.+++++++++++++..>]

Try it online!

This prints Hello World every time it sees a h through a modification of the shortest known Hello, World! program, stopping the loop and printing err if it sees anything other than a h.

Answer 2

Python 3, 49 bytes

lambda s:{*s}-{'h'}and'err'or'Hello World'*len(s)

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Python 2, 51 bytes

lambda s:s.strip('h')and'err'or'Hello World'*len(s)

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Python 2, 51 bytes

lambda s:['err','Hello World'*len(s)]['h'+s==s+'h']

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Answer 3

APL (Dyalog Unicode), 32 bytes (SBCS)

Anonymous tacit prefix function.

{'h'=⍵:'Hello World'⋄-⎕←'err'}⍤0

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{…}⍤0 replace each character (⍵) with the result of applying the following lambda to it:

 'h'=⍵: if the character is h:

  'Hello World' return the required phrase

 ⋄ else:

  ⎕←'err' print err
  - negate it (causing an error and terminating)

Answer 4

R, 76 bytes

function(p,n=nchar(p))ifelse(p==strrep('h',n),strrep("Hello World",n),'err')

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Should be a comment on https://codegolf.stackexchange.com/a/210520/98085 - I didn't realise you could do functions like that! Slight change to be more robust when n = 0 and to use direct comparison rather than regex. -1 byte thanks to https://codegolf.stackexchange.com/users/90265/zippymagician.

Bonus version with side-effects (like redefining subtraction) thanks to https://codegolf.stackexchange.com/users/92901/dingus.

R, 71 bytes

{`-`=strrep;function(p,n=nchar(p))`if`(p=='h'-n,'Hello world'-n,'err')}

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Answer 5

Gema, 23 characters

h=Hello World
?=err@end

Sample run:

bash-5.0$ echo -n 'hohoho' | gema 'h=Hello World;?=err@end'
Hello Worlderr

Gema (old version with err on empty code), 32 characters

\A\Z=err
h=Hello World
?=err@end

Try it online! / Try all test cases online!

Answer 6

x86-16 machine code, IBM PC DOS, 41 40 bytes

Binary:

00000000: be82 00ba 1801 b409 ac3c 0d74 0a3c 6874  .........<.t.<ht
00000010: 02b2 24cd 2174 f1c3 4865 6c6c 6f20 576f  ..$.!t..Hello Wo
00000020: 726c 6424 6572 7224                      rld$err$

Listing:

BE 0082         MOV  SI, 82H            ; SI to DOS PSP 
BA 0118         MOV  DX, OFFSET HW      ; point to 'Hello World' string 
B4 09           MOV  AH, 9              ; DOS write string function 
            CHAR_LOOP: 
AC              LODSB                   ; AL = next input byte 
3C 0D           CMP  AL, 0DH            ; is a CR (end of input string)? 
74 0A           JZ   DONE               ; if so, end 
3C 68           CMP  AL, 'h'            ; is an 'h'? 
74 02           JZ   WRITE_STR          ; if so, write Hello(s)
B2 24           MOV  DL, LOW OFFSET ER  ; otherwise, point to 'err' string 
            WRITE_STR: 
CD 21           INT  21H                ; write string to stdout 
74 F1           JZ   CHAR_LOOP          ; if 'h', keep looping 
            DONE:
C3              RET                     ; return to DOS 
            HW  DB  'Hello World$'
            ER  DB  'err$'

Standalone PC DOS executable COM program. Input via command line. This version prints Hello Worlderr if an error is in the input code.

And for fun (and since I did it first), this version will only print err if an error is in the code.

x86-16 machine code, IBM PC DOS, 47 45 44 bytes

Binary:

00000000: bf80 00ba 1c01 8a0d 4951 abb8 6809 f3ae  ........IQ..h...
00000010: 5974 04b2 28b1 01cd 21e2 fcc3 4865 6c6c  Yt..(...!...Hell
00000020: 6f20 576f 726c 6424 6572 7224            o World$err$

Listing:

BF 0080         MOV  DI, 80H            ; DI to DOS PSP 
BA 011C         MOV  DX, OFFSET HW      ; point to 'Hello World' string 
8A 0D           MOV  CL, BYTE PTR[DI]   ; CL = input length 
49              DEC  CX                 ; remove leading space from length 
51              PUSH CX                 ; save length for later 
AB              STOSW                   ; DI to start of command line input
B8 0968         MOV  AX, 0968H          ; AL = 'h', AH = 9 
F3/ AE          REPZ SCASB              ; search input for 'h': ZF if Hello, NZ if error
59              POP  CX                 ; restore input length 
74 04           JZ   HELLO_LOOP         ; if no error, write Hello(s) 
B2 28           MOV  DL, LOW OFFSET ER  ; otherwise, point to 'err' string 
B1 01           MOV  CL, 1              ; only show 'err' once 
            WRITE_LOOP: 
CD 21           INT  21H                ; write string to stdout 
E2 FC           LOOP WRITE_LOOP         ; loop until done 
C3              RET                     ; return to DOS 
            HW  DB  'Hello World$'
            ER  DB  'err$'

Props:

• -1 byte for both thanks to @MatteoItalia for suggestion to change only the low byte on the error string pointer.

Answer 7

Excel, 63 bytes

=IF(SUBSTITUTE(A1,"h","")="",REPT("Hello World",LEN(A1)),"err")

---

SUBSTITUTE(A1,"h","")="" returns TRUE iff A1 contains nothing but h.

REPT("Hello World",LEN(A1)) repeats the string for however many characters are in A1.

=If(Substitute(~)="",REPT(~),"err") returns the repeated string if A1 contains only h and err if it contains anything else.

Answer 8

Jelly, 17 bytes

^{14 if we can print Err as a substring of the output (e.g. “½,⁾ẇṭ»€!fƑ?”h TIO).}

“½,⁾ẇṭ»€“¹ṫ»fƑ?”h

Try it online!

How?

“½,⁾ẇṭ»€“¹ṫ»fƑ?”h - Main Link: program
               ”h - set right argument to 'h'
              ?   - if...
             Ƒ    - ...condition: is (program) invariant under?:
            f     -     keep only ('h's)
       €          - ...then: for each (c in program):
“½,⁾ẇṭ»           -     "Hello World"
        “¹ṫ»      - ...else: "error"
                  - implicit, smashing print

Answer 9

Ruby -0p, ^42...35 33 bytes

The idea to use the -0p flags (instead of -n like I originally had) came from @DomHastings's Perl answer, saving 4 bytes.

$_=/[^h]/?:err:'Hello World'*~/$/

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Reads the program from STDIN. A regex is used to check whether the program contains any character other than h. If so, print err; otherwise, print Hello World as many times as the number of characters in the program (given by ~/$/).

Using a bare regex literal as a boolean is a deprecated Perlism that (since Ruby 1.9) only works with the -n or -p flags.

Answer 10

05AB1E, 17 bytes

'hÃQig”Ÿ™‚ï”×ë'‰ë

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Big thanks to @Kevin for your dictionary compression tool!

And once again, Kevin has struck and managed to shave 3 bytes from my answer! So the aforementioned thanks is to be multiplied by a massive magnitude.

Explained (old)

Ð'hÃQig”Ÿ™‚ï”и»ë"err
Ð                       # Triplicate the input. STACK = [input, input, input]
 'h                     # Push the letter 'h'. STACK = [input, input, input, 'h']
   Ã                    # Keep _only_ the letter h in the input. STACK = [input, input, input.keep('h')]
    Q                   # Compare this with the original input. STACK = [input, 1 OR 0]
     i                  # If the comparison is truthy (i.e. it's only h's):
      g                 #   Push the length of the input. STACK = [len(input)]
       ”Ÿ™‚ï”           #   Push the compressed string "Hello World". STACK = [len(input), "Hello World"]
             и»         #   Repeat that string length of input times and join upon newlines. STACK = ["\n".join("Hello World" * len(input))]
               ë        # Else:
                "err    #   Push the string "err" to the stack. STACK = [input, "err"]
                        # Implicitly output the top of the stack
   
         

Answer 11

Haskell (Hugs 2006), 31 bytes

mapM(\'h'->putStr"Hello World")

Pending a question to the OP r.e. "error" in a larger error message. The spec says "it must print err or error", which it does on Hugs 2006, specifically the Raskell 1.0.13 interpreter based on Hugs 2006:

> mapM(\'h'->putStr"Hello World") "huh"
Hello World
Program error: pattern match
failure: ww_v4136 'u'

Answer 12

Arn, 24 bytes

ùÝ└ån<⁼aLw$■v&Z(#▄╗└·I╔║

Try it!

Explained

Unpacked: (${="h"})#=#&&'yt bs'^#||"err

And this is why I need to add an if else...

      (              Begin expression
        $            Filter
          {          Block with index of _
              _      Implicit
            =        Equals
              "h"    String
          }          End block
          _          Variable initialized to STDIN; implied
      )              End expression
    #                Length
  =                  Equals
      _              Implied
    #
&&                   Boolean AND
    'yt bs'        Compressed string equal to "Hello World"
  ^                  Repeated
      _              Implied
    #
||                   Boolean OR
  "err

Answer 13

SNOBOL4 (CSNOBOL4), 94 bytes

	I =INPUT
	I NOTANY('h')	:S(E)
	OUTPUT =DUPL('Hello World',SIZE(I))	:(END)
E	OUTPUT ='err'
END

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	I =INPUT					;* Read input
	I NOTANY('h')	:S(E)				;* If there is a character that's not 'h' in the input, goto E
	OUTPUT =DUPL('Hello World',SIZE(I))	:(END)	;* else print "Hello World" repeatedly and goto END
E	OUTPUT ='err'					;* print 'err'
END

Answer 14

JavaScript, 49 bytes

-4 bytes if we can throw an error instead of outputting a string.

f=([c,...a])=>c?c==`h`?`Hello World`+f(a):`err`:a

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Answer 15

JavaScript 72 66 bytes

-6 bytes thanks to @Ismael Miguel

alert(/^h*$/.test(a=prompt())?a.replace(/h/g,'Hello World'):'err')

Answer 16

flex, ^{76 \$\cdots\$ 55} 52 bytes

%%
h puts("Hello World");
[^h] puts("err");exit(1);

Put the above code in a file called hello.l and make the interpreter with:

flex hello.l && gcc lex.yy.c -o hello -lfl

Trying it on my terminal:

> echo -n hhh|./hello.exe
Hello World
Hello World
Hello World

With newline:

> echo hhh|./hello.exe
Hello World
Hello World
Hello World
err

notice the err because of the trailing newline echo normally sends.

With non-h character:

> echo -n hhhehhh|./hello.exe
Hello World
Hello World
Hello World
err

Answer 17

C (gcc), 71 65 bytes

f(char*p){p=*p-'h'?*p&&puts("err"):f(p+1)||!puts("Hello World");}

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• Thanks to @rtpax for saving 6!

f(char*p){p= - function tacking a program and returning with the eax trick, reusing p.
Calls itself recursively.
Recursion happens before program execution so if all steps are correct a false value is returned and the program is executed.
If there's an error a truthy value is returned and program is not executed at all, an error message is displayed.

*p-'h'? `...` :f(p+1)||!puts("Hello World");
 - check each character in program : if h  continue recursion and
   if result is false program do its job.
p is true  if there was an error, false instead.

 - if not h stop recursion and :
*p            - if end of program 
p  is false
&&puts("err") - if not end of program display error
p  is true.

---

61 58 bytes alternative less interesting solution which runs the program and stops when an error happens

f(char*p){*p&&puts(*p-'h'?"err":"Hello World")>4&&f(p+1);}

• Saved 3 thanks to @rtpax !

Answer 18

Python 3, 52 bytes

lambda x:(x=='h'*len(x))*len(x)*'Hello World'or'err'

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Answer 19

Python 3, 58 bytes

lambda s:s and s=="h"*len(s)and"Hello World"*len(s)or"err"

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Answer 20

Japt, ²³ 19 bytes

-4 bytes thanks to @Shaggy

rh ?`r`:¡`HÁM Wld

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Explanation

rh ?`...`:¡`...
   ?              // if
rh                //   input with 'h' removed
    `...`         // then "err"
         :        // else
          ¡       //   each char in input
           `...   //   replaced with "Hello World"

Answer 21

Pip, 28 27 bytes

aRM'h?"err""Hello World"X#a

-1 byte from DLosc.

If the string without h's is empty, print "Hello World" required number of times.

Otherwise, error.

This program errors on empty input as well.

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Answer 22

Python 3, 57 52 bytes

lambda a:a=='h'*len(a)and'Hello World'*len(a)or'err'

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Answer 23

Vim, ⁴⁸ 47 bytes

Thanks to @DLosc for -1 bytes

:g/\_$\_^\|[^h]/norm HcGerr
:s/h/Hello World/g

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The :g command is a bit convoluted, but there's a reason for that. The [^h] part will match all non-h characters, but it won't match newlines. $ or \n will match end-of-line, which means they will match a single line without a newline. To make it match only when there are multiple lines, I used \_$\_^. This will only match newlines (\_$) that are followed by another line (\_^).

For some reason, this doesn't work properly in TIO, so programs where the only non-h characters are newlines won't error. However, this does work properly in Vim.

Explanation:

:g/    (x)     /     (y)     # If x exists, execute y:
   \_$\_^                    #  x -> An end-of-line followed by a start-of-line;
         \|[^h]              #   OR any character that isn't 'h'
                norm HcGerr  #  y -> Delete all lines, then print 'err'

:s/h/Hello World/g           # Replace every 'h' with 'Hello World'

Answer 24

MathGolf, 23 20 bytes

'h-╛æ╖•p0{δ╕○ô 'W╕7ÿ

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Explanation:

'h-                  '# Remove all "h" from the (implicit) input-string
   ╛                  # Pop, and if it's now truthy (thus non-empty):
    æ                 #  Use the following four characters as single code-block:
     ╖•p              #   Push compressed string "err"
        0             #   And push a 0
         {            # Either loop 0 times,
                      # or loop over each character of the (implicit) input-string:
          δ           #  Titlecase the implicitly pushed current character ("h"→"H")
           ╕○ô        #  Push compressed string "ello"
                      #  Push " "
               'W    '#  Push "W"
                 ╕7ÿ  #  Push compressed string "orld"
                      # (implicitly output the entire stack joined together as result)

Answer 25

SimpleTemplate 0.84, 92 63 bytes

This challenge was simple, yet fun!

Simply checks if the input is just "hhh...." and outputs the text, or outputs "err" to STDOUT:

{@ifargv.0 matches"@^h+$@"M}{@eachM.0}Hello World{@/}{@else}err

The big byte saving was due to the-cobalt's comment:

Outputting to STDOUT is fine, so you could use your 63 byte version.

---

Ungolfed:

Below is a more readable version of the code:

{@if argv.0 matches "@^h+$@"}
    {@each argv.0 as h}
        {@echo "Hello World"}
    {@/}
{@else}
    {@echo "err"}
{@/}

---

You can try this on: http://sandbox.onlinephpfunctions.com/code/e35a07dfbf6b3b56c2608aa86028b395ef457129

Answer 26

PowerShell, 44 bytes

$args|%{if($_-104){'err';exit}"Hello World"}

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Takes input by splatting

Answer 27

Befunge-93, 58 56 bytes

~:1+!#v_"h"-#v_"dlroW olleH",,,,,,,,,,,  
  @,,,@#"err"<

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How does it work?

~                         # Read a character.

:1+!                      # Check whether we read -1 (end of input);
                          # this leaves 1 on the stack if we are at 
                          # the end of the input, else 0.

#v_                       # Exit the program if we're at the end
 @                        # end of the input.

"h"-                      # Compare the read character with the
                          # character "h", if equal, we leave 0 on
                          # the stack, otherwise, non-zero.

          #v_             # If we read anything but "h", print "err"
@,,,@#"err"<              # and exit the program.

"dlroW olleH",,,,,,,,,,,  # Print "Hello World"

Answer 28

GFA Basic (Atari ST), 125 bytes

INPUT a$
FOR i=1 TO LEN(a$)
b$=MID$(a$,i,1)
IF b$="h"
PRINT "Hello World"
ELSE
PRINT "err"
EXIT IF 1
ENDIF
NEXT I

Answer 29

Io, 63 bytes

method(:,:foreach(X,if(X!=104,"err"print-,"Hello World"print)))

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Explanation

method(i,                         // Take input
    i foreach(X,                  // For every item:
        if(X!=104,                //     If the codepoint isn't 104:
             "err"print           //         print "err" (w/o nl)
                       -          //         Subtract "err" by the "Object" class (causes error)
             ,"Hello World"print  //     Otherwise, print "Hello World" (w/o nl)
)))

Answer 30

C (gcc), 84 80 bytes

-4 bytes thanks to ceilingcat. It's beautiful!

main(c,v)char**v;{*v[1]++-'h'?*--v[1]&&puts("err"):main(puts("Hello World"),v);}

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Not so fancy, but I like that it's a complete program :)

"Normal" version:

#include <stdio.h>

int main(int argc, char** argv)
{
    if (*argv[1]++ - 'h')
        return *--argv[1] && puts("err");
    else
        return main(puts("Hello World"), argv);
}